Digital PDFs

EK-DMV11-TM-C01

September 1981

202 pages

Original

7.9MB

Document:	DMV11 Synchronous Controller Technical Manual
Order Number:	EK-DMV11-TM
Revision:	C01
Pages:	202
Original Filename:	http://bitsavers.org/pdf/dec/qbus/EK-DMV11-TM-001_DMV11_Synchronous_Controller_Technical_Manual_Sep81.pdf

OCR Text

EK-DMV11-TM-001

: DMV11
Synchronous Controller
Technical Manual
"
"

EK-DMV11-TM-001

DMV11
Synchronous Controller
Technical Manual

PREPARED BY EDUCATIONAL SERVICES
OF
DIGITAL EQUIPMENT CORPORATION

1st Edition, September 1981

Copyright © 1981 by Digital Equipment Corporation
The material in this manual is for informational purposes and is
subject to change without notice.
Digital Equipment Corporation assumes no responsibility for any
errors which may appear in this manual.

Printed in U.S.A.

This document was set on DIGITAL's DECset-8000 computerized
typesetting system.

The following are trademarks of Digital Equipment Corporation,
Maynard, Massachusetts:
DIGITAL
DEC
PDP
DECUS
UNIBUS

DECsystem-lO
DECSYSTEM-20
DIBOl
EDUSYSTEM
VAX
VMS

MASSBUS
OMNIBUS
OS/8
RSTS
RSX
lAS

CONTENTS

Page
PREFACE
CHAPTER 1

INTRODUCTION

1.1
1.2
1.3
1.4
1.5
1.6
1.6.1
1.6.2
1.7
1.7.1
1.7.2
1.7.3
1.8
1.8.1
1.8.2
1.8.3

INTRODUCTION.................................................................................................
INTRODUCTION TO MULTIPOINT................................................................
DMV11 GENERAL DESCRIPTION ..................................................................
STANDARD APPLICATIONS ...........................................................................
DMV11 SYSTEM OPERATION .........................................................................
COMMAND/RESPONSE STRUCTURES........................................................
Input Commands .............................................................................................
Output Responses ...........................................................................................
PROTOCOL SUPPORT........................................................................................
Data Messages .............................. ......... ...................................... ...................
Control Messages............................................................................................
Maintenance Messages...................................................................................
GENERAL SPECIFICATIONS ..........................................................................
Environmental Specifications .........................................................................
Electrical Specifications ............................................................................ ~....
Performance Specifications .......... ..................... ......................... ....................

CHAPTER 2

INSTALLATION

2.1
2.2
2.3
2.4
2.4.1
2.4.2
2.5
2.6
2.6.1
2.6.2
2.6.3
2.6.4

INTRODUCTION................................................................................................. 2-1
UNPACKING AND INSPECTION .................................................................... 2-1
INSTALLATION CONSIDERATIONS......................................... .................... 2-1
PREINSTALLATION CONSIDERATIONS..................................................... 2-2
Device Placement........................................ ................................................... 2-6
System Requirements..................................................................................... 2-6
INSTALLATION ....... ~.......................................................................................... 2-9
DMV11 SYSTEM TESTING ............................................................................... 2-10
Functional Diagnostic Testing ........................................................................ 2-10
DEC/XII System Exerciser .......................................................................... 2-10
Final Cable Connections.................. ....... ........................................................ 2-10
DMVl1 Link Testing ...................................................................................... 2-10

CHAPTER 3

COMMAND AND RESPONSE STRUCTURES

3.1
3.2
3.2.1
3.2.2
3.2.3
3.3
3.3.1
3.3.2

INTRODUCTION.................................................................................................
COMMAND STRUCTURE ............................................................. ....................
Control and Status Registers ....... ......... ........ ................. ....................... ..........
Input Commands Overview ............................................................................
Output Responses Overview ...........................................................................
DMVl1 INPUT COMMANDS ............................................................................
Microprocessor Control/Maintenance Command..........................................
Mode Definition Command............................................................................

iii

1-1
1-1
1-1
1-3
1-3
1-4
1-4
1-6
1-6
1-6
1-6
1-6
1-8
1-8
1-8
1-8

3-1
3-1
3-1
3-5
3-5
3-6
3-6
3-6

CONTENTS (Cont)

Page
3.3.3
3.3.4
3.4
3.4.1
3.4.2
3.4.3
3.5

Control Command ..................................................................._....................... 3-9
Buffer Address/Character Count (BAjCC) Command ................................ 3-16
DMVII OUTPUT RESPONSES .......................................................................... 3-18
Buffer Disposition Response ........................................................................... 3-19
Control Response ... ....................... ............... .... ........ ........ ..................... .......... 3-20
Information Response .... .................. ......... ........ .... ................ ..... ........... .......... 3-26
TSS/GSS ACCESS ............................................................................................... 3-26

CHAPTER 4

PROGRAMMING TECHNIQUES

4.1
4.2
4.2.1
4.2.2
4.2.3
4.3
4.3.1
4.3.2
4.3.2.1
4.3.2.2
4.3.3
4.4

INTRODUCTION................................................................................................. 4-1
COMMAND/RESPONSE DISCIPLINE AND HANDSHAKING ................. 4-1
Command Discipline ...................................................................................... 4-2
Retrieving Responses....... ....................................... ........ ......... ...... ......... ........ 4-3
CSR Interface Interactions ............................................................................ 4-3
DMVII START-UP ............................................................................................... 4-3
Configuration Procedure ................................................................................ 4-4
Specifying User-Defined Parameters ............................................................. 4-4
Specifying TSS Parameters ................................................................... 4-6
Specifying GSS Parameters.......... ............................................. ............ 4-11
Protocol Operation.......................................................................................... 4-13
CRITERIA FOR DETERMINING COMMUNICATIONS
LINK PARAMETERS.......................................................................................... 4-13
Setting the Selection Interval Timer .............................................................. 4-14
Setting the Babbling Tributary Timer ............................................................ 4-16
Setting the Streaming Tributary Timer .......................................................... 4-16
ERROR COUNTER ACCESS ............................................................................. 4-17
Reading the Counters..................................................................................... 4-17
Counter Skew .................................................................................................. 4-17
ERROR RECOVERY PROCEDURES ............................................................... 4-17
Recovery from Network Errors...................................................................... 4-18
Recovery from Threshold Errors............................................................ 4-18
Recovery from Babbling and Streaming Tributary Errors .................... 4-18
Recovery from Procedural Errors......... ............ .... ........... ..................... .......... 4-18
Recovery from a Nonexistent Memory Error ........................................ 4-18
Recovery from a Receive Buffer Too Small Error ................................. 4-19
Recovery from a Queue Overflow Error ................................................ 4-20
BOOTING A REMOTE STATION ..................................................................... 4-20
Steps Leading to a Remote Load Detect Boot. ............................................... 4-21
Steps Leading to a Power-On Boot ................................................................. 4-21
Steps Leading to an Invoke Primary MOP Boot ............................................ 4-22
DMVII Switch Settings for the Boot Functions ............................................ 4-22
Switch Settings for the Power-On Boot Function ................................... 4-22
Switch Settings for the Invoke Primary MOP Boot Function ................ 4-22
Switch Settings for the Remote Load Detect Boot Function ................. 4-23
MAINTENANCE REGISTER EMULATION ................................................... 4-23

4.4.1
4.4.2
4.4.3
4.5
4.5.1
4.5.2
4.6
4.6.1
4.6.1.1
4.6.1.2
4.6.2
4.6.2.1
4.6.2.2
4.6.2.3
4.7
4.7.1
4.7.2
4.7.3
4.7.4
4.7.4.1
4.7.4.2
4.7.4.3
4.8

CONTENTS (Cont)

Page
CHAPTERS

ASPECTS OF DMVll MICROCODE OPERATION

5.1
5.2
5.2.1
5.2.2
5.2.2.1
5.2.2.2
5.2.2.3
5.2.2.4
5.3
5.3.1
5.3.1.1
5.3.1.2
5.3.1.3
5.3.1.4
5.3.1.5
5.3.1.6
5.3.1.7
5.3.1.8
5.3.1.9
5.3.1.10
5.3.2
5.3.2.1
5.3.2.2
5.3.2.3
5.3.2.4
5.3.3
5.3.3.1
5.3.3.2
5.3.3.3
5.4
5.4.1
5.4.1.1
5.4.1.2
5.4.1.3
5.4.2
5.4.3
5.4.3.1
5.4.3.2

INTRODUCTION................................................................................................. 5-1
DMVII POLLING ALGORITHM ...................................................................... 5-1
Calculating Polling Urgency........................................................................... 5-2
Criteria for Determining Polling Parameters ................................................. 5-6
Determining a Value for DELTA T ....................................................... 5-6
Determining Values for Q and R............................................................ 5-7
Determining a Value for Poll Delay....................................................... 5-8
Determining a Value for DEAD T ......................................................... 5-8
ERROR COUNTERS ........................................................................................... 5-8
Data Link Error Counters............................................................................... 5-9
Data Errors Outbound............................................................................ 5-9
Data Errors Inbound .............................................................................. 5-11
Local Reply Timeouts ............................................................................ 5-11
Remote Reply Timeouts .......... .............. .................. ........... .................... 5-11
Local Buffer Errors.......................................... ................................. ..... 5-12
Remote Buffer Errors............................................................................. 5-12
Selection Timeouts .............. ....................................... ........ .................... 5-12
Data Messages Transmitted ....
5-12
Data Messages Received ............. :.......................................................... 5-12
Selection Intervals.................................................................................. 5-13
Station Error Counters ................ ............................................... .................... 5-13
Remote Station Errors ............................................................................ 5-13
Local Station Errors ............................................................................... 5-13
Global Header Block-Check Errors ....................................................... 5-14
Maintenance Data Field Block-Check Errors ........................................ 5-14
Threshold Error Counters............................................................................... 5-14
Transmit Threshold Errors.... ............ ........ ......................... ....... ............. 5-14
Receive Threshold Errors........ .............. ........ ........ ............. .................... 5-15
Selection Threshold Errors..................................................................... 5-15
DMVII MICROCODE INTERNAL DATA BASE OVERVIEW ..................... 5-15
Linked Lists ............ ................................ ........... ......................... ......... ..... ...... 5-15
The Free Linked List...................... ...... ............ .......... ........ .......... ..... ..... 5-16
The Response Linked List...................................................................... 5-18
Buffer Linked Lists ................................................................................ 5-18
Slot Mapping Table ........... ............... ..................... ............. ............. .......... ..... 5-19
TSS and GSS Structures................................................................................ 5-19
The Global Status Slot (GSS) ................................................................ 5-19
Tributary Status Slots (TSS) .................................................................. 5-19

CHAPTER 6

TECHNICAL DESCRIPTION

6.1
6.2
6.2.1

INTRODVCTION.................................................................................................
LOGIC DESCRIPTION .......................................................................................
Control and Address Decoder.........................................................................

I ..............................................................

6-1
6-1
6-1

CONTENTS (Cont)

Page
6.2.1.1
6.2.1.2
6.2.1.3
6.2.1.4
6.2.2
6.2.2.1
6.2.2.2
6.2.2.3
6.2.3
6.2.3.1
6.2.3.2
6.2.3.3
6.2.4
6.2.4.1
6.2.4.2
6.2.4.3
6.2.4.4
6.2.5
6.2.6
6.2.7
6.2.7.1
6.2.7.2

The 6502 Microprocessor ... ........... ... .... ... ................... ...... ............. ..... .... 6-1
Timing Circuits .............................................................................. :....... 6-2
6502 Data and Address Interface........................................................... 6-2
Address Decoders.. .......... ..... .... ........ ....... .... ..... .... ..... .......... ........ ....... .... 6-3
I/O Data Bus ......................................... ......................................................... 6-3
USYRT .................................................................................................. 6-3
USYRT Control..................................................................................... 6-3
Line Interface Control............................................................................ 6-6
DMVl1 Memory ............................................................................................. 6-6
ROM Control Storage ............................................................................ 6-6
RAM ...................................................................................................... 6-6
NPR In/Out Registers........................................................................... 6-6
LSI-II Bus Interface ...................................................................................... 6-7
LSI-II Bus DAL Interface .................................................................... 6-7
CSR Controller....................................................................................... 6-8
Interrupt Controller ........................... ;.................................................... 6-8
NPR Controller ...................................................................................... 6-9
Memory and Reset Control............................................................................ 6-9
Modem Interface ............................................................................................ 6-9
Integral Modem.............................................................................................. 6-10
Receive ................................................................................................... 6-10
Transmit ................................................................................................. 6-10

CHAPTER 7

SERVICE

7.1
7.2
7.3
7.3.1
7.3.2
7.3.2.1
7.3.2.2
7.3.2.3
7.3.3
7.4
7.4.l
7.4.2
7.5
7.6
7.6.l
7.6.2
7.6.3
7.6.4
7.6.5
7.6.6
7.6.6.1

SCOPE.................................................................................................................... 7-1
MAINTENANCE PHILOSOPHy....................................................................... 7-1
TROUBLESHOOTING TECHNIQUES FOR MULTIPOINT ......................... 7-1
Approach ........................................................................................................ 7-1
Error Counters................................................................................................ 7-7
Data Link Error Counters ...................................................................... 7-7
Station Error Counters ........................................................................... 7-11
Threshold Error Counters ....................................................................... 7-12
Error Counter Analysis ................................................................................... 7-13
MAINTENANCE ............................................................................................. :.... 7-16
Maintenance Mode......................................................................................... 7-16
Standard Operating Mode ........... ·................................................................... 7-16
PREVENTIVE MAINTENANCE (PM) ............................................................. 7-17
CORRECTIVE MAINTENANCE ;..................................................................... 7-17
DMV11 Static Logic Tests Parts 1 and 2 ....................................................... 7-17
DMV11 Static Logic Tests Parts 3,4, and 5 .................................................. 7-19
DMV11 Functional Diagnostic ....................................................................... 7-21
DMV11 Microdiagnostic Error Reporting ..................................................... 7-21
Data Communications Link Test Program (DCLT) ...................................... 7-21
DEC/XII DMV11 Modules .......................................................................... 7-25
DMD* .................................................................................................... 7-25

CONTENTS (Cont)

Page
7.6.6.2
7.6.7

DME* ..................................................................................................... 7-26
Soft Error Reports Under DEC/XlI ............................................................. 7-27

APPENDIX A

DDCMP IN A NUTSHELL

A.l
A.l.l
A.1.2
A.1.3
A.l.4
A.l.S
A.2
A.3

DDCMP ..................................................................................................................
Controlling Data Transfers........................... .......... .......................... ..............
Error Checking and Recovery............. .............................. ...................... .......
Character Coding ...........................................................................................
Data Transparency .........................................................................................
Data Channel Utilization ...................................................... ~.........................
PROTOCOL DESCRIPTION ........................................................ ......................
MESSAGE FORMAT ...........................................................................................

APPENDIXB

FLOATING DEVICE AND VECTOR ADDRESSES

B.l
B.2
B.3

FLOATING DEVICE ADDRESSES................................................................... B-1
FLOATING VECTOR ADDRESSES .................................................................. B-1
EXAMPLES OF DEVICE AND VECTOR ADDRESS ASSIGNMENT ......... B-5

APPENDIXC

MODEM CONTROL REGISTER FORMATS

C.l
C.2

MODEM CONTROL REGISTER FORMATS .................................................. C-l
RS-449 VERSUS RS-232-C.................................................................................... C-4

APPENDIXD

MODEM CONTROL

D.l
D.l.l
D.1.2

MODEM CONTROL .......... :................................................................................. D-l
Hardware Modem Control......... ............... ................................................. ..... D-l
Modem Control Implemented by the DMVII Microcode ............................. D-l

A-I
A-I
A-I
A-2
A-2
A-2
A-2
A-4

FIGURES
Figure No.
1-1
1-2
1-3
2-1
2-2
2-3
2-4

Title
DMVlls Used in Point-to-Point Applications ........................................................
DMVlls Used in Multipoint Applications .............................................................
General Summary of DMVII Command/Response Structure..............................
Local Network Topology.........................................................................................
Remote Network Topology .....................................................................................
M8053 Switch Locations ........................................................................................
M8064 Switch Locations ........................................................................................

Vll

Page
1-4
1-5
1-7
2-3
2-4
2-7
2-8

FIGURES (Cont)
Figure No.

2-5
2-6
2-7
2-8
2-9
2-10
2-11
2-12
2-13
2-14
3-1
3-2
3-3
3-4
3-5
3-6
3-7
3-8
3-9
3-10
4-1
4-2
4-3
5-1
5-2
5-3
5-4
5-5
5-6
5-7
5-8
5-9
5-10
5-11
6-1
6-2
6-3
6-4
6-5
6-6
6-7
6-8
7-1
7-2
_ 7-3

Title

Page

DMVII Switch Selectable Features ....................................................................... 2-13
Test Connector Insertion for the MS053 ................................................................. 2-16
Test Connector Insertion for the MS064 ................................................................. 2-17
DMVII Test Connectors ........................................................................................ 2-18
DMVII Cable Drawings ......................................................................................... 2-22
DMVl1 Remote System Cabling Diagram ............................................................ 2-25
DMVll to DMVl1 Integral (Local) Modem Cabling Diagram (Point-to-Point) .. 2-26
Half-Duplex Multipoint Network (Control Station End Node) ............................. 2-27
Full-Duplex Multipoint Network (Control Station End Node) .............................. 2-28
Full-Duplex Multipoint Network (Control Station Inner Node) ............................ 2-29
DMVII CSRs Byte and Word Symbolic Addresses ......-............................... ......... 3-2
Fixed and Variable Formats for Commands and Responses................................... 3-2
Microprocessor Control/Maintenance Command Format ..................................... 3-6
Initialization of the DMVII ................................................................................... 3-7
Mode Definition Command Format........................................................................ 3-S
Control Command Format ............................... ....................................................... 3-9
Buffer Address/Character Count Command Format. ............................................ 3-17
Buffer Disposition Response Format ...................................................................... 3-19
Control-Out Command Format IS-Bit Mode .......................................................... 3-26
Information Response Format ................................................................................ 3-27
CSR Interface Control Bits ............................. ....................................................... 4-2
CSR Access Window. .... ..... .... .......... ..... ... .... ....... ...... ..... .......... ........................ ... ... 4-4
DMVl1 Maintenance Loop Command Format. ..................................................... 4-24
Interrelationship Between Polling Parameters Q, R, and DELTA T ..................... 5-3
Relationship Between Polling Parameters Q, R, and the
'
Minimum Polling IntervaL.. .... ........ ... .... .... ........ ........ ........... .... .......... ....... ....... ...... 5-4
Relationship Between the Default Values for Q and R for the
Three Polling Activity Levels ................................................................................. 5-5
State Diagram of Polling State Transitions ..... ....................................................... 5-7
Data Link and Threshold Error Counters ............................................................... 5-10
Station Error Counters ............................................................................................. 5,;.,11
Data Memory Map ................................................................................................. 5-16
DMVl1 Linked List Structure Format. .................................................................. 5-17
Standard Link Block ..... ...... ............ ...... .... .......... ..... ..... ......... ....... .... ... ............. ... ... 5-1S
Global Status Slot ................................................................................................... 5-21
Tributary Status Slot.. ........ ............ ..... ..... ........... ........... ....... ........ ...... .... ......... ... ... 5-23
DMVII Block Diagram.......................................................................................... 6-2
Control and Address Decoder ......... ....... ... ......... .......... ... ........... ......... ............... ..... 6-3
I/O Data Bus .................................................................................................. ........ 6-4
USYRT Timing Diagram ....................................................................................... 6-5
Data Memory Organization .......... ................... ................................................. ...... 6-7
LSI-II Bus Interface .............................................................................................. 6-S
Integral Modem Receive. ............... ... ...... .......... ...... .......... .......... ..................... ...... 6-11
Integral Modem Transmit ....................................................................................... 6-12
Example of a Typical Isolation Flow Diagram ....................................................... 7-2
Data Link and Threshold Error Counters ............................................................... 7-8
Station Error Counters............................................................................................ 7-9

viii

FIGURES (Cont)
Figure No.
7-4
A-I
A-2
B-1
D-l
D-2
D-3
D-4
D-5
D-6
D-7
D-8

Title

Page

Full-Duplex Seven Tributary Multipoint Network ................................................. 7-14
DDCMP Data Message Format ..... ........................................................................ A-I
DDCMP Message Format in Detail ....................................................................... A-3
UNIBUS and LSI-II Address Map ....................................................................... B-2
Flow Diagram Symbology ....................................................................................... D-4
Modem Control (Start) ................... ........................................................................ D-5
Modem Control (Transmit)............. ........................................................................ D-6
Modem Control (Transmit 2) .................................................................................. D-7
Modem Control (Receive) ........................ ................ ......... ............... ...................... D~8
Modem Control (Modem Status)............................................................................ D-9
Modem Control (Call Timer) .................................................................................. D-I0
Modem Control (Shutdown) ................................................................................... D-ll

TABLES
Table No.
1-1
2-1
2-2
2-3
2-4
2-5
2-6
2-7
2-8
3-1
3-2
3-3
3-4
3-5
3-6
3-7
3-8
4-1
4-2
4-3
4-4
4-5
4-6

Title

Page

DMVl1 Options...................................................................................................... 1-3
DMVl1 Option Packing List .................................................................................. 2-2
Typical Host Options of a Bell 208A Data Set (4800 b Is)
Full-Duplex Operation ................................................................ ,........................... 2-5
Typical Tributary Options of a Bell208A Data Set (4800 b/s)
Full-Duplex Operation ............................................................................................ 2-5
DMVl1 Voltage Chart ........................................................................................... 2-6
Device Address Selectio·n... ................................. ....... ............ ....... .................... ...... 2-11
Vector Address Selection........................................................................................ 2-12
Cable Description ..........'......................................................................................... 2-14
Modem Option Jumper Functions .......................................................................... 2-30
SELO Bit Functions................................................................................................. 3-2
BSEL2 Bit Functions.............................................................................................. 3-4
Input Command Codes ........................................................................................... 3-5
Mode Field Codes and Functions............................................................................ 3-8
SEL6 Control Command Functions ........................................................................ 3-10
Request Key Field Definitions (Control Command) .............................................. 3-14
Output Codes .......................................................................................................... 3-21
Return Keys for Information Response .................................................................. 3-27
Diagnostic Error Codes ......................................... ................. ....... ............ .............. 4-5
User-Defined TSS Parameters................................................................................ 4-7
User-Defined GSS Parameters .............................................................. ~ ................ 4-12
Recommended Selection Interval Timer Values..................... ....... ........................ 4-15
Mode Switch Settings ............................................................................................. 4-23
Maintenance Command Functions BSEL2 Bits 0-3 ............................................... 4-25

TABLES (Cont)
Table No.
7-1
7-2
7-3
7-4
7-5
7-6

7-7
7-8
B-1
B-2
D-l

Title

Page

DMVII Diagnostics .................................. ,............................................................. 7-18
DMVII Static Logic Test Part 1 Diagnostic Summary ......................................... 7-18
DMVII Static Logic Test Part 2 Diagnostic Summary ......................................... 7-19
DMVII Static Logic Test Part 3 Diagnostic Summary ......................................... 7-19
DMVII Static Logic Test Part 4 Diagnostic Summary ......................................... 7-20
DMVII Static Logic Test Part 5 Diagnostic Summary ......................................... 7-21
DMVII Functional Diagnostic Summary .............................................................. 7-23
Microdiagnostic Error Codes .................................................................................. 7-24
Floating CSR Address Devices............................................................................... B-3
Floating Interrupt Vector Devices .................................................... ~..................... B-3
DMVII Modem Control Functions ........................................................................ D-2

PREFACE

This manual describes in detail the installation requirements, programming considerations and techniques, microcode operation, technical functions, and servicing procedures, including diagnostic support, for the DMVII Synchronous Controller. A variety of appendices are also provided to supplement
the above.
Other publications which support the DMVII Synchronous Controller are:

•

DMVll Print Set (MP-00942)

•

Electronic Industries Association (EIA) Specifications

•

DIGITAL Data Communications Message Protocol (DDCMP) Specifications (AA-D599ATC)

CHAPTER 1
INTRODUCTION

1.1 INTRODUCTION
The multipoint DDCMP-DMVII Intelligent Communications Synchronous Line Controller is a device
which provides efficient high-speed synchronous communications for distributed networks. The
DMVII uses LSI-II CPUs as control or tributary stations, while requiring a minimum of main CPU
resources. This manual provides detailed information necessary for installing and operating the
DMVII.
1.2 INTRODUCTION TO MULTIPOINT
Point-to-point configurations are practical when the message rate of the terminals is high. In many
cases, however, the message rate of the terminals is very low even though the bit rate may be quite
high. In these cases, sharing a transmission line can significantly reduce the cost and improve the efficiency of a communications network.
Various techniques are used to share transmission lines to improve their utilization. One of these techniques is the use of multipoint lines. In multipoint operation, a single line can be shared among many
nodes. Each node is a station and has a unique address. One station in the network is always designated
as the control station while the remaining stations are designated as tributary stations. Because all stations are connected to the same line, no two tributary stations may transmit at the same time, and each
station must have a means of recognizing which messages it is meant to receive. The address field of the
message header identifies the station to receive the message. The control station governs sharing of the
line by means of polling in order to authorize transmission to the control station. In a polling operation
the tributaries are in effect asked one by one whether they have anything to transmit. To accomplish
this, the control station sends a polling message with a unique tributary address down the line. The
station which recognizes the address responds by sending data or by sending a positive response.
Tributary stations can only transmit to the control station and only in response to a polling message
from the control station. Transmission between tributaries is not allowed as all message traffic must be
routed through the control station. Control stations on the other hand may transmit to any tributary at
any time if the communicating stations are in full-duplex. In fact, multiple messages for different destinations (tributaries) can be sent serially by the control station. Each tributary station then, in turn,
examines the address and accepts only those messages it is meant to receive.
The use of communication lines can be maximized by using full-duplex capabilities at the control station to accommodate many tributary stations on a full-duplex line. In this mode, the control station
keeps the lines full by sending to one or more tributary stations, while at the same time receiving from
another tributary station.

1.3 DMVll GENERAL DESCRIPTION
The DMVII is a high-performance line controller which operates at speeds up to 56K b/s. It accomplishes this by doing DMA transfers.
1-1

There are three available options and they are outlined below.
The DMVII-AA consists of:
•
An M8053-MA microcontroller/line unit (a quad-high module with multipoint microcode);
•

An H3254 (V.35 or integral modem) module test connector;

•

An H3255 (RS-423-A/232-C) module test connector;

•

A BC55H cable; and

•

An H325 and H3251 cable turnaround test connector.

The DMVII-AB consists of:
•

An M8053-MA microcontroller/line unit (a quad-high module with multipoint microcode);

•

An H3254 (V.35 or integral modem) module test connector;

•

An H3255 (RS-423-A/232-C) module test connector;

•

A BC05Z-25 cable; and

•

An H3250 cable turnaround test connector.

The DMVII-AC consists of:
•

An M8064-MA microcontroller/line unit (a quad-high module with multipoint microcode);

•

An H3254 (V:35 or integral modem) module test connector;-

•

A BC55F cable; and

•

H3257 and H3258 terminators.

These three options provide coverage of four different types of interfaces (see Table 1-1).
Features of the DMVII include:
•

Support of point-to-point and multipoint operation,

•

Support for remote or local, full-duplex, or half-duplex configurations,

•

Support for 12 tributaries and one control station in multipoint operation,

•

Switch and program selectable operating mode and tributary address,

•

Support for multiple addressed tributaries,

•

Down-line loading and remote load detect capabilities,

•

Go/No-Go diagnostic testing by the microcode,

•

Go/No-Go extensive error reporting,

•

Modem control.
1-2

Table I-I

DMVII Options

Option

Interface

Line Speed
(DMVII Limitations)

DMVI1-AA

EIA RS-232-C
EIA RS-423-A

Up to 19.2K bls
Up to 56K bls

DMVI1-AB

CCITT V.35

Up to 56K bls

DMVI1-AC

Integral modem

56K bls only

1.4 STANDARD APPLICATIONS
The DMVII can be used with the integral modem as well as with EIA and CCITT applications. These
applications can be configured as either point-to-point or multipoint networks. Figure 1-1 shows a typical point-to-point application and Figure 1-2 shows a typical multipoint application. For local operations
through integral modems, stations are interconnected by twinax or triaxial cables. The integral modem
can support up to 12 drops in both half- and full-duplex modes. For remote operations, stations are
connected through external modems that use common carrier facilities. For specific information on installation of either of the basic DMVl1 units and associated options, refer to Chapter 2.
For multipoint applications, the tributary address for each DMVII in the network is either switch or
program assigned. In the case of switch-assigned tributary addresses, specific switches on each DMVII
define the numerical value of the address to which that DMVII responds. The advantage of a switchassigned tributary address is that it provides data transfer security since the address cannot be changed
by software.
A major advantage of DMVII multipoint networks is the ability of the main CPU at the control station
to down-line load programs to the CPU at each tributary and start those programs without manual intervention. As a result, DMVl1-based multipoint networks are particularly suited for installation at
remote and generally inaccessible locations. For example, DMVl1s may be used in satellites, in hard to
reach locations such as weather stations at sea, and in hazardous environments.

1.5 DMVII SYSTEM OPERATION
Operation of the DMVl1 communications line controller is initiated and directed by a user program
residing in the main memory. The user program consistsof an application program and a device driver
that serves as an interface between the DMVII and the CPU.
Communication between the user program and the DMVl1 is accomplished over the LSI-II bus
through four control and status registers (CSRs). These four I6-bit registers serve as a bidirectional
port to pass user-program commands to the D MV 11, and D MV 11 responses to those commands back to
the user program. Each of these registers are word and byte addressable by both the user program and
the D MV 11 microcode.
NOTE
Normally only four CSRs are available to the user
program. However, in 22-bit address mode, eight
CSRs are available although only one additional 16'
bit register is used.
In this group of four CSRs, the first two have a fixed format and in general serve as a handshake control for user-program commands and DMVII responses. The next two CSRs form a port for the ex-

1-3

change of command and responses between the user program and the DMV 11. Other control fields
provide for initialization, interrupt enabling, reading and execution of maintenance instructions, data
transfer setup, and tributary addressing.
'
A user program issues a command to the DMVII by first requesting the use of the data port. When the'
DMVII grants permission to use the data port, the user program passes the cotnmand to the DMVII in
the CSRs. The DMVII interprets the command and performs the specified actions. If a response is
required, the DMVII stores the appropriate response in the CSRs and then informs the user program
that a response is present.

Message data received or to be transmitted by the DMVII is written into or read from preassigned
buffers in main CPU memory. These buffers are accessed by the DMVII througli non processor
requests (NPRs) to the associated bus address.

LSI-11 CPU

LOCAL
NODE

OPERATING
SYSTEM

USER PROGRAM
DEVICE DRIVER

REMOTE
NODE

LSI-" BUt:)

TRIB.

NOT
USED

I----t
~--t

r---,
r---"
-.----+.:L MODEM
:....!----..($ ---l.~1 MODEM I
___
L___ J
"S

-I

DMV11

~--t

#12

DMV11
MK·2485

Figure 1-1

DMVlls Used in Point-to-Point Applications

1.6 COMMAND/RESPONSE STRUCTURES
Since the DMVII is basically an input/output device, it follows that the command/response set for this
device be categorized as input commands and output responses. Input commands are commands issued
by the user program to the DMVII. Output responses are typically responses to those commands, and
are issued by the DMVII to the user program.
Some responses are unsolicited, and are used to inform the user program of protocol events and line
errors.

1.6.1 Input Commands
There are four types of input commands. They are listed below in the usual order of issuance.
I.
2.
3.
4.

Microprocessor control/maintenance,
Mode definition,
Control,
Buffer address/character count.

1-4

LSI·11 CPU
OPERATING
SYSTEM
USER PROGRAM/
DEVICE DRIVER '

DMV11
CONTROL
STATION
(INTERNAL
DATA
STRUCTURE)

TRIBUTARY
STATUS SLOTS
#2
#1

}

-.!!.....,

#12

r--'
I MODEM I

r---,

: MODEM
L __ ....J

DMV11
MULTIPOINT
NODE A
OPERATING
SYSTEM
USER PROGRAM/
DEVICE DRIVER

#1
STATUS SLOT
FOR SWITCH
SET TRIB.
ADDRESS
~

L __

r---,

....J

TRIB/STATUS
SLOTS FOR
MULTIADDRESS
STATION

DMV11
MULTIPOINT
NODE B
1----4

MULTIPOINT
NODE C
OPERATING
SYSTEM

I
L
__ ...JI

DMV11

OPERATING
SYSTEM

USER PROGRAM/

LSI.11 . B~ ...._D_EV_I_C_E_D_R_IV_E_R_......

I MODEM I

LSI-II

USER PROGRAMI
DEVICE DRIVER

MK-2520

Figure 1-2

DMVlls Used in Multipoint Applications

1.6.2 Output Responses

Output responses serve to inform the user program of normal or abnormal conditions concerning the
data transfer operation. There are three types of output responses:
1.
2.
3.

Control response,
Information response,
Buffer disposition response.

Figure 1-3 is a general summary of the functions performed by the DMVII command/response structure. These commands and response~ are discussed in detail in Chapter 3.

1.7 PROTOCOL SUPPORT
In DMVII point-to-point and multipoint networks, all message transfers between nodes are under control of the Digital Data Communications Message Protocol (DDCMP). All aspects of DDCMP processing are handled by the DMVII microcode. Message handling at the user-program level only involves
setting up data buffers during transmit operations and accepting data from the DMVII during receive
opera tions.
There are no file structure constraints on messages transmitted or received over DMV11 networks;
however, the maximum data message length allowed is 16,383 bytes. Also, there are no restrictions as
to the type of data transmitted or received under DDCMP since all data is transmitted and received in
transparent form.
There are basically three types of DDCMP messages: the data message, the control message, and the
maintenance message.

1.7.1

Data Messages

DDCMP data messages consist of two parts: the message header and the message body. The header
consists of eight bytes of control information necessary for successful transmission of the message. Included in these eight bytes is the block-check count (BCC) for the header, the byte count of the message body, and the tributary address. The header also contains two control bits; one that indicates resynchronization after this message, and one that controls line turnaround. The message body consists of
the message and a BCC for the message. Both BCC characters are used by the DMVII to validate
messages as they are received.
The header is assembled by the DMV11 and transmitted with the message body to form the data message. The receiving DMVII uses the header to verify the address and ensure that the message is received in the correct sequence. The header is also used to determine the number of bytes to transfer to
the user program. The header is discarded when the message is successfully passed to the user program.

1.7.2 Control Messages
Control messages are used to manage message traffic. They are eight-byte DDCMP messages which
are passed between control and tributary stations under sole control of the DMV11. Two examples of
control messages are acknowledge (ACK) and negative acknowledge (NAK). ACKs indicate successful
reception of messages while NAKs indicate unsuccessful reception. Control messages in multipoint also
contain the address field to identify the tributary to which the message is sent or received from.

1.7.3 Maintenance Messages
Under DDCMP, a DMVII has two data transfer modes: the DDCMP run state, and the DDCMP
maintenance state. In the run state, a DMVII receives and transmits data messages. In the maintenance state, a DMVII receives and transmits only maintenance messages. A maintenance message is
formatted much like a data message. It is formed by an eight-byte header followed by a variable length
message body. The content of the body is determined by the user program. Maintenance messages may
consist of: 1) operating or diagnostic programs transmitted by the control station for down-line loading
into the CPU of a specified tributary, or 2) a portion of the contents of a tributary's CPU memory as
requested by the control station. The request of this information is also handled by a maintenance message.

1-6

LSI·11
USER PROGRAM

USER PROGRAM ISSUES
MICROPROCESSOR CONTROL
COMMAND TO MASTER
CLEAR DMV11

INITIALIZE
DMV11

NOTIFY
USER
PROGRAM

FAILURE

USER
PROG. VERIFIES
INTERNAL
DIAG.
SUCCESSFUL,
DMV11 RUNNING

SET MODE TO HALF
OF FULL DUPLEX,
ESTABLISH STATION
AS POINT·TO·POINT
NODE OR MULTIPOINT
CONTROL OR TRIBUTARY
STATION

USER PROGRAM ISSUES
MODE DEFINITION
COMMAND

1
ESTABLISH TRIBUTARIES,
SET USER DEFINED
PARAMETERS, INITIATE
PROTOCOL STARTUP

USER PROGRAM ISSUES
CONTROL COMMANDS

ASSIGN TRANSMIT
AND.
RECEIVE BUFFERS

USER PROGRAM ISSUES
BUFFER ADDRESS /
CHARACTER COUNT
COMMANDS

TRANSMIT

RECEIVE

THE DMV11 PERFORMS THE FOLLOWING
RECEIVE MESSAGE FUNCTIONS:
1. PROCESS RECEIVE HEADERS
2. CHECK CRC's
3. ACKNOWLEDGE (ACK) PROPERLY
RECEIVED MESSAGES
4. NEGATIVE ACKNOWLEDGE (NAK)
ERRONEOUSLY RECEIVED MESSAGES

THE DMV11 PERFORMS THE FOLLOWING
TRANSMIT MESSAGE FUNCTIONS:
1. CREATE DDCMP MESSAGE
HEADERS
2. GENERATE MESSAGE AND
HEADER CRCs
3. TRANSMIT MESSAGES

j
THE DMV11 PERFORMS THE FOLLOWING
MESSAGE TRAFFIC CONTROL FUNCTIONS:
1. MESSAGE SEQUENCING
2. ERROR RECORDING AND REPORTING
3. PROTOCOL SUPPORT
4. LINK MANAGEMENT

DMV11 ISSUES BUFFER
DISPOSITION RESPONSES,
CONTROL RESPONSES AND
INFORMA TlON RESPONSES

MK·26S1

Figure 1-3

General Summary of DMVll Command/Response Structure

1-7

1.8 GENERAL SPECIFICATIONS
Environmental, electrical, and performance specifications for all DMV11 configurations are listed in
Sections 1.8.1 through 1.8.3.
1.8.1 Environmental Specifications
The DMVll is designed to operate in a class C environment as specified by DEC STD 102 (extended).
- Operating Temperature
- Relative Humidity

10% to 90% with a maximum wet bulb temperature of
28°C (82°P) and a minimum dew point of 2°C (36°F).

1.8.2 Electrical Specifications
The DMVl1 requires the following voltages from the LSI-II bus for proper operation.
Option

Voltage

DMVII-AA,AB

+5 V @ 3.4 A
+ 12 V @ 0.380 A

DMVI1-AC

+5V@3.35A
+ 12 V @ 0.260 A

A - 12 V @ 250 rnA required by the level conversion logic for both versions is generated off the + 12 V
by a switching inverter.

1.8.3 Performance Specifications
Performance parameters are as follows:
- Operating mode

Pull- or half-duplex

- Data format

Synchronous DDCMP

- Data rates

Up to 56K bls

- Tributaries supported

Up to 12

DMVlls may be connected to DMPl1s/DMV11s, DMRlls, DMC11s, and any other synchronous
controller running D DCMP protocol.

1-8

CHAPTER 2
INSTALLATION

2.1 INTRODUCTION
This chapter provides all the information necessary for a successful installation and subsequent checkout of the DMVII. Included are instructions for unpacking and inspection, preinstallation, installation,
and verification of operation.

2.2 UNPACKING AND INSPECTION
The DMVII is packaged according to commercial packing practices. When unpacking, remove all
packing material and check the equipment against the packing list (Table 2-1 contains a list of supplied
items for each configuration). Inspect all parts and carefully inspect the module for cracks, loose components, and separations in the etched paths. Report damages or shortages to the shipper and notify the
DIGITAL representative.

2.3 INSTALLATION CONSIDERATIONS
Installation of the DMVII microcontroller/line unit subsystem should be done in three phases:
•

Phase I - Preinstallation considerations
Verify system requirements, system placement, and configuration requirements.
Network topology chart
For multipoint networks it is absolutely necessary to know the configuration of the DMVll
(that is; control, tributary, HDX, FDX, and so on) locations of tributaries (w /address), and
where in network they are connected (control, Trib 187, Trib 98, Trib 208) or else troubleshooting will be extremely difficult.

•

Phase II - Microcontroller /line unit installation
Configure, install, and verify the microcontroller/line unit module via the appropriate diagnostics.

•

Phase III - DMVII system testing
Verify the DMV11 microprocessor subsystem operation with the functional diagnostics and
system exerciser programs.

2-1

Table 2-1
Option

DMVll Option Packing List

Parts List

Description

DMVII-AA

RS-232-C/RS-423-A interface containing:
M8053-MA
BC55H
H3254, H3255
H3251, H325
EK-DMVII-UG
MP-00942
ZJ328-RB

DMVII-AB

Basic remote DMVII unit
EIA RS-232-C/RS-423-A panel assembly
Module test connectors
Cable turnaround test connector
DMVl1 User's Guide
Field Maintenance Print Set
LIB kit
CCITT V.35 interface containing:

M8053-MA
BC05Z-25
H3250
H3254, H3255
EK-DMVII-UG
MP-00942
ZJ328-RB
DMVII-AC

Basic remote DMVl1 unit
CCITT V.35 cable
Cable turnaround test connector
Module test connectors
DMVll User's Guide
Field Maintenance Print Set
LIB kit
Integral modem interface containing:

M8064-MA
BC55F-I0
H3254
H3257/H3258
EK-DMVII-UG
MP-00942
ZJ328-RB

Basic local DMV 11 unit
Integral modem cable
Module test connector·
BC55A terminators
DMVll User's Guide
Field Maintenance Print Set
LIB kit

2.4 PREINSTALLATION CONSIDERATIONS
Table 2-1 and the following should be considered prior to ordering a DMVII communications interface
to ensure that the system can accept the DMVII and that it can be installed correctly. The steps should
also be verified at installation time.

It is strongly recommended that a topology diagram be drawn at installation time and maintained
throughout the life of the installation. Figure 2-1 shows a local network topology and Figure 2-2 shows a
remote network topology. The topology diagram should provide the following information.
Cable routing -

Show the actual physical location of the cable trough and indicate any equipment which might cause interference such as
an X-ray room.

Machine type -

Indicate whether the CPU is a PDP-ll/23, PDP-ll/70, PDP11/34, VAX-l1/780, and so forth. (The network could consist
of a mixture of DMPlls and DMVlls).

Type of station -

Indicate if the station is a control or tributary station.

Physical address -

DDCMP address can range from 1-255.

2-2

Location -

Indicate by room number or other appropriate means, the actual physical location of the equipment.

Node name-

The name given to the tributary if applicable.

Operating system and
version -

The name of the software operating system such as RSX-ll M
V3.2.

D ECnet version -

DECnet software version such as DECnet-ll M V3.0.

Transmit and receive -

Show transmit and receive lines. Depict end nodes and show
termination. If a patch panel is used, indicate the line numbers
between patch panels.

NOTE
The use of patch panels and numbering of the lines is
recommended.

I TX

ELEVATOR SHAFT

DELTA
11/70
DMP11
TRIB 3
RSTS XX.X
DE - Xx.x

SUSPENDED CEILIN G

ROOM 515

/I
II

I
RX

I
TX

II
GAMA
11/23
DMV 11
TRIB 2
RSX 11 M
DM - XX.X

BETA
11/34
DMP 11
TRIB 1
RSX11 M
DM - XX.X
ROOM 412

:::

ROOM 430

....

ALPHA
VAX 11/780
DMP 11
CONTROL
VMS XX.X
DV - XXX
ROOM 111
MK·2502

Figure 2-1

Local Network Topology

2-3

MERRIMACK
MK1 -1 /K37
VAX 11/780
VAX VMS XX.X
DV-XX.X
*NOTE 1
*NOTE 3
CONTROL
*NOTE 1
PATCH PANELS ARE
RECOMMENDED BUT MAY
NOT ALWAYS BE USED IFTHEY
ARE USED, THEIR'PHYSICAL
LOCATION SHOULD BE
INDICATED.

4800

NASH UA
EXCHANGE

4800

NASHUA
NU
11/60
RSTS XX.X
DE-XX.X
*NOTE 1
*NOTE 3

*NOTE 2
MODEM - 208A
CONTROL STATION OPTIONS
SEE TABLE 2- 2

TRIB 1

*NOTE 3
MODEM - 208A
TRIB'UTARY OPTIONS
SEE TABLE 2- 3

TEWKSBURY
TW

__- - I I

LOWELL
EXCHANGE

~ Ln VAX 11/750

VAX VMS XX.X
DV-XX.X
'
*NOTE 1
*NOTE 3
TRIB 2

4800

MARLBORO
MR
11/23
RSX-11 M
V.3.2
OM XX.X

MAYNARD
EXCHANGE

4800

4800
r--

MARLBORO

t-+-.... EXC HANGE
~NOTE 1 __

MAYNARD
PK3
11/23
RSX-' 1 M
V.3.2
*NOTE 1

*NOTE 2
TRIB 4

TRIB3

MK·2848

Figure 2-2

Remote Network Topology

2-4

Table 2-2

Typical Host Options of a Bell 208A Data Set (4800 b/s)
Full-Duplex Operation

Data' Set Options

DEC Recommended Settings

Transmitter timing

Data set (internal)

Carrier control

Continuous

Request-to-send operation in
continuous carrier mode

Continuous (CB constantly ON)

One second holdover at
receiver on ,line dropouts

Not provided

New sync-option to squelch
receiver clock

Not used - NS is strapped OFF
within the data set

Data set ready lead option
for analog loopback testing
by data terminal

CC is ON when the AL button (only)
is depressed

Grounding option

AB connected to AA

Table 2-3

Typical Tributary Options of a Bell 208A Data Set (4800 b/s)
Full-Duplex Operation

Data Set Options

DEC Recommended Settings

Transmitter timing

Data set (internal)

Carrier control

Switched (48.5 ms CA-CB delay)

Request-io-send operation in
continuous carrier mode

Continuous (CB constantly ON) NI A
Switched (8 ms ±.5 CA-CB delay)

N/A
One second holdover at
receiver on line dropouts

Not provided

New sync-option to squelch
receiver clock

Not used - NS is strapped OFF
within the data set

Data set ready lead option
for analog loopback testing
by data terminal

CC is ON when the AL button (only)
is depressed

Grounding option

AB connected to AA

2-5

.2.4.1 Device Placement
,
The DMVll can be installed in any LSI-II bus-compatible backplane such as H9276. On systems that
contain many high-speed direct memory access (DMA) devices, there is a probability of adverse bus
latency. To help prevent against this occurrence, the DMVll should be placed physically close to the
processor. As a result, this gives the DMVll a high DMA priority.

2.4.2

System Requirements
•

LSI-II bus loading
The MS053-MA or M8064-MA present two acloads and one dc load to the LSI-II bus.

•

Power requirements
Check the power supply before and after installing the microcontroller /line unit to ensure
against overloading. Power requirements are listed in Table 2-4.

•

Interrupt priority
The interrupt priority is preset to level four.

•

Device address assignment
The DMVll address .resides in the floating address space of the LSI-II bus addresses. The
ranking assignment of the DMVII for bus address is 24.
The selection of the device address is accomplished by switch packs on the microcontroller/line unit module. Refer to Figures 2-3 and 2-4.

• . Device vector address assignment
The DMVll vectors reside in the floating vector space of the LSI-II bus addresses. The
ranking assignment of the DMVll for vector assignments is 46.
The selection of the vector address is accomplished by a switch pack on the microcontroller/line unit module. Refer to Figures 2-3 and 2-4.

Table 2-4

DMV11 Voltage Chart

Module

Voltage Rating

Maximum
Voltage

Minimum
Voltage

Backplane
Pin

M8053-MA

+5 V @ 3.4 A
+ 12 V @ 0.380 A

+5.25
+ 12.60

+5.0
+ 11.40

AA2
AD2

M8064-MA

+5 V @ 3.35 A
+ 12 V @ 0.260 A

+5.25
+ 12.60

+5.0
+ 11.40

AA2
AD2

2-6

E113

E101

M8053

~
~

MK·2698

Figure 2-3

M8053 Switch Locations

2-7

I E119 II E107

,,'---c_ J 1_____

M8064

~
~

MK-2521

Figure 2-4

M8064 Switch Locations

2-8

2.5 INSTALLATION
When installing the DMVII in the LSI-II bus-compatible backplane, LSI-II configuring rules must
be followed.
Proceed with the installation as follows by performing the following on the slot that will contain the
DMVI1.
1.

Verify that the backplane voltages are within the tolerances specified in Table 2-4.

Turn system power OFF and perform resistance checks on the backplane voltage sources to
ground. This ensures that no short circuits exist. Refer to Table 2-4 for backplane pin assignments.

Configure the correct device address using switchpack settings from Table 2-5.

Configure the correct vector address using switchpack settings from Table 2-6.

Verify that the switch selectable features of the DMVII are configured for the station being
. installed. See Figure 2-5.

Insert the appropriate module test connector into the correct microcontroller jline unit connector as specified in Table 2-7. Be sure to insert the-test connector with "SIDE I" (etched
on the test connector) visible from the component side of the module. Refer to Figure 2-6 and
2-7.
Schematics and outline drawings of each test connector used with the DMVII are provided
in Figure 2-8.

Turn system power ON.

Load and execute the DMV11 static diagnostics. Five error-free passes of each part is the
minimum for successful operation.
(C)VDMA ** - DMVII static logic test part 1
(C)VDMB** - DMVII static logic test part 2
(C)VDMC** - DMVII static logic test part 3
(C)VDMD** - DMV11 static logic test part 4
(C)VDME** - DMVII static logic test part 5

Remove the module turnaround test connector and connect the appropriate cable (see Table
2-7 and Figure 2-9) to the proper Berg connector for the DMVII option selected. Refer to
Table 2-7 for detailed information on cable requirements and to Figures 2-10 through 2-14
for system cabling configurations.
NOTE
When installing panel cables BCssF or BCsSH, it is
important that the panel be properly mounted to the
rear-mounting bulkhead to ensure adequate grounding.

2-9

When connecting the BC55H connector panel, verify that the appropriate modem jumpers on
the panel are properly configured for the option selected. Table 2-8 lists each of these options
and required jumper configurations.
Integral modem options require that a 75 ohms terminator be connected to each receive line
(BC55F panel) at each end of a full-duplex and a half-duplex network. These terminators are
available in both male (H3257) and female (H3258) types to accommodate different integral
modem cabling. Selection of the appropriate terminator type is dependent upon which type
of unused panel connector is available on the receive line atJhe BC55F panel. Refer to Figure 2-10 for DMVII remote cabling and to Figure 2-11 for DMVII to DMVII local cabling.
10.

Insert the appropriate cable turnaround test connector in the end of the cable. Refer to Table
2-7 for the specific test connector. Load and execute the static di'lgnostics specified in Step 8
using the external maintenance mode selected to verify the module and cable. Upon obtaining a minimum of five error-free passes, proceed to the DMVII system test procedures, Section 2.6. Figure 2-8 illustrates the various test connectors used in the DMVIl.

2.6 DMVII SYSTEM TESTING
The final step in the installation of a DMVII subsystem is to exercise the DMVII as: 1) a unit on the
LSI-II bus; and 2) a link in a communications network.
2.6.1 Functional Diagnostic Testing
Ensure that the specific cable turnaround test connector for the selected DMVII option is still installed
at the end of the cable. Load and execute the DMVII functional diagnostics with the external mode
selected. Upon obtaining a minimum of five error-free end passes, proceed to Section 2.6.2.
2.6.2 DEC/XII System Exerciser
The DEC/XII system exerciser for the DMVII can be run in two different operating modes, internal
and external. The internal mode selects faster LSI-II bus activity. The external mode requires that the
spec~fic modem test connector be installed at the end of the cable. This is the preferred mode of operation. There are two DEC/XII modules for the DMVII; DMD* and DME*.
2.6.3 Final Cable Connections
The final step in the installation process is to return the DMVII to its normal cable connections, either
to the appropriate modem or to the distribution panel. The DMVII system cabling diagrams in Figures
2-10 through 2-14 have been included to help show overall cabling for the various DMVII-XX options.
References to specified locations of the various test connectors during diagnostic testing are also included. After the cables are connected to the appropriate modem or distribution panel, it is suggested that
the data communications link test program (DCLT) be exercised.
2.6.4 DMVII Link Testing
The DMVII can be exercised over a communications link by the data communications link test
(DCLT). It is suggested that DCLT he configured to run first on a cable test connector and then on a
modem with the modem analog loopback test feature selected (if the modem includes this feature).
Next, the overall communications link should be exercised with the remote computer system that contains a DMVII.

2-10

Table 2-5 Device Address Selection
MSB
15

12 111 110 1 9

I
I

SWITCH
NUMBER

I 8 I7 16 I 5

M8053 E53 M8064 E 58
I
I
I
I
I

I
I
•
S8
S7 S6 S5 S4 S3 S2
I

LSB
0

M8053
0
E54
M8064 I
E59
I

I
I

92
ON

ON
ON

760020

760060
760100

----760300
--760400
--760500
---

760600
ON

---

760700

----762000
---

761000

763000

ON
ON

DEVICE
ADDRESS

760200

ON
ON

760040

ON
ON

---

764000

NOTE: SWITCH ON RESPONDS TO LOGICAL ONE ON THE BUS
MK·2564

2-11

Table 2·6 Vector Address Selection
MSB
15

•
S8

1 1
5

M8053 E54
M8064 E59

•
SWITCH
NUMBER

1 6

ON
ON
ON
ON
ON
ON
ON
ON

•
S4

ON
ON
ON
ON
ON
ON

ON
ON
ON

ON
ON

LSB
0

1/0

VECTOR
ADDRESS
300
310
320
330
340
350
360
370
400

...

500

...

600
ON

...
...

700

NOTE: SWITCH ON PRODUCES LOGICAL ONE ON BUS
MK·2S63

2-12

765432
DDCMP ADDRESS REGISTER
TRIBUTARY/PASSWORD
ZERO = "ON"

E 119 (MS064)
E 113 (MS053)

MODE WHEN SWITCH
ONE IS SET

REMOTE
AUTO
LOAD
ANSWER
DETECT POWER
ENABLE ON

UNIT
NUMBER
FOR
BOOTING

MODE
ENABLE

BOOT
ENABLE
ZERO = "ON"

E 107 (MS064)
E 101 (MS053)

S
ON
ON
ON
ON
OFF
OFF
OFF
OFF

7
ON
ON
OFF
OFF
ON
ON
OFF
OFF

SWITCH SETTING FOR THE MODE OF OPERATION.
HDX PT TO PT DMC COMPATIBLE
FOX PT TO PT OMC COMPATIBLE
HDX POINT TO POINT
FOX POINT TO POINT
HOXCONTROL STATION
FOX CONTROL STATION
HDX TRIBUTARY STATION
FOX TRIBUTARY STATION

6
ON
OFF
ON
OFF
ON
OFF
ON
OFF

"ON" = V.35
"OFF" = EIA
MS053.

HIGH SPEED SWITCH
MUST BE SET
FOR INTEG RAL
MODEM OR WHEN
RUNNING ABOVE 19.2KB

HIGH
SPEED

* ON
UNUSED

E 107 (MS064)
E 101 (MS053)
OFF = "LOGIC ONE"

MS064
ZERO = "ON"
MK·2493

Figure 2-5

DMVII Switch Selectable Features

2-13

Table 2-7 Cable Description

Interface

Cable

RS-232-C

BC5SH
Refer to
Figure 2-9
View A

Module
Connector

Test
Connector

J2
(M8053)

H325

A cable with a 40-pin
Berg connector atone
end. The other end
has a panel that includes two different
cinch connectors, J 1
and J2. Connector J2
is used for RS-232-C
to connect to the
modem with external
cable BC05D-25. The
panel is mounted to
a rear-mounted bulkhead to ensure proper
grounding and ease of
access to external
cable connections.

H325

A 7.6 m (25 feet)
external cable that
connects to J 2 of the
BC5SC panel and an
RS-232-C modem.

H3251

Same cable as used
for RS-232-C except
that panel connector
J1 is used with external cable BC5SD-33
for connection to the
modem. The panel is
mounted to a rearmounted bulkhead to
ensure proper grounding and ease of access for external
cable connections.

H3251

A 10.1 m (33 feet)
cable that connects
to J1 of the BC55H
panel and an RS-449
modem.

BCOSD-25
Refer to
Figure 2-9
ViewB

RS-423-A

BC55H-03
Refer to
Figure 2-9
View A

J2
(M8053)

BC55D-33
Refer to
Figure 2-9
ViewC

2-14

Description

Table 2-7 Cable Description (Cont)
Module
Connector

Test
Connector

BC05Z-25
Refer to
Figure 2-9
View 0

Jl
(M8053)

H3250

A 7.6 m (25 feet)
modem cable with a
40-pin Berg connector
at one end that connects to J 1 of the
M8053. A 34-pin DataPhone 0 I G IT AL Service
(DDS) connector is
installed at the
other end and connects to the modem.

BC55F
Refer to
Figure 2-9
View F

J1
(M8064)

Panel
switch to
HDX position

A 0.9 m (3 feet)
cable with a 40-pin
Berg connector at one
end that plugs into
J 1 of the M8064. The
panel assembly is installed at the rearmounted bulkhead for
ease of external connections and to ensure proper grounding. '

Interface

Cable

V.35

Integral
Modem

Description

Appropriate terminator connectors H3257
or H3258 must be
used. See Figures 2-9
and View F.
Integral
Modem

BC55N-98
Refer to
Figure 2-9
ViewE

Local link
BC55F panel

None

A 29.9 m (98 feet)
external twinax cable
used to interconnect
a DMPII or a DMRII to
a DMVII system for a
selected data rate of
56K b/s.

BC55M-98
Refer to
Figure 2-9
ViewE

None

A 29.9 m (98 feet)
external triaxial
cable used for the
same purpose as the
BC55N, but for data
rates ahove 56K his.
The DMVII-AC supports
data rates of 56K
b/s.

2-15

CONNECT CABLE BC05Z FOR V.35 INTERFACE

H3254
TEST CONNECTOR

H3255
TEST CONNECTOR

~
L.:.JJ

I~ ~
: .

CONNECT CABLE BC66H
FOR RS·232·C OR RS·423·A
INTERFACE.

J
M8053

MK·250S

Figure 2-6

Test Connector Insertion for the M8053

2-16

CONNECT BC65F
FOR INTEGRAL MODEM

H3254
TEST CONNECTOR

W
L..:JJ

M8064

MK·2699

Figure 2-7

Test Connector Insertion for the M8064

2-17

J1
NUll ClK +
REC ClK +
TX ClK +
NUll ClK REC ClKTX ClK TX DATA R DATA +
TX DATA +

R DATA
RTS

crs
REC ROY
TER ROY
DATA MODE

..
~

RECINT

E..E
~
T-T
'A

..
..

...

K-K
....

S
+

+
+

T
....

•V

..
..

D'p

SIDE 1

H3254

JJ
-"",

TXINT
RECINT
TXINT

I!P

HH
.-

N--N
.;..

FF
.....

M-M
......

VIEWA

H3254 MODULE TEST CONNECTOR (J1 ON M8053/M8064)
MK·2645

000

AUX ClK +
TX ClK DIFF +
RX ClK DIFF +

OBODOAOC

AUX ClK-

OFOJOEOH

TX ClK DIFF RX ClK DIFF-

OlONOKOM
OROTOPOS

TX DATA DIFF +
RX DATA DIFF +

OVOxO~OW
OZObOYoa
Od
Oc
OlO90hO P

TX DATA DIFF -

000

H3250

..
..

U
.-

....y

...V
W
....
-!

.Xp
....

R
S

..;.::

...

CDET
DTR

DSR

CTS
VIEWB

-..

RX DATA DIFFRTS

onOkOmOj

I
c

.ii.

F
....

H
:..:
E
A.

MK-2123

Figure 2-8

DMVll Test Connectors (Sheet 1 of 4)

2-18

SEND COMMON

-.~B

REC COMMON
TER IN SER

INCOMING CALL

+
DATA MODE +
SEND DATA +
REC DATA +
TER RDY

SEND DATAREC DATANULL CLK +

-..
r

T...T

SEC REC DATA

*
*

..
..

LOCAL LOOP

SIDE 1

...-R..R
-Y
-l;..L

TH2

TH1

+
+

H3255

N..,.N

-[)
P

...K
E
....

SEL STAND BY

A-A

STAND BY IND

+
+

C--C

TER RDY-

+
+

M--M

---

DATA MODE -

H-H

TEST MODE

REC ROY -

;;;;.

SEC CTS

CTS -

B-S
-...,;,:

SEC RTS

RTS -

'1..

REC ROY +

SEC SEND DATA

CTS +

*
*

-..;:

RTS +

SIGNAL RATE IND

:.;:

;"",0

REC TIMING -

SEL SIGNAL RATE

I...

E-E

SEND TIMING-

SIGNAL QUALITY

I
K....K

REC TIMING +

NEW SIGNAL

Z
F
.A.
.;..

SEND TIMING +

NULL CLK-

OJ)

VIEW C

M
:..;,;

....
pp
....
"

H
U
.....

H3255 MODULE TEST CONNECTOR (J2 ON M8053)

;.:

YJ.

NOT REQUIRED FOR DMV11
MK·2644

Figure 2-8

DMVll Test Connectors (Sheet 2 of 4)

2-19

J1
1

•~

SHIELD GROUND
SIGNAL RATE INDICATION

SEND DATA +

SEND TIMING +

...'6

REO DATA +

-~'7

REO TO SEND +
REO TIMING +

...9

CLEAR TO SEND +

LOCAL LOOP

DATA MODE +

12
:a
f3
a

TERMINAL READY +
RECEIVER READY +

REMOTE LOOP

INCOMING CALL
SIGNAL RATE SEL
TERMINAL TIMING +

11
A

•

115

'•-7

18
.....

•

TERMINAL IN SERVICE

DATA MODE·

...

REQ T!MING·
CLEAR TO SEND·

TERMINAL READY·
RECEIVER READY·
SELECT STANDBY
SIGNAL QUALITY

...

NEW SIGNAL
TERMINAL TIMING·
STANDBY INDICATION

SEND COMMON

I: :

23
...

REQ TO SEND·

~C )

REO DATA·

-..

•
2.,0

RECEIVE COMMON

SIGNAL GROUND

SEND TIMING·

TEST MODE

SEND DATA·

~C )

....
...

2s
30

H3251

31
.:-

32
33
34
...

VIEWD

35
36

-37
--

H3251 CAB LE TEST CONNNECTOR

MK·2746

Figure 2-8

DMVII Test Connectors (Sheet 3 of 4)
2-20

H325
SCE324
SCT
15
SCR

SECXMIT~
CUT TO TEST
NEW ~ SYNC
SIDE l '
•

SECRCV~
XMITDATA~

RCVDATA~

•••••••••• •••
•••• •• ••• •••

RS34
CS
CO
NEW SYNC---4~......
14......
H326
6
DATA SET RDY-_.......--1
CUT TO TEST*
NEW SYNC

VIEW E

DTR--I....___
20~
22......
RI_...__
H326 CABLE TEST CONNECTOR (BCSSe AND BCOSD)
MK·2124

Figure 2-8

DMVII Test Connectors (Sheet 4 of 4)

2-21

VIEW A
RS-232-C

RS·423·A

,--- )

(-,~

I ......,
I""• .1
•I
II •• I
II • •
I I • •I

c::::::::IW15
c::::::::I W16
c::::::::I W17
c:::::J W18
c:::::J W19
c:::::J W20

, .. ,

1('

I, • :
II : •

··•
··•

............."

\,----~

r.::=J
r.::=J
c::J
c::J
r.::=J
c::J

'. I

I '. I
II • •I
I '.
II • • I
II • •I
• II I
II\,I - ••
__

W1 c:::::J
W2 c:::::J
W3 c:::::J
W4 c:::::J
W5 r=::J
W6 c:::::J
W7 c:::::J
W8 c:::::J
W9 c:::::J

•

" -'
"---

C5
C6
C4
C3
C1
C2
W10 c:::::J
W11 c::::::J
W12 c::::J
W13 c::::J
W14c::::J

>
>

BC55H-3 (RS-232-C/RS·423-A) INTERFACE PANEL CABLE
MK·2656

VIEW B

25 PIN
CINCH

BC05D-25 (RS-232-C INTERFACE) MODEM CABLE

25 PIN
CINCH
MK·2746

VIEWC

37 PIN
CINCH

BC550-33 (RS-422-A/RS423·A INTERFACE) MODEM CABLE

Figure 2-9 DMVII Cable Drawings (Sheet 1 of 3)

2-22

37 PIN
CINCH

,
MK·2743

VIEW D

BC05Z·25 (V.35 INTERFACE) MODEM CABLE
MK·2744

VIEW E

BC55N TWINAX CABLE

m!eCCr---t---~6 y'-----~! ~
BC55M TRIAX C/(BLE

MK·2742

Figure 2-9

DMVll Cable Drawings (Sheet 2 of 3)

2-23

VIEW F
FEMALE CONNECTORS

BC55F (INTEGRAL MODEM) PANEL CABLE

MALE CONNECTORS
CONNECTOR PANEL
(FRONT VIEW)
MK·2848

H3258

H3257

TERMINATOR

TERMINATOR
MI(·2244

Figure 2-9

DMVII Cable Drawings (Sheet 3 of 3)

2-24

H325 (RS-232-C)
RS-232-C/423-A

MODEM
BC55D-33

H3251
J2 TEST
CONNECTOR
H3255

H3251 (RS-423-A)

V.35 INTERFACE
DDS
MODEM
BC05Z-25

M8053

J1 TEST
CONNECTOR
H3254

CABLE TEST
CONNECTOR
H3250

MK·2525

Figure 2-10

DMVll Remote System Cabling Diagram

2-25

FUL.L.-DUPL.EX
INSTALL 750
TERMINATOR
CONNECTOR (H3267)

*
BC55F

FOR 56K bps USE CABLE BC55N-98
MK-2491

HALF- DU PLEX

INSTALL 75f2
TERMINATOR
CONNECTOR (H3257)

BC55F

HDX/FDX SWITCH
MUST BE IN THE
HDX (up) POSITION
ON BOTH PANELS
M8064

INSTALL 75f2
TERMINATOR
CONNECTOR
(H3258)

BC55F

FOR56K bps USE CABLE BC55N-98

MK-2492

Figure 2-11

DMVll to DMVll Integral (Local) Modem Cabling Diagram (Point-to-Point)

2-26

HDX NETWORK

CONTROL
STATION

TERMINATOR
(H3257)
i-

I
I
I

BC55F

I
I
I
I

'--

R V XMIT
HDXO

-QFDXO

TRIBUTARY

I
BC55F

I
I
I
I
I

RCV XMIT
L_ -QHDXO

TRIBUTARY

r- -{)FDXO
I
BC66F

I
r
I

L-

. ( ) XMIT
HDXO

TRIBUTARY

FDXO
BC66F
MK·21504

Figure 2-12

Half-Duplex Multipoint Network (Control Station End Node)

2-27

FOX NETWORK
TERMINATOR
(H32S7)

CONTROL
STATION

TRIBUTARY

BC55F

TRIBUTARY

BC55F

NOTES:
SOLID LINE REPRESENTS
CONTROL STATION TRANSMIT TO
TRIBUTARY RECEIVE.
DASH LINE REPRESENTS CONTROL
STATION RECEIVE FROM TRIBUTARY
TRANSMIT.

TRIBUTARY

TERMINATORS
BOTH ENDS OFTHE TRANSMIT LINE FROM THE TRIBUTARIES NEED TERMINATION
IN ADDITION TO THE ONE TRANSMIT LINE FROM THE CONTROL STATION
MK·2506

Figure 2-13

Full-Duplex Multipoint Network (Control Station End Node)

2-28

FOX NETWORK

TRIBUTARY

rI
I
I
I
I
L..

RCV
XMIT
{)HDX

CONTROL
STATION

FDX

TRIBUTARY

BC55F

NOTES:
SOLID LINE REPRESENTS
CONTROL STATION TRANSMIT TO
TRIBUTARY RECEIVE.
DASH LINE REPRESENTS CONTROL
STATION RECEIVE FROM TRIBUTARY
TRANSMIT.

TRIBUTARY

TERMINATORS
SINCE THE CONTROL STATION IS NOT AN END MODE, THERE IS NEED TO TERMINATE TWO SETS OF
TRANSMIT LINES FROM THE CONTROL STATION, ADDITIONALLY BOTH ENDS OF THE TRANSMIT LINE FROM
THE TRIBUTARIES

MK-2505

Figure 2-14

Full-Duplex Multipoint Network (Control Station Inner Node)

2-29

Table 2-8 Modem Option Jumper Functions
FUTURE 0
X.21 BIS

. rrX.20B,S
//

I: !t);'W1$~ «!J~~«fj»~
~
s

23
21
11
23
16
14
12
21
4
15
17
18
19

25
24
25
24
1'3
25
1
2
3
5
6
7
8
20
22

rv~!I)
0

kI
~

....

i;j

.::t .::t '" '" '"
~~,.::t
tP ~ ~ ~ Q~/Q~/Q~

W1
W2
W3
W4
W5
W6
W7
W8
W9
W10
W11
W12
W13
W14
W15
W16
W17
W18
W19
W20
W21

IN
IN

# # ~ ~ ~"y ~ry ry "y 0
0

i;j

....

I::- I::- I::- I::-

....

c·

....

J.::.

IN
IN
IN

IN
IN

CH
CG

IN
IN

IN
IN
IN

IN.
IN

....

~C),) ~ry~

tv.

IN
IN
IN

~
tV

c·

....

I::-

Q"r 8 8 8 8 ~ ~ ~ t;:r ii;~ 8

....

IN
IN IN IN IN
NOT NORMALLY INSTALLED
IN
IN IN
IN

IN
IN
IN

IN
IN

CI
SBB
SBA
SCF

IN
IN
IN
IN
IN
IN
IN
IN
IN

IN
IN
IN
IN
IN
IN
IN

SCA

IN
IN

CA
08

111
110
126
SF
112
SF
SRD 119
SSD 118
SRR 122
140
RL
RS 105
ST 114
RT 115
141
LL
SRS 121

TM
TT

SB
SS
SCB SCS
MAKE BUSY
AA

BA
BB
CB
CC
AB
CF
CD
CE

SO
RD
c:;S
OM
SG
RR
TR
IC

142
113
117
116
121
101
103
104
106
107
102
109
108
125

MK-2725

2-30

CHAPTER 3
COMMAND AND RESPONSE STRUCTURES
3.1 INTRODUCTION
This chapter defines DMVII command and response formats in all necessary detail, and describes all
programming sequences relevant to DMVII operation in the network environment. The CSR command
structure and format of input commands and output responses, as well as data port descriptions, are
described in detail. Discussions include special programming techniques, user access to maintenance
mode, and user interpretation of status/error reporting.
3.2 COMMAND STRUCTURE
The DMV 11 command set is structured into two categories; input commands and output responses.
Brief overviews of input commands and output responses, including command codes and the handshaking requirements, are provided in this section.
Transfer of control and status information between the main CPU resident user program and the
DMVII is accomplished through four 16-bit control and status registers (CSRs). Input commands are
issued to the DMVII by the user program, and output responses are issued to the user program by the
DMVII.
NOTE
Normally only four CSRs are used, but in the 22-bit
address mode, eight CSRs' are available.
3.2.1 Control and Status Registers
Four 16-bit CSRs are used to transfer control and status information. These registers are both byte and
word addressable. The eight bytes are assigned addresses in the floating address space in the I/O page
as follows:
16XXXO, 16XXXl, 16XXX2, 16XXX3, 16XXX4, 16XXX5, 16XXX6, and 16XXX7.
For discussion, these byte addresses are designated byte select 0 through 7 (BSELO through BSEL 7).
BSEL 10 and BSEL 11 are only used in 22-bit address mode. BSEL 12 through BSEL 17 are not used by
the user/DMVll-command structure and are not referred to in this document.
The four word addresses are the even numbered locations and are designated select 0, 2, 4, and 6
(SELO, SEL2, SEL4, and SEL6). The CSR addresses are assigned to the floating address space. The
floating address ranking for the DMVII is 24 (See Appendix B). The relationship between the symbolic byte and word addresses for DMVII CSRs, and the actual CSR layout, is shown in Figure 3-1.
Figure 3-2 illustrates the fields in CSR bytes BSELO, BSEL2, and BSEL3 that comprise the fixed
format portion of both user-program commands and DMVII responses. This fixed format portion serves to identify the command/response type, address of the tributary that the command/response applies
to, and coordinate ownership of the CSRs between the DMVII and the user program. Detailed bit
descriptions of SELO and BSEL2 are provided in Tables 3-1 and 3-2 respectively.
The four bytes comprising SEL4 and SEL6 contain the fields pertinent to each user-program command
and DMVl1 response. Detailed descriptions of the SEL4 and SEL6 fields are presented in Sections 3.3
through 3.4.

3-1

B7
BSEL1

BSELO

SELO

BSEL3

BSEL2

SEL2

BSEL6

BSEL4

SEL4

BSEL7

BSEL6

SEL6

l __ B'::L~ _ L _ ~S~O_ _ J SEL10*
*SEL10 IS ONLY USED IN 22 BIT ADDRESS MODE
MK·2660

Figure 3-1

DMVII CSRs Byte and Word
Symbolic Addresses
7

5
T

6
I

, 5 , 4

BSEL3

3
r

RQI

, 2 , 1 , 0

TRIBUTARY ADDRESS

RDI

COMMAND/RESPONSE
FIELDS

BSEL7

COMMAND/RESPONSE
FIELDS
I
I

COMMAND TYPE
CODE

BSEL2
SEL2

BSEL4
SEL4
I

BSELO

ROO

o
lEI

lEO

BSEL5

, 2 ,

BSEL6
SEL6

o
MK·1636

Figure 3-2

Fixed and Variable Formatsfor Commands and Responses

Table 3-1

SELO Bit Functions

Name

Description

Interrupt
Enable In (lEI)

When set, this bit enables the DMVll, upon asserting RDI (bit 4
of BSEL2), to generate an interrupt to vector address XXO.

1-3

Reserved

Interrupt
Enable Out
(lEO)

5-6

Reserved

Bits
BSELO

When set, this bit enables the DMVll, upon asserting RDO (bit
7 of BSEL2), to generate an interrupt to vector address XX4.

3-2

Table 3-1

SELO Bit Functions (Cont)

Bits

Name

Description

Request In
(RQI)

This bit is set by the user program to request access to the data
port. It is cleared by the user program when the data port is not
required for further issuing of commands. The user program may
leave RQI set if successive requests for the data port are pending.

Maintenance
Request

When set, along with master clear (bit 14 of SEL4), this bit
causes the DMVII to enter the maintenance register emulation
seCtion of the microcode.

BSELI
8

NOTE
Detailed discussion of maintenance register emulation is presented in Section 4.8.
9-10

Reserved

Diagnostic
Mode

Reserved

Invoke P/MOP
Boot

When set, this bit allows diagnostic programs to change the mode
of operation of the DMVll using the mode definition command
to override the mode switches.

Invoke primary MOP mode. When set to one, this bit causes the
DMVII at this multipoint station to request that the control station initiate the primary MOP (maintenance operation protocol)
boot procedure. In point-to-point networks, a DMV 11 having this
bit set requests the other station to initiate the primary MOP
boot procedure.

NOTE
The master clear bit (bit 14) must also be asserted
to use invoke P /MOP.
14

Master Clear

When set, this bit initializes the DMVII. The clock is enabled
and the RUN flip-flop is set. Master clear is self-clearing.

Run

This bit controls running of the microprocessor. It is set by bus
initialization or master clear. When run is cleared the microprocessor halts.

3-3

Table 3-2 BSEL2 Bit Functions
Bits

Name

Description

0-2

Control/Response
Code

These bits define the type of input command or output response as follows.
'

Bits
2

Description
0

o0 0

Buffer address/character count
(RCV) command or buffer disposition (RCV complete) response

o0 1

Control command or control response

o 1 0

Mode definition command or
information response

o 1 1

Buffer disposition (RCV unused)
response

1 0 0

Buffer address/character count
(XMIT) command or buffer disposition (XMIT complete) response

1 0

Reserved

1 0

Buffer disposition (sent but not
acknowledged) response

1 1 1

Buffer disposition (not sent)
response'

22-Bit Mode

This bit when set indicates to the DMVII that the buffer address is in
the 22-bit format.

Ready In
(RDI)

RDI is the DMVII response to RQI, indicating to the user program
that it has control of the CSRs to issue a command. It is oleared by the
user program when the data port contains the input command. Clearing
RD I returns control back to the D MV 11.

5-6

Reserved

Ready Out
(RDO)

RDO is asserted by the DMVII to indicate that the data ports (SEL4
and SEL6) contain an output response for the user program. The user
program must clear RDO after it has read this information. Clearing
RDO returns the CSRs to the DMVII.

3-4

3.2.2 Input Commands Overview
In general, input com,mands provide the means for the user program to assign, receive, or transmit buffers to the DMVll. Detailed field descriptions and formats of each input command are provided in
Section 3.3
There are four types of input commands that can be issued to the DMVII for execution.
•
•
•
•

Microprocessor control/maintenance command;
Mode definition;
Control;
Buffer address/character count.

With the exception of the microprocessor control/maintenance command, input commands require an
identification code in the first three bits of BSEL2 (see Figure 3-2). These codes, which define each
command and variations of specific commands within the command set, are defined in Table 3-2 and
listed in Table 3-3.
NOTE
CSR addresses are expressed in octal.
Table 3-3

Input Command Codes
Binary Code(BSEL2)

Input Command Type

Bit

Mode definition

Control

Buffer address/character count
(receive)

Buffer address/character count
(transmit)

3.2.3 Output Responses Overview
Output responses provide a means for the DMVII to report various normal and abnormal (error) conditions concerning the data transfer operation. Three basic responses are provided:
•
•
•

Buffer disposition;
Control;
Information.

The buffer disposition response is used to return both used and unused buffers to the user program.
The control response is used to report error conditions concerning the microcontroller /line unit hardware, data link, physical link, or remote station. It also passes protocol information to the user.
The information response provides information requested by a control command from the user program.

3-5

3.3 DMVll INPUT COMMANDS
This section provides detailed descriptions of each input command. Command formats and data port
usages are illustrated and defined. User-program execution requirements, command variables, and action taken by the, D MV 11 in response to commands are discussed.

3.3.1 Microprocessor Control/Maintenance Command
This single byte command has two functions; to initialize and cause the DMV 11 to start running, and to
cause entry into the microcode maintenance loop when the maintenance request bit is set. At start-up
time under normal operating conditions, this is the first command issued by the user program in order
to initialize the DMV 11.
The format for the DMV 11 initialization register (BSEL 1) is shown in Figure 3-3. To set the master
clear bit and thereby cause entry into the DMV11 running mode, the user program moves a byte with
an octal value of 100 to BSELI. As a result, all condition-sensitive logic in the DMV11 is reset for startup, and the start-up diagnostic is executed. When the diagnostic completes satisfactorily, the run bit in
BSELI is set to one. This indicates that the DMV11 is running and the microcode is executing.
Figure 3-4 presents a flow chart describing how to initialize the DMVl1. A timeout counter is set to
avoid the possibility of the user program being caught in an endless loop in case the internal diagnostic
does not complete successfully.
7

654

MK-2513

Figure 3-3

Microprocessor Control/Maintenance
Command Format

3.3.2 Mode Definition Command
Functionally, the mode definition command is used to establish the hierarchy of a network and the
characteristics of the communications line serving that network. As shown in Figure 3-5, the mode definition command contains two fields; the command type code field in BSEL2, and the mode field in
BSEL6. The mode field contains a code defining the function to be performed by the command.
i

With the mode definition command, the user program:can designate the DMVII as a control station, a
tributary in a multipoint network, or as a node in a point-to-point network. In addition, the characteristics (half-duplex or full-duplex) of the physical communications line connecting the network can be
defined.
.
The actual mode field codes and the functions implemented by each code are listed in Table 3-4.
Under normal operating conditions, the mode definition command is issued by the user program at
start-up time (after the internal microdiagnostics have executed successfully and the run bit is set).
Network discipline requires that each DMVII in a nehvork issue a mode definition command that is
appropriate to the network. For example, in a half-duplex multipoint network comprised solely of
DMVlls:
1.

The user program at the control station issues a mode definition command with the mode
field set at four.

The user program at each tributary station issues a mode definition command with the mode
field set to six.

3-6

SET MASTER
CLEAR BIT
IN BSEL1
(~SEL= 10° 8 )

SET
TIME OUT
COUNTER
TO
> 0.5 SEC

DIAGNOSTIC
ERROR, EXIT
TO ERROR
CONTINGENCY

EXIT TO
COMPLETE
START UP

MK-1638

Figure 3-4

Initialization of the DMVll
3-7

This network discipline also applies to DMVl1 s operating in point-to-point networks with other
DMVlls, DMPl1s, DMCl1s, and DMRlls.
When tributary addresses are software assigned, the mode definition command must be used at the
control and tributary stations to configure the network and assign line characteristics.
The functions performed by the mode definition command can also be implemented by the mode selection switches on the DMVl1 module. The switches must be used to establish mode definition functions
when tributary addresses are switch assigned. The switch setting for performing the mode definition
functions corresponds to the BSEL6 codes listed in Table 3-4.
Once the type of station is set, it can only be changed by a master clear or a physical change in the
switches. If the type of station is switch assigned, a master clear has no affect. However, the switches
are overridden when the diagnostic mode bit (bit 3 of BSEL 1) is set and a mode definition command is
issued.
6

6
I

3
I

Ral

lEO

•

ROO

2
I

lEI
1
I
0
0
CMD .TYPE CODE

TRIBUTARY ADDRESS

BSEl3

RDI

BSEl5

.
I

BSEl7
15

•

BSEl2
SEL2
BSEl4
SEl4

•

MODE FIELD
I

BSElO

BSEl6
SEl6

MK-1639

BSEL6 Bit
Positions
2

0
0
0
0
1
1
1
1

0
0
1
1
0
0
1
1

0
1
0
1
0
1
0
1

Figure 3-5

Mode Definition Command Format

Table 3-4

Mode Field Codes and Functions

Line
Characteristics

Network
Configuration

DMCII-Line
Compatibility?

Half-duplex
Full-duplex
Half-duplex
Full-duplex
Half-duplex
Full-duplex
Half-duplex
Full-duplex

Point-to-point
Point-to-poin t
Point-to-point
Point-to-poin t
Control station
Control station
Tributary station
Tributary station

Yes
Yes
No
No

3-8

NjA
NjA
NjA
NjA

3.3.3 Control Command
This command is the primary means of controlling the operation of DMVll-implemented networks.
The format of the control command is illustrated in Figure 3-6.
At start-up time, the user program at the DMVl1 control station must issue one control command (establish tributary) for each tributary address supported in the multipoint network. This must be done
after issuing the microprocessor control and mode definition commands. This causes the microcode to
create a tributary status slot (TSS) in the DMVl1 data memory for each tributary in the network.
Similarly, the user program at each tributary must issue a control command (establish tributary) for
each tributary to be established at that station. This causes a TSS to be created at that station for each
tributary it establishes.
In point-to-point networks, a control command (establish tributary) must be issued at both stations. The
tributary address field in this case must be a one. This results in the creation of a single TSS structure
at each station.
The DMVII microcode at the control station and at all tributary stations uses these TSS structures to
coordinate protocol operation over the network between the control/tributary pair. User programs, at
the control station and at the established tributaries, access these structures to obtain operational information such as:
•
•
•
•

The number of messages transmitted and received;
The number of selection intervals and timeouts;
The number of reply timeouts; and
The number of various types of errors.

,6 , 5

RDI

ROO
1

BSEL7
15

II I I
1:

lEI

BSELO

1
0
0
CMD TYPE ~ODE

BSEL2
SEL2
BSEL4
SEL4

DATA
I

~~~

DATA

BSEL5

lEO

RQI

TRIBUTARY ADDRESS

BSEL3

3
I

LATCH
POLLING
STATE
UNLATCH
POLLING
STATE

I Ia

WRI READ/IREAD
TSS
TSS

"REQUEST KEY OR
TSS ADDRESS

~§~

BSEL6
SEL6
0

DISABLE
COMMON
BUFFER
POOL
ENABLE
COMMON
BUFFER
POOL
MK·1840

Figure 3-6

Control Command Format

3-9

At the start-up of tributary stations having multiple software assigned tributary addresses, the user program at each station issues as many control commands as there are established tributaries at that node.
However, in networks where tributary addresses are switch assigned, only one control command specifying the switch assigned address is required as part of the' start-up sequence. Any other nonzero tributary address in a control command is overridden by the switches.
The control command is also used by the user program at the control station to specify a unique set of
polling parameters for each tributary in the network.
During normal operation, the control station microcode can determine the polling level of any tributary
in the network and adjust the polling frequency of that tributary as necessary (see Section 5.2).
The control command permits the user program to perform a number of control functions using the
same command format. In general, each function implemented by this command requires issuing of a
single appropriately formatted control command. SEL6 is used to define the various functions of the
control command (see Figure 3-6). Table 3-5 provides a detailed description of each bit or field.
Table 3-5

SEL6 Control Command Functions

Bit Name

Description

0-4 Request Key

These five bits are encoded ,requests from the user program. When this field is
used, bits 5 through 7 must be cleared. Request keys are encoded as shown in
Table 3-6.

A control command with this bit set, allows the user program to read two consecutive locations (two bytes) of a tributary status slot (TSS) or global status
slot (GSS) without modifying it.

Read TSS/GSS

The TSS to be read is specified in BSEL3 and the location within the TSS is
specified in bits 0-4 of BSEL6. Notice that bit 5 is also set to indicate a read
GSS. To read a GSS location, BSEL3 is zero.
When the DMVII receives a control command to read a TSS or GSS location,
it passes the requested information to the user program through an information
response (see Section 3.4.3). However, the requested information is placed on
an internal queue before it is passed to the user program. As a result, the information requested may change before the user gets it. This is particularly true
for number of messages transmitted/received and selection intervals.
6

Read and
Clear TSS/GSS

A control command with this bit set, allows the user program to read and clear
specific locations in a TSS or GSS.
The TSS to be read is specified in BSEL3 and the location within the TSS is
specified in bits 0-4 of BSEL6. Notice that a read and clear command bit 6 of
BSEL6 is also set. This gives a base octal value of 100 to which the specific
TSS address is added. To read and clear a GSS location, BSEL3 is zero.
Only the error counter sections of the TSS (7-17 octal) and GSS (15-17 octal)
can be accessed with a read and clear command.

3-10

Table 3-5
Bit

Name

SEL6 Control Command Functions (Cont)

Description
Accessing any other locations results in a procedural error.
Valid octal values for BSEL6 for the read and clear function are listed below:
Octal Value

TSS Location

107
110
111
112
113
114
115
116
117

Data messages transmitted
Data messages received
Selection intervals
Data errors outbound
Data errors inbound
Local buffer errors
Remote buffer errors
Selection timeouts
Local and remote reply timeouts

Octal Value

GSS Location

115
116
117

Remote station errors
Local station errors
Global header blockcheck and
maintenance data blockcheck
errors
These errors are covered in
detail Section 5.3.

When the DMV11 receives a control command to read and clear a TSS or GSS
location, it passes the requested information to the user program through an information response, and then clears the location.
As in the case of the read TSS/GSS, the information is placed on an internal
queue and is subject to change before the user gets it. However, by reading and
clearing, the user can keep a cumulative total.
7

Write TSS

A control command with this bit set, enables the user program to write into specific locations in an associated TSS or

ass.

The TSS to be written into is specified in BSEL3 and the specific location withis specified in bits 0-4 of BSEL6. To write to a
locain the TSS or
tion, BSEL3 is zero.

ass

Notice that bit 7 of BSEL6 is also set to indicate a write TSS. This gives a base
octal value of 200 to which the specific TSS address is added.

3-11

Table 3-5
Bit

Name

SEL6 Control Command Functions (Cont)

Description
The data to be written is contained in BSEL4 and BSEL5. There are eight TSS
and five GSS parameters that can be written:

TSS PARAMETER

BSEL6

Transmit delay timer (XDT)

230

Initial polling urgency (Q) and
polling rate (R) for active
state

231

6.
7.

Initial polling urgency (Q) and
polling rate (RJ for inactive
state
Initial polling urgency (Q) and
polling rate (R) for unresponsive
state

233

No data message count (non-inact)
and unresponsive timeout count
(TO-UN RESP)

234

Dead timeout count (TO-DEAD)
and maximum message count (MMC)

235

Selection interval timing
counter

236

Babbling tributary counter

237

232

See Table 4-2 for details

BSEL6

GSS PARAMETER
1.

2.
3.
4.
5.

Number of sync-characters to
precede nonabutting messages

233

Preset value for streaming
tributary time counter

234

Polling algorithm update
interval (DELTA T)

235

Polling rate for dead tributaries (DEAD T)
Fixed polling delay (poll
delay)
See Table 4-3 for details

NOTE
Some parameters are 8-bits in length. Thus, in those
cases two parameters are indicated. All user accesses are on two byte boundaries.

3-12

236
237

Table 3-5

SEL6 Control Command Functions (Cont)

Bit

Name

Description

Enable
Common
Pool

A control command with this bit set allows a specified tributary (BSEL3) to use
the common receive buffer pool. Usage of the common pool is based on a common pool quota. This quota is determined for the specified tributary by adding
the octal value in BSEL4 to the current quota. If this results in a value equal to
or greater than 377 octal, a procedural error results and the quota is reset to
376. However, a tributary may be set up for unlimited use of the common pool
by setting BSEL4 to 377. Each time a tributary uses a common pool buffer, the
quota is decremented by one. When the quota reaches zero, the tributary is prevented from using the common pool. See Section 3.3.4 for more details on common buffer pool.
The common pool is checked first. If no buffers are available or the quota is
zero, or the buffer is too small, the private receive buffers are checked.

Disable
Common Pool

A control command with this bit set, disables the use of the common receive
buffer pool for the tributary specified in BSEL3.
The quota previously established for this tributary is cleared to zero.

lOII

Reserved

Unlatch Polling State

A control command with this bit set, causes the polling state level of the tributary addressed by BSEL3 to go to the active polling state. Control of the polling
activity for the specified tributary is then returned to the polling algorithm.

Latch Polling State

A control command with this bit set, establishes the polling state of the "tributary addressed by BSEL3. The polling state is determined by bits 0 and 1 of
BSEL4. These bits are encoded as follow:
Bits 1 & 0

Polling State

Active
Inactive
Unresponsible
Dead

01
10

3-13

Table 3-6

Request Key Field Definitions (Control Command)

Octal
Code

Name

Description

No Request

This code allows the issuing of a null control command for the purpose
of returning control of the CSRs to the DMV 11. The no request code
is used when RDI is set but there is no command to issue (sec Section
4.2.3). This is effectively an NOP command.
NOTE
The
enable/disable
common
pool
and/or
latch/unlatch polling state bits in. BSEL 7 can be
used in conjunction with this request key.

Establish
Tributary

This control function initiates the creation of the tributary status slot
(TSS) data structure. This must be accomplished before any command is issued that uses a tributary address.
The user program at the control station hlust issue one establish tributary control command for each tributary supported in the network.
The tributary address is designated in BSEL3.
NOTE
In a point-to-point network, this control command,
with a tributary address of one in BSEL3, should be
issued at each station to establish the required TSS.
The DMVll has 12 available TSS blocks. Each block has 64 - 8-bit
locations for storing status and other information necessary for maintaining communications over the data link.
As a result of establishing one or, more tributary addresses, the
DMVII creates a global status slot (GSS). This GSS is part of the
overall status structure at each station.
NOTE
This control command function can also be used
during normal operation of a multipoint network to
reestablish previously deleted tributaries. In such
cases, the tributary address must be reestablished at
both the control station and the pertinent tributary
station.
NOTE
The enable/disable common pool and / or the
latch/unlatch polling state bits in BSEL7 can be
combined with this control function in a single control command.

3-14

Table 3-6
Octal
Code

Request Key Field Definitions (Control Command) (Cont)

Name

Description

Delete
Tributary

This control function removes a specified tributary from operational
status by eliminating its associated TSS. Prior to issuing this command, the user program must first halt the tributary being deleted.
[See request key 05 (request halt state)]. The TSS can only be reestablished by using an establish tributary function. Only 12 addresses
may be established at anyone time.

Request Start-up
State

This control function initializes the designated TSS and initiates the
DDCMP start-up sequence for that tributary. BSEL3 specifies the tributary address. Request start-up state must only be issued to tributaries that"are in the halt state.
When the start-up sequence is completed, the DMVII notifies the
user program by issuing a control response. When this response (run
state) is received by the user programs at the tributary and control
station, message traffic can begin between these two stations (see
Table 3-7).

NOTE
The enable/disable common pool and/or the
latch/unlatch polling state bits in BSEL7 can be
combined with this control function in a single control command.

Request Maint
State

This control function places the tributary designated by BSEL3 into
the D DCMP maintenance state.
A tributary placed in the maintenance state can only transmit and receive maintenance messages. Both the control station and tributary
must be in the maintenance state in order for maintenance message
traffic to occur.
The maintenance state must only be issued to tributaries that are in
the halt state.

NOTE
The enable/disable common pool and/or the
latch/unlatch polling state bits in BSEL7 can be
combined with this control function in a single control command.

3-15

Table 3·6 Request Key Field Definitions (Control Command) (Cont)
Octal
Code
05

Name

Description

Request Halt
State

This control function places the tributary designated by BSEL3 into
the DDCMP halt state. All outstanding buffers are returned.
When a tributary is halted at the control station, the tributary is no
longer polled. When a tributary is halted by its own user program, it
no longer responds to polling.
The TSS for the halted tributary remains unchanged at both the control and tributary stations. The halted tributary can be restarted by
issuing a request start-up state control command.
NOTE
The halt state may also be used on a global basis to
return all common pool buffers. This is accomplished by using a tributary address of zero in
BSEL3 when issuing the request halt state.
Tributaries must not be using the common pool when
this function is issued. If the common pool is in use,
a procedural error of 136 is generated (see Table 37).

Read Modem
Control

This control function permits the user program to write the contents of
BSEL4 into the DMV11 modem register. (See Appendix C).

Write Modem
Control

This control function causes the DMVII to read the modem register
and pass this information to the user program through SEL4 by way
of an information response. (See Appendix C.)

NOTE
Request key codes 6-17 and 22-37 are reserved.

3.3.4 Buffer Address/Character Count (BA/CC) Command
This command provides the user programs at both the control station and tributaries with the means to
assign, transmit, and receive buffers.
The format for this command is shown in Figure 3-7. Note that the command has two forms to facilitate
separate management of transmit and receive buffers. These two forms are distinguished by the type
code in BSEL2. A type code of zero is used to allocate receive buffers and a type code of four is used to
allocate transmit buffers.
The tributary address is specified by BSEL3 and the buffer address is contained in SEL4 and bits 14
and 15 of SEL6. The remaining 14 bits of SEL6 contain the character count in positive notation. A
character count of zero is illegal.

3-16

In addition to allocating receive and transmit buffers, the buffer address/character count command is
used to allocate common receive buffers by specifying a tributary address of zero in BSEL3. These
buffers can only be used by tributaries authorized to do so by the enable common pool bit of a control
command.
When the user program has a message to transmit, it informs the DMVll of the size and address of the
message buffer. This is done by the buffer address/character count command on a one buffer per command basis. A tributary address of zero when assigning transmit buffers results in a procedural error.
When the user program is receiving messages, it assigns receive buffers on a one buffer per command
basis using the buffer address/character count command. These buffers may be in the common pool of
buffers or be private buffers. Each BA/CC command used to assign a buffer to be the common pool
must contain a zero in BSEL3. Although this command assigns buffers to a common pool, actual allocation is performed through the control command by enabling access to the common pool on a per tributary basis.

, 6 , 5 , 4 , 3

2
I

BSEL3

TRIBUTARY ADDRESS

BSEL5

BUFFER ADDRESS
HIGH BYTE

RQI

RDO

BSEL7

B/A
17

I I

B/A
16

CHARACTER COUNT
~IGH SIX BIT~
12

9
8
7
6
18 BIT ADDRESS MODE

BSEL4
SEL4

CHARACTER COUNT
I LOW BYTE j

BSELO
BSEL2
SEL2

BUFFER ADDRESS
LOW BYTE

lEI

CMD TYPE
,CODE,

RDI

lEO

, 2 ,

, 5
,

BSEL6
SEL6

MK-1641

7
7

6
I

BSEL3

BSEL11

RQI

•

CHARACTER COUNT
HIGH SIX BIT~
12

I
I

lEI

BSEL4
SEL4

BSEL6
SEL6

BUS ADDRESS BITS 16-21
J

CHARACTER COUNT
J
LOW. BYTE

BSELO
BSEL2
SEL2

CODE~

BUFFER ADDRESS
--'- LOW pYTE

UNUSED

CMD TYPE

MODE

UNUSED

22BI~1

RDI

lEO

RDO

--'-

BUFFER ADDRESS
HIGH BYTE

BSEL5
BSEL7

3
I

TRIBUTARY ADDRESS

BSEL10
SEL10

22 BIT ADDRESS MODE
*TYPE CODES
BUFFER ADDRESS/CHARACTER COUNT COMMAND - RECEIVE = 000
BUFFER ADDRESS/CHARACTER COUNT COMMAND - TRANSMIT
100

MK-2512

Figure 3-7

Buffer Address/Character Count Command Format

3-17

In multipoint networks, user programs at both the control and tributary stations can handle allocation
of receive buffers in two ways:
1.

The first method involves the allocation of receive buffers from a common pool of buffers.
With the common buffer pool enabled, receive buffers are assigned to the pool through the
buffer address/character count command on the basis of one buffer for each command issued. Each buffer address/character count command used to assign a buffer to the common
pool must contain a zero in BSEL3. Although this command assigns buffers to a common
pool, actual allocation to a tributary is done through the control command by enabling access
to the pool and assigning quotas (see Table 3-5).

In the second method, the user program can directly allocate private receive buffers based on
anticipated message traffic using one buffer address/character count command for each private buffer allocated. In this context, a private buffer is defined as a receive buffer assigned
to a specific tributary for its exclusive use, and in all cases the address of that tributary must
be in BSEL3 of the assigning command.

Private buffers and buffers from a common pool can be used jointly at control and tributary stations in
a multipoint network. Under these circumstances, the advantages provided by both methods are available to the user program.
Private buffers can be set for unanticipated messages and/or abnormally large messages.
The preceding information involved standard 18-bit addressing. However, the DMVII may also operate in 22-bit addressing mode. The DMVII allows the software to set th~ 22-bit address mode of operation. The bit indicating 22-bit address mode is set by the user program as part of a command when
issuing transmit or receive buffers to the DMVII. The state of this bit is retained to indicate to the
. DMVII the number of bits in the buffer address.

3.4 DMVll OUTPUT RESPONSES
The DMVII microcode has a set of three responses it can use to either reply to user-program commands or to inform the user program of error conditions. These responses are:
•
•
•

Buffer disposition response;
Control response;
Information response.

As with input commands, each output response is identified by a typecode in bits zero, one, and two of
BSEL2.

NOTE
In multipoint networks, each response issued contains (in BSEL3) the address of the tributary that
relates to the response. However, in point-to-point
networks, equivalent responses always contain a one
in BSEL3.

3-18

3.4.1 Buffer Disposition Response
This response is used to return both used and unused buffers to the user program. Figure 3-8 shows the
format of this response and identifies the five methods of message disposition in BSEL2. BSEL2 bits
zero, one, and two are encoded as follows:
Bit2

Bitt

BitO

Buffer Disposition

0
0
1
1
1

0
1
0
1
1

0
1
0
0
1

Receive buffer complete
Receive buffer unused
Transmit buffer complete
Transmit buffer sent but not acknowledged
Transmit buffer not sent

Receive Buffer Complete - When a message is received successfully and stored in the assigned main
memory buffer, the DMVII microcode notifies the user program" by issuing a buffer disposition response with a type code of 000. Data in the receive buffer is not valid until such a response is issued.
This response is issued for both common pool and private buffers.
Receive Buffer Unused - When the protocol for a specified tributary is halted, the DMVl1 automatically returns all associated private receive buffers to the user program. To do this the DMVl1 issues a
buffer disposition response with a type code of 011 for each outstanding buffer held by the specified
tributary. This pertains to private buffers only.
7

BSEL3

BSEL5

2
I

1
I

RQI

lEO

ROO

RDI

CMD TYPE
CODE*

CHARACtER COUNT
HIGH SIX BITS
13

BUFFER ADDRESS
, LOW BYTE

•

9
8
7
6
18 BIT ADDRESS MODE

6
I

BSEL5

BSEL11

,•

•

. 2

MK·1842

lEI

I3SELO

CHARACTER COUNT
HIGH SIX BITS

UNUSED
•

RDI

9
8
7
6
22 BIT ADDRESS MODE

BSEL6
SEL6

22BIT
MODE
1

I
CMD TYPE

CODE~

BUFFER ADDRESS
LOW BYTE

•

...L

ROO

UNUSED

lEO

BSEL2
SEL2

UNUSED

BSELO

RQI

BUFFER ADDRESS
• HIG~ BYTE.

lEI

BSEL4
SEL4

CHARACTER COUNT
LOW BYTE I

TRIBUTARY ADDRESS

BSEL3

BSEL7

BUFFER ADDRESS
HIGH BYTE
B/AI
16

TRIBUTARY ADDRESS

B/A
17

BSEL7

2
I

BSEL4
SEL4

BSEL6
SEL6

BUS ADDRESS BITS 16-21
•

CHARACTER COUNT
• LOW, BYTE~

•

BSEL2
SEL2

BSEL 11
SEL10

* BUFFER DISPOSITION RESPONSE TYPE CODES:
1. RECEIVE BUFFER COMPLETE = 000
2. RECEIVE BUFFER UNUSED = 011
3. TRANSMIT BUFFER COMPLETE
100
4. TRANSMIT BUFFER SENT NOT ACK'd = 110
5. TRANSMIT BUFFER NOT SENT
111

=
=

MK·2515

Figure 3-8

Buffer Disposition Response Format

3-19

The DMV 11 returns all common pool buffers if the user program issues a request halt state control
command with a tributary address of zero. When all common pool buffers are returned, the DMVll
issues an information response indicating that the process is finished.
Transmit Buffer Complete - When a message is transmitted successfully, the DMVl1 notifies the user
program by issuing a buffer disposition response with a type code of 100. Successful transmission
means that the receiving station has acknowledged receipt of the message.
Transmit Buffer Sent But Not Acknowledged - When the protocol for a specified tributary is halted, the
DMVII automatically returns all transmit buffers currently being processed by that tributary to the
user program. To do this, the microcode issues a buffer disposition response with a type code of 11 G for
each buffer sent but not acknowledged.
NOTE
During protocol operation, after seven unacknowledged transmissions of a message occur, the transmit threshold error is exceeded and the DMVll issues a control response indicating this error (see
Section 3.4.2). The DMVll continues to retransmit
the message and responsibility for terminating the
transmission belongs to the user program.
Transmit Buffer Not Sent - DMVll maintains a queue of buffers to be transmitted for each tributary
address established in the network. When the protocol for a given tributary is halted, the DMVII returns all unused buffers in the associated queue to the user program. To do this, the DMVII issues a
buffer disposition response with a type code of III for each transmit buffer remaining in the queue.
The o'ther CSRs used by the buffer disposition response are BSEL3, SEL4, and SEL6. The function of
these CSRs is as follows:
•

BSEL3 specifies the tributary address associated with the buffer disposition response.

•

SEL4 and bits 14 and 15 of SEL6 contain the I8-bit buffer address for the buffer being
completed or returned. For 22-bit address mode, bits 0-5 of BSEL6 are used with SEL4.

•

SEL6 (or SELIG in 22-bit address mode), bits zero through 13, compose a I4-bit character
count allowing for a maximum buffer size of 16,383 bytes. A character count returned by a
buffer disposition response is designated in positive binary notation.

Protocol is halted for a tributary in one of three ways when:

The user program issues a control command halting the tributary.

A DDCMP STRT message is received while the tributary is in the run state.

A DDCMP maintenance message is received, temporarily halting the protocol, while receive
buffers are being returned.

3.4.2 Control Response
A control response is an unsolicited response issued by the DMVII when an error is detected or when
protocol information must be passed to the user program. The format for the control response is shown
in Figure 3-9. BSEL3 contains the tributary address or character count, SEL4 and bits 8 through 13 of
SEL6 contain the bus address for the affected buffer, and BSEL6 indicates the type of information
being passed to the user program. In 22-bit address mode, SEL6 contains buffer address bits 16-21 and

3-20

BSEL 10 indicates the type of information being passed to the user program. These types of information
are indicated by an octal code and are listed in Table 3-7. Basically there are four categories of information.
1.
2.
3.
4.

System events
Protocol events
Network errors
Procedural errors
Table 3-7

Octal
Code
002

Output Codes

Category

Information

Network
Error

Receive threshold error - This error is reported to the user program when the
number of consecutive receive errors equals seven. These receive error types
are:
1.
2.
3.
4.
5.
6.
7.

Message header blockcheck.
Message data blockcheck.
NAK in response to a DDCMP reply message.
Buffer temporarily unavailable.
Receive message overrun.
Message header format error.
When a message is too long for the
available buffer.

Each time the receive threshold error is reported, the counter is reset to zero.
004

Network
Error

Transmit threshold error - This error is reported when the number of consecutive transmit errors equals seven. These transmit errors consist of four
types and occur when:

A STRT message is transmitted but not acknowledged within the timeout

A STACK message is transmitted but not acknowledged within the

period.

3.
4.

timeout period.
ANAK is received in response to a transmission with a reason code other
than REP response.
A data message is transmitted but a reply was not received within the
timeout period.

Each time a transmit threshold error is reported, the transmit error counter is
reset to zero, except when remaining in the DDCMP ISTRT and ASTRT
states.
006

Network
Error

Select threshold error - This error is reported when the selection interval timeout counter for a given station has timed out seven times. The selection interval is the time allocated for a tributary to respond to a poll or for a point-topoint station to respond to a transmission.
Each time the select threshold error is reported, the selection error counter is
reset to zero.

3-21

Table 3-7
Octal
Code

Category

Output Codes (Cont)

Information
NOTE
For more information on receive, transmit, or selection threshold errors, see Section 5.3.3.

010

Protocol
Event

Start message received while running - This response indicates that a
DDCMP STRT message was received from the station specified in BSEL3
while this station was in the DDCMP run state.
In normal operation, this message is used by a control station to inform a tributary that the control station has started protocol operation for that tributary.
The start message is also used to resynchronize the logical link between a control station and tributary. This might be necessary when message traffic is inhibited because of threshold errors or receive or transmit overruns.
When the DDCMP STRT message is received: 1) the DMVll responds with
start message received while running, and 2) the protocol at the tributary halts
and all buffers are returned.
At this time the logical link may be restarted (request start-up state control
command).

012

Protocol
Event

Maintenance message received while running (or ISTRT or ASTRT) - This
response indicates that a DOCMP maintenance message was received by a
specific tributary while it was in the OOCMP run, ISTRT, or ASTRT state.
This causes the tributary to notify the user program, return all unused buffers
to the user program, and halt the protocol. The 0 MV 11 then places the tributary in the maintenance state. The message that caused this event is lost.

014

Protocol
Event

Maintenance message received while halted - This response indicates that a
ODCMP maintenance message was received by a specific tributary while it
was halted. This places the tributary in the maintenance state. The message
that caused this event is lost.

016

Protocol
Event

Start message received while in the maintenance state - This response indicates that a DOCMP STRT message was received by a specific tributary
while it was in the maintenance state. No further action is taken by the microcode. The user program determines what action to take based on this response.

022

System
Event

Tributary polling state dead - This response informs the user program at a
control station that the specified tributary polling state has gone to the dead
state.
This response has no meaning in point-to-point networks.

3-22

Table 3-7
Octal
Code

Output Codes (Cont)

Category

Information

024

Protocol
Event

Run state - This response informs the user program at all stations that a specific tributary has entered the run state. The DMV 11 microcode issues this
response as a result of receiving a request start-up state control command and
having completed the DDCMP start-up sequence.

026

Network
Error

Babbling tributary - This response is issued to a user program to record the
occurrence of a babbling tributary. It is only used by half-duplex point-to-point
and multipoint control stations.
A babbling tributary is one which continues to transmit valid control messages
or message headers beyond the end of a programmable timeout (babbling tributary timeout counter).
The babbling tributary response usually indicates a malfunction at the transmitting station or too short a period for- the timeout counter.
Recovery from this error condition generally requires human intervention at
the remote station.

030

Network
Error

Streaming tributary - This response is issued to a user program to indicate
that the remote station failed to release the channel at the end of the selection
interval. It is only used by half-duplex point-to-point and multipoint control
stations.
The streaming tributary timeout period is determined by the programmable
streaming tributary timeout counter. The timeout period starts at the end of
the selection interval.
This error condition generally indicates a modem malfunction at the remote
station or an inappropriate choice of the streaming tributary timeout counter.
Recovery from this error condition generally requires human intervention at
the remote station.

32-76

Reserved

100-276 Procedural
Error

Procedural errors - This response is issued by the DMVII when the user program violates the procedures designated for interfacing the DMVII. In all
cases, the event that caused the procedural error is ignored by the microcode.
All procedural errors except octal codes 140, 300, and 302 are reported immediately to the user program. Those procedural errors are placed on the response queue. Specific procedural violations are identified by the octal code in
BSEL6 as follows.

3-23

Table 3-7 Output Codes (Cont)
Octal
Code

Category

Information
Code

Description

100

A command other than a mode definition command is issued before
the mode has been established.

102

Invalid type code used in a command.

104

Invalid mode change (for example, the mode of a tributary station is
changed to point-to-point).

106

A nonglobal command is issued to an unestablished tributary.

110

A nonglobal command is issued having a tributary address of zero.

112

Attempt to delete or place an unhalted tributary in the start or
maintenance protocol state.

114

Attempt to establish more than 12 tributaries.

116

Attempt to establish an already established tributary.

120

An invalid request key is used in a control command.

122

Attempt to assign a buffer for an unestablished tributary.

124

Attempt to assign a buffer for a halted tributary

126

Attempt to assign a buffer having a byte count of zero.

130

Attempt to assign a transmit buffer with a tributary address of zero.

132

Attempt to write or read and clear a reserved area of a tributary or
global status slot.

134

Attempt to use the reserved bits in BSEL7 of control command.

136

Attempt to return all common receive buffers while the common
buffer pool is being used.

140

Attempt to raise the common pool buffer quota to a value higher than
376 octal.

142-276 Reserved
300

Procedural
Error

Buffer too small - This response ~nforms the user program that the assigned
receive buffer is not large enough for the current incoming message. Recovery
from this error condition is detailed in Section 4.6.2.2.

3-24

Table 3-7
Octal
Code
302

Output Codes (Cont)

Category

Information

Procedural
Error

Nonexistent memory - This response is issued to the user program when the
OMVII microcode attempts to access a CPU memory location that does not
respond. The address that caused the error is returned in BSEL4, BSEL5, and
BSEL 7 for this response.
This error is fatal to the station that initiated the memory access causing the
error. That station must be halted and restarted (see Section 4.6.2.1).

NOTE
With the exception of the buffer too small and nonexistent memory errors, the only control response
fields used by the DMV 11 when posting a procedural error are the type code field in BSEL2, and
the output code field in BSEL6. All other fields remain as set by the user program in the command
that originally generated the procedural error.
304

System
Event

Modem disconnected - This response informs the user program that an on-tooff transition of the EIA signal data set ready (OSR) was detected. Such a
transition indicates that the modem is disconnecting from the communications
line.
Since this is a global response, the content of BSEL3 is zero.

306

System
Event

Queue overflow - This response indicates that the free linked list is empty (see
Section 4.6.2.3).
This error typically indicates that for some reason output responses are being
called for faster than the microcode can process them.

NOTE
This is a global fatal error and the DMVII initializes itself after attempting to return all information (response queue only).
Once this response is issued, the user program has three seconds to retrieve the
next pending response from the CSRs. Three seconds are allowed for each
pending response before the internal microdiagnostics clear the CSRs (see
Section 4.3 for restarting).
310

System
Event

Modem carrier loss - This control response code informs the user program
that the EIA signal carrier detect has gone from on to off while the OMVII
was in the process of receiving a message. Since this is a global response, the
content of BSEL3 is always zero.

3-25

7
7

, 6

5
I

, 5

2
I

o
lEI

BSELO

0
1
MODE CMD TYPE CODE
0

~_2BIT

BSEL2
SEL2
BSEL4
SEL4

EVENT/ERROR
COpE
I
I

BSEL6
SEL6

RDO
I

4
lEO

Ral

, 4 , 3 , 2 , 1 , 0

TRIBUTARY ADDRESS

BSEL3

RDI

•

BSEL5

,I
BSEL7
I

"'BUS ADDRESS BITS 16-21
I

18 BIT ADDRESS MODE
"'ONLY APPLICABLE FOR NON-EXISTENT MEMORY
AND BUFFER TO SMALL ERRORS
MK-2510

Figure 3-9

Control-Out Command Format IS-Bit Mode

3.4.3 Information Response
An information response is issued by the DMV11 microcode in reply to a request for information by the
user program. The format for this response is shown in Figure 3-10. The type code for this response is
010 binary as indicated in BSEL2. BSEL3 contains the tributary address and SEL4 contains the information requested by the user program. If the information requested is from a GSS, BSEL3 contains a
zero.
An information response contains a return key code or a TSS or GSS address in BSEL6 bits 0-4. The
return key codes are used in response to control request keys or protocol events and are encoded as
shown in Table 3-S. The TSS address is used in response to a read or read and clear TSS/GSS command in conjunction with bits 5 and 6 of BSEL6.
Information responses to read or read and clear TSS/GSS control commands, use the TSS address
field (bits 0-4 of BSEL6) to indicate the TSS or GSS location read. Bits 5 and 6 indicate whether the
response is to a read or read and clear input command.

3.5 TSS/GSS ACCESS
When a user program accesses a TSS or a GSS through a control command, the DMV11 reads the
designated location and passes the data to the user program by means of an information response.
Reading a TSS or GSS location results in two bytes of data from that location being stored in BSEL4
and BSEL5 of the information response, with the low-order byte in BSEL4, and the high-order byte in
BSEL5. If a TSS is being read, BSEL3 in the information response contains the associated tributary
address. However, data read from a GSS is passed to the user program through an information response
having a zero in BSEL3.
As described in Table 3-5, any TSS or GSS location can be read, and specific locations can be read and
cleared. Along with the TSS/GSS address, BSEL6 in an information response also contains two singlebit fields that indicate a read or a read and clear TSS/GSS. These information response fields are
described in detail below.
TSS/GSS address

This field (BSEL6, bits zero to four) contains the octal address of the
TSS/GSS location from which the data in BSEL4 and BSEL5 is read.

Read TSS/GSS

When set, this bit (BSEL6, bit five) designates that BSEL4 and
BSEL5 contain the data requested by the read TSS/GSS control command.

3-26

When set, this bit (BSEL6, bit six) designates that BSEL4 and BSELS
contain the data request,ed by the read and clear TSS/GSS control
command. In addition to reading, the requested TSS/GSS location, the
DMVII also clears that location.

Read and clear TSS/GSS

NOTE
The TSS/GSS locations accessible for writing,
reading, and reading and clearing, are listed and described in Table 3-5.

6
I

5
I

2
I

,
I

RDI

BSEL7
I

---

READ, READ
CLR TSS
TSS

NOT USED
13

BSEL2
SEL2

BSEL4
SEL4

DATA

. .

0
o ' 1
CMD TYPE CODE
I

DATA

BSEL5

BSELO

o
lEI

RDO

4
lEO

Ral

TRIBUTAR\, ADDRESS

BSEL3

BSEL6
SEL6

'RETURN KEY OR '
,TSS ,,\DDRE~S
I

o
MK·2391

Figure 3-10
Table 3-8
Octal
Code

Information Response Format

Return Keys for Information Response

Name

Description

Return Modem
Status

This code indicates that BSEL4 and BSELS contain the requested modem
status (see Appendix C).

Buffer Return
Complete

This code indicates that the process of returning all buffers is completed.
Buffers are returned to the user program under the following circumstances:
1. The protocol event STRT message received while running occurred.
This causes all private buffers assigned to the tributary designated by
the address in BSEL3 to be returned.
2. The protocol event maintenance message received while running
occurred. This causes all private buffers assigned to the tributary
designated by the address in B SEL3 to be returned.
3.· The user program issued a control command containing the request key
request halt state causing all private buffers assigned to the tributary
designated by the address in BSEL3 to be returned.
4. The user program issued a global control command (BSEL3 = zero)
containing the request key request halt state. This causes all unused
common pool buffers to be returned.
Information responses containing the return key code for buffer return
complete always have zeros in BSEL4 and BSELS.

3-27

CHAPTER 4
PROGRAMMING TECHNIQUES

4.1 INTRODUCTION
Proper design of user programs for operation with DMVl1-based multipoint and point-to-point networks requires that consideration be given to a number of programming topics. This chapter discusses
the following programming topics.
•
•
•
•
•
•

Command discipline and handshaking;
DMVII start-up;
Criteria for determining user-defined parameters;
Error counter access;
Error recovery procedures;
Booting a remote station.

These programming topics deal with interfacing the user program and DMVII microcode by using the
DMVII command/response structure.

4.2 COMMAND/RESPONSE DISCIPLINE AND HANDSHAKING
The command/response interface between a DMVII and the user program is accomplished through
the DMVII CSRs that are addressed through the CPU I/O page.
Since the DMVII runs in a multiprocessing mode with the associated CPU, the passing of commands
and responses through this interface must be highly disciplined to eliminate the possibility of a race
condition (the user program setting bits in the CSRs after the microprocessor has read those bits). This
interface discipline requires that the user program follow two separate procedures; one for issuing commands, and one for retrieving responses.
Figure 4-1 illustrates the control bits involved in CSR interface discipline. These bits are located in the
DMVII CSRs BSELO and BSEL2. Examination of Figure 4-1 shows that BSELO contains two control
bits named interrupt enable in (lEI) and interrupt enable out (lEO), bits zero and four respectively.
These bits when set, serve to enable the microprocessor to interrupt the main CPU under two circumstances:
1.

When the CSRs become available for the issuing of a command after access is requested by
the user program for that purpose (lEI and RDI).

When the microcode has a response to be retrieved from the CSRs by the user program (lEO
and RDO).

NOTE
Interrupt mode must be used, otherwise, receive
overruns and transmit underruns are very probable.

4-1

NOTE
It is recommended that the interrupt enable (lEI
and lEO) bits be set when interfacing with the
CSRs. It is imperative that they be set when
operating at 56 K bl s because the microprocessor
is halted momentarily on every access to the
CSRs.
The procedures described below defining CSR interface discipline are based on operation in the interrupt mode. As a consequence, the lEI and lEO bits should be set by the user program prior to using the
CSR interface.
7

ROI

lEO

ROO

ROI

o
lEI

BSELO
BSEL2
MK-2390

Figure 4-1

4.2.1

CSR Interface Control Bits

Command Discipline

At start-up time, before the user program can execute any command, it must initialize the DMV11.
This is accomplished by the program setting the master clear bit in BSELI and waiting for the DMVII
to set the run bit.
Once the DMVII is initialized, commands may be issued. All commands are issued by the user program in two successive steps. The first step requests the use of the data port. The second step identifies
the command type and the data port information for the appropriate command, and notifies the
DMVII that the command is in the CSRs. The specific content of each data port is further defined
under each command description in Section 3.3. The handshaking procedure for input commands is as
follows (see Figure 4-2).
•

The user program requests the use of the data port to issue a command by setting request in
(RQI) bit 7 of BSELO. The user should also set bit 0 of BSELO, interrupt enable in (lEI), at
the same time (using the same instruction) to allow the DMVII to interrupt the CPU when
the data port is available. An interrupt -is generated to XXO when RDI is asserted by the
DMVll.

NOTE
The 22-bit mode is used when the software supports
22-address bit buffers. A "one" in bit 3 of BSEL2
indicates to the DMVll that the software supports
the change in the command format required to support 22-address bits.
•

When the data port is available, the DMVII informs the user by setting ready in (bit 4 of
BSEL2) and generating an interrupt to vector XXO.

•

On detecting RDI bit set, the user can: 1) load the appropriate information into SEL4 and
SEL6, and 2) load the input command code into bit 0-2 of BSEL2.

•

If a single command is to be issued, the user program clears RQI. If a series of commands
are to be issued, RQ I can remain set until just prior to the loading of the last command into
the CSRs. By leaving RQI set while issuing a series of commands, the user program is assured of having access to the CSRs after the next response.

4-2

4.2.2 Retrieving Responses
The OMV 11 issues resppnses in two steps. If ROI is not set, the data pertinent to the responses being
issued is loaded into BSEL3, SEL4, and SEL6. Once this is complete, the OMVII sets the ready out
(ROO) bit and the command code in BSEL2. An interrupt through vector XX4 is generated if the lEO
bit is set. Generally, processing an output response involves the following steps:
•

The user program checks for ROO set. This is done by waiting for an interrupt.

•

To use the output interrupt capability, the user program must set the output interrupt enable
bit in BSELO immediately after it detects that the run bit has been set following master
clear.

•

When an ROO set condition is detected, the user program should move the contents of
SEL2, SEL4, and SEL6 into a working storage area and clear ROO in BSEL2 as soon as
possible. When ROO is cleared, the data port (SEL4 and SEL6) is released to the DMVII
for more input or output processing.

4.2.3 'CSR Interface Interactions
User-program access to the CSRs is under complete control of the OMVII microcode. Access to the
CSRs is granted upon request when the user program has a command to issue, or when the microcode·
has a response for the user program. Figure 4-2 illustrates the nature of the access window available to
the user program under interrupt control, when issuing a command, or retrieving a response. As previously indicated, the user program requests use of the CSRs for the purpose of issuing a command by
setting RQI. The OMVl1 microcode makes the CSRs available for the issuing of a command, only
when it is not using them, by setting ROI and interrupting the user program through the floating vector
XXO. As a result, the time period between the setting of RQI by the user program and the granting of
the CSRs through an interrupt is indeterminate.
When commands are being issued from a queue, and the last command has been issued with the user
program still having ownership of the CSRs (ROI is set), there is a mechanism for returning the CSRs
to the OMVII. In such cases, the user program can issue a control command with the code for no
request in the request key field, thereby, signalling the microcode to ignore the contents of the CSRs.
In this way, the possible reading of erroneous data by the DMVII microcode is avoided.
If the user program is to issue a single command, RQI should be cleared prior to issuing the command
to the CSRs, as indicated in Figure 4-2. However, if a series of commands are to be issued, the user
program can leave RQI set. In this circumstance, when a command is issued and ROI is cleared, the
microcode relinquishes the CSRs to the user program as soon as they become available. The time period between clearing RDO upon completing one command, and an interrupt initiating the next command, is also indeterminate.

When the OMVII has a response to be passed to the user program, it sets ROO then interrupts the
main CPU through the floating vector XX4. At this point, the user program has ownership of the CSRs
and can proceed by reading the response. Once the response is read from the CSRs, the user program
should immediately clear the ROO bit. User-program routines responsible for issuing commands and
retrieving responses should limit the CSR access time required to load a command or retrieve a response.
4.3 DMVll START-UP
Starting a OMVII requires that the user program perform a series of steps to; I) configure the OMVII
to operate within the context of the associated network, 2) establish user-defined parameters, and 3)
initiate protocol operations at the DMVII.

4-3

USER

USER CLEARS RQI
NO FURTHER COMMANDS
, TO ISSUE

SETS
RQI
_

* DMV11
* USER CLEARS RDI TO
, , - - - - - - - - - - - - - - - , NOTIFY DMV11 THAT COMMAND
SETS
RDI
USER HAS TOTAL CONTROL OF CSRs HAS BEEN ISSUED
--------~ TO ISSUE COMMAND
(lEI)

*DMV11
SETS
ROO
(lEO)

* USER CLEARS ROO TO

r----------------......
NOTIFY DMV11 THAT
USER HAS TOTAL CONTROL OF CSRs
RESPONSE HAS BEEN RETRI EVED
TO RETRIEVE RESPONSE

* DMV11 HAS OWNERSHIP OF CSRs
MK-2514

Figure 4-2

CSR Access Window

4.3.1 Configuration Procedure
The sequence to configure a DMVII control and tributary station for network operation is formed by
the following steps:
1.

Set the master clear bit and wait for the run bit to set. (See Section 3.3.1).

When the run bit is set, read BSEL4 and BSEL6.

If the contents of BSEL4 equals octal 33, and the contents of BSEL6 equals octal 305, the
start-up diagnostics have successfully executed and the DMVII is running. Any other value
in BSEL6 indicates that an error condition was detected by the start-up diagnostics. The values and meanings of these diagnostic error codes are listed in Table 4-1.

If the DMVII operational mode is software selectable, set the mode for that device by issuing the appropriate mode definition command (see Section 3.3.2). If the mode for the
DMVII is selected by internal switches, this step can be ignored.

4.3.2 Specifying User-Defined Parameters
After a DMVl1 is configured, the user parameters are specified. User-defined parameters include parameters used by the polling algorithm, and parameters specific to protocol operation. In addition,
those user parameters that are specific to the operation of tributaries, are stored in the tributary status
slot (TSS) associated with each tributary. Parameters that are pertinent to overall system operation are
stored in the global status slot (GSS) for the control or tributary station.

4-4

Table 4-1

Diagnostic Error Codes

BSEL6

BSEL4

Description

101

N/A

Branch test has failed and the microcode is spinning in a loop.

102

N/A

6502 internal resister test has failed and the microcode is spinning in a loop.

103

N/A

Load and store instructions test has failed and the microcode is spinning in a
loop.

104

N/A

Compare instructions test has failed and the microcode is spinning in a loop.

105

N/A

Increment and decrement instructions test has failed and the microcode is
spinning in a loop.

106

N/A

Shift and rotate instructions test has failed and the microcode is spinning in
a loop.

107

N/A

Logic instructions test has failed and the microcode is spinning in a loop.

110

N/A

Add with carry, subtract with carry, set and clear decimal mode instructions test has failed and the microcode is spinning in a loop.

111

N/A

Stack push and pull instructions test has failed and the microcode is spinning in a loop.

112

N/A

Subroutine instructions test has failed and the microcode is spinning in a
loop.

113

N/A

Ram scratchpad, CSR, and NPR address resisters addressing test has failed
and the microcode is spinning in a loop.

114

N/A

Ram scratchpad, CSR, and NPR address resisters data test has failed and
the microcode is spinning in a loop.

115

N/A

True interrupt test has failed and the microcode is spinning in a loop.

116

N/A

Ram data and addressing test has failed and the microcode is spinning in a
loop.

117

N/A

Ram alternating data test has failed and the microcode is spinning in a loop.

120

N/A

Indexed indirect addressing mode instruction test has failed and the microcode is spinning in a loop.

121

N/A

Line unit message test has failed and the microcode is spinning in a loop.

305

The microdiagnostics have completed without errors.

4-5

As described in Section 3.3.3, user parameters are specified through control commands configured to
address a TSS or a ass. These control commands write the data contained in BSEL4 and BSEL5 into
the locations specified by bits 0-4 of BSEL6 (TSS or ass address). In establishing polling and protocol
parameters, the user program has the option of accepting the default for a parameter or setting the
parameter to some predetermined value. Chapter 5 details the criteria to be used in determining opti.;
mum values for the various polling parameters. Criteria for determining the remaining parameters,
which generally concern the operation of the communications link, are presented in Section 4.6.

NOTE
Although the majority of user-defined parameters
are 16-bits in length, some are single byte parameters. If the user program wishes to change one of the
single-byte parameters and accept the default for the
other, both parameters must be written. This is necessary because both TSS and GSS user-defined parameters are written on 2-byte boundaries.
The process of establishing user-defined parameters is presented as two separate steps:

Specifying user-defined parameters for control and tributary station TSS structures.

Specifying user-defined pa-rameters for control and tributary station ass structures.

4.3.2.1 Specifying TSS Parameters - TSS parameters that can be specified by the user program are
lIsted in Table 4-2 by name, BSEL3 address, size, and default value. A functional summary of each
parameter is also given. The actual order of setting TSS parameters through appropriately configured
control commands is arbitrary. The complete command series to specify these parameters for TSS
structures at a multipoint control station is listed below:
1.

Issue a series of control commands to set the value for the transmit delay timer. This is referred to as the preset value.

Issue a series of control commands to establish the polling parameters Q and R for the three
polling levels.

Issue a series of control commands to specify values for the active, inactive, unresponsive,
and dead polling state-change parameters.

Issue a series of control commands to specify values for the maximum transmitted message
count.

Issue a series of control commands to set the selection timers for tributaries (or issue a single
command to set the point-to-point station reply timer).

Issue a series of control commands to set the babbling tributary timers.

4-6

Table 4-2

User-Defined TSS Parameters

Name

TSS Addr
(Octal)
BSEL6

Size
(Bits)

Default
(Octal)

XDT
PRESET

230

Q (Active)
Q (Inactive)
Q (Unresp)

231
232
233

8
8
8

377
0
0

R (Active)
R (Inactive)
R (Unresp)

231
232
233

8
8
8

0
100
20

Description
Preset value for
the transmit delay
timer. This parameter provides a
fixed delay between
transmission of data
and maintenance
messages. The default value of 0 =
no delay.

The initial value of
polling urgency (U)
for the tributary:
The TSS for a tributary must be assigned a Q value for
each of the three
activity levels;
active, inactive,
and unresponsive.
This parameter is
applicable only to
TSS structures at
the control station.
The rate (R) by
which the urgency
(U) is increased for
the tributary.
The TSS for the tributary must be
assigned an R value
for each of the
three activity
levels; active, inactive, and unresponsive. Both the
Q and R for a given
tributary are established through a
single control command. Therefore, if

4-7

Table 4-2

Name

TSS Addr
(Octal)
BSEL6

User-Defined TSS Parameters (Cont)

Default
(Octal)

Size
(Bits)

Description
one parameter is to
be set to a unique
value, and the default is to be accepted for the
other, both the default value and the
unique value must be
written. This parameter is applicable
only to the TSS
structures at the
mul tipoint control
station.

NDM-INACT

234

Number of no data
messages required to
go inactive: This is
the number of consecutive polls to be
made (without receiving a data message) before changing the activity
level of that tributary from active to
inactive. This parameter is applicable
only to the TSS
structures at the
control station.

TO-UNRSP

234

Number of timeouts
to go unresponsive:
The number of consecu ti ve polls of a
tributary (without
response) before
changing the activity level of that
tributary from active or inactive to
unresponsive. Both
the NDM-INACT and
TO-UNRSP counts are
established through
a single control

4-8

Table 4-2

Name

TSS Addr
(Octal)
BSEL6

User-Defined TSS Parameters (Cont)

Size
(Bits)

Default
(Octal)

Description
command. Therefore,
if one parameter is
to be set to a
unique value, and
the default is to be
accepted for the
other, both the default value and the
unique value must be
written. This parameter is applicable
only to the TSS
structures at the
multipoint control
station.

TO-DEAD

235

Number of timeouts
to go dead: The number of consecutive
polls of an unresponsive tributary
(consecutive selection timeouts) before the activity
level of that tributary is changed from
unresponsive to
dead. This parameter is applicable
only to the TSS
structures at the
multipoint control
station.

MXMC

235

Maximum transmitted
message count: This
parameter is a count
of the maximum number of abutting data
messages to be
transmi tted by a
station before it
deselects itself.
This count applies
to the TSS structures at both control and tributary

4-9

Table 4-2

Name

TSS Addr
(Octal)
BSEL6

User-Defined TSS Parameters (Cont)

Size
(Bits)

Default
(Octal)

stations in multipoint networks as
well as point-topoint stations. Both
TO-DEAD and MXMC
for a given tributary are established
through a single
control command.
Therefore, if one
parameter is to be
set to a unique
value, and the default is to be accepted for the
other, both the
default value and
the unique value
must be written. At
tributary and pointto-point stations,
the polling parameter TO-DEAD is ignored.

SEL
TIMER

236

Description.

3 (seconds)
(5670 Octal)

4-10

Selection interval
timer: This timer
is started when a
message is transmitted with the
select flag set, and
halted when a valid
reply is received or
the line is resynchronized. The selection timer is used
as a reply timer for
full-duplex pointto-point networks
(see Section 4.4.1).
I t is used as the
select timer at multipoint control stations, and in halfduplex point-topoint networks. This

Table 4-2

Name

TSS Addr
(Octal)
BSEL6

User-Defined TSS Parameters (Cont)

Size
(Bits)

Default
(Octal)

Description
counter counts in
milliseconds (ms)
from 1 to 65,535 ms.

BAB
TIMER

237

6 (seconds)
(13560 Octal)

Babbling tributary
timer: This timer
is used to detect
a babbling tributary (see Section
4.4.2). In a
multipoint network
this parameter is
applicable only to
the control station.
However, this parameter is applicable
to both stations in
point-to-point networks operating
half-duplex.

4.3.2.2 Specifying GSS Parameters - As previously indicated, when one or more tributary addresses
are established at a DMVll, the DMVII 's microcode automatically creates a GSS for that control or
tributary station. The GSS parameters that can be specified by a user program are listed in Table 4-3
by name, BSEL3 address, size, and default value. A functional summary of each parameter is also
given. If a value is not specified for a parameter the microcode uses the default value. Specifying a
user-defined GSS parameter requires that BSEL3 in the pertinent control command contain zero. The
control commands necessary to specify GSS parameters for a multidrop station are listed below:
1.

A control command to specify the number of sync-characters (NUM SYNC) that are to precede nonabutting transmit messages.

A control command to set the streaming tributary timer.

Three control commands to establish values for the global polling parameters delta time
(DELTA T), dead tributary (DEAD T), and poll delay, respectively.

Specific user-defined TSS and GSS parameters are common to both control and tributary stations.
Note that control commands specifying TSS paraPleters must have the address of the tributary associated with the TSS being accessed in BSEL3. Similarly, each control command specifying a GSS parameter must have BSEL3 set to zero. Since the prior steps have covered user-defined TSS and GSS

4-11

parameters (see Table 4-2 and 4-3) at the control station, the two steps listed below complete the parameter-specifying process at the tributary stations:
1.

Issue a series of control commands at each tributary station to set the 'maximum transmitted
message count (MXMC) for each active TSS in a tributary station TSS structure. Note that
, the 8-bit value for MXMC must be placed in BSEL5 of each command (the tributary station
microcode ignores BSEL4 in these commands). The procedure for determining an optimum
value of this parameter for tributary stations is the same one used for control stations.

Issue a single control command at each tributary station to set a value for the number of
sync-characters (NUM SYNC) that are to precede nonabutted transmit messages. The procedure for determining an optimum value of this parameter for tributary stations is the same
one used for control stations.
Table 4-3

User-Defined GSS Parameters

Name

GSS Addr
(Octal)
BSEL6

Size
(Bits)

Default
(Octal)

NUMSYNC

233

10 (low
speed)
15 (high
speed)

Number of sync-characters:
This global value specifies the number of synccharacters that are to
precede nonabutting transmitted messages. This
parameter applies to all
stations. Low speed is
defined as less than 56K
bls, and high speed is 56K
b/s.

STREAM
TRIB

234

6 (sec.)
(13560
Octal)

Streaming tributary timer
preset: This timer is used
to detect a streaming tributary (see Section 4.4.3)
and Table 3-7). In a multipoint network, this
parameter is applicable
only to the control station. However, in pointto-point networks, this
parameter is applicable to
both stations.

DELTAT

235

200 (ms)
(310
Octal)

Delta time: This is the
polling algorithm u pda te
increment. This global
parameter, which, is applicable only to multipoint control stations,
is used by the polling

4-12

Description

Table 4-3

Name

GSS Addr
(Octal)
BSEL6

User-Defined GSS Parameters (Cont)
Size
(Bits)

Default
(Octal)

Description
algorithm to calculate
polling urgency (see
Section 5.2.1). The default value of 200 ms is
the minimum value for this
parameter. DELTA T is also
used as the interval for
updating the transmit
delay timer.

DEADT

236

10 (sec.)
(17500
Octal)

Dead timer: This is the
interval between polls for
dead tributaries. This
global parameter applies
only to multipoint control
stations.

POLL
DELAY

237

o (no

This parameter provides
for a fixed delay between
polls for all tributaries
in a network. If the default is accepted, the
next poll for any tributary occurs immediately
following the current
poll.

delay)

4.3.3 Protocol Operation
At this point the DMVII has been configured for operation in the associated network and is ready for
protocol operation. The steps required to initiate protocol operation are:
1.

Place established tributaries in the ISTRT state by issuing one control command containing
the request key. Request ISTRT state for each tributary address.

If the DMVII is a station in a point-to-point network, one control command must be issued
containing the request ISTRT state request key with a tributary address of one in BSEL3.

The DMVl1 confirms that the protocol is operational at each tributary by issuing a control
response (one for each control command issued) containing the protocol event code for
DDCMP run state entered.

4.4 CRITERIA FOR DETERMINING COMMUNICATIONS LINK PARAMETERS
User-defined TSS and ass parameters fall into two categories: polling parameters that provide for
user-program control over the dynamic activity of the polling algorithm, and communications link pa-

4-13

rameters that provide the user program with the ability to regulate data traffic over the physical communications line. Referring to Tables 4-2 and 4-3, the communications link parameters include:
•
•
•
•
•
•

Selection interval timer,
Number of sync-characters,
Babbling tributary timer,
Maximum transmitted message count,
Streaming tributary timer,
Transmit delay timer.

Values for the selection interval timer and the number of sync-characters are interrelated, as are values
for the babbling tributary timer and the maximum transmitted message count. These interrelated parameters are described in Sections 4.4.1 and 4.4.2.

4.4.1 Setting the Selection Interval Timer
The function performed by the selection interval timer at a DMVII depends on the mode selected for
that DMV II. In full-duplex point-to-point networks, this timer is used as a reply timer for the purpose
of message accountability. This timer serves as a selection interval timer when the mode for the associated DMVII is one of the following:
•
•
•

A full-duplex control station;
A half-duplex control station;
A half-duplex point-to-point station.

In this capacity, it performs the link management function and provides for message accountability.
Link management is the process of controlling the transmission and reception of data over networks
where there are two or more transmitter/receiver devices actively connected to the same physical communications link. This applies to half- and full-duplex multipoint networks as well as half-duplex pointto-point links. On half-duplex links, only one transmitter can be active at any time, and on full-duplex
links, only one slave transmitter can be active at a time.
A station on such links can transmit when it is selected or granted ownership of the link. Link ownership
is passed through use of the select flag in the DDCMP message header. Detecting a select flag in a
received message allows the receiving station to transmit after message reception is completed. Sending
a select flag means that the transmitting station ceases transmitting after the current message is sent.
A selection timer detects the loss of a select flag by timing the interval required to receive the longest
message from a station. A timer is started when a station is selected and reset when valid messages are
received from that station. When the timer interval is exceeded at the sending station (a message was
not received during the period of the timer) it is assumed that messages with the select flag were either
transmitted or received in error.
At this point, the station that originally sent the messages with the select flag set assumes ownership of
the link. This station resumes transmitting as if it had received a valid select return.
The values assigned to select interval timers at stations in half-duplex point-to-point networks should be
different at both stations to avoid possible deadlock race conditions. For both multipoint control stations
and half-duplex point-to-point stations, the criteria for determining the value for a select timer includes
such factors as:
•
•
•
•
•

Maximum message length;
Number of sync-characters;
Line speed;
Line turnaround time;
Message processing delays.

4-14

As indicated in Table 4-3, the ass parameter number of sync-characters has two defaults; one for lowspeed operation (10), and one for high-speed operation (15). The operational speed range of a DMVll
is specified by the line unit low-speed/high-speed switch which is placed in the appropriate position
when the DMVll is hardware configured (see Section 2.5). In the low-speed position the DMVll can
operate at line speeds up to 19.2K bls, and in the high-speed position the device line speed is 56K b/s.
It is recommended that the default for the appropriate line speed range be taken for this parameter.
Some recommended values for a selection interval timer are given in Table 4-4. The calculations shown
in Table 4-4 include the following overhead factors:
256 bytes of data
28 bytes of header, sync, and pad characters
Total

284 bytes

The formula used to derive the values listed in Table 4-4 is:
8 bits per byte
X

284 bytes per message + RTS/CTS delay = Timer value (in seconds)

baud rate (bits
per second)

NOTE
Most modems include an RTS/CTS delay that must
be included in the calculation of the value for the selection intenal timer. When operating with an external (EIA) modem, the typical delay used is 150 ms.
The delay used when operating with the integral
modem is 100 p,s.
Table 4-4

Recommended Selection Intenal Timer Values

Bits Per Second

Calculated Timer Value for a 256 Byte Message

4.8K

473 ms + 150 ms = 623 ms (700 ms)

9.6K

236 ms + 150 ms = 386 ms (400 ms)

56K

40.5 ms + 0.1 ms = 40.6 ms (50 ms)

The values listed in Table 4-4 represent absolute minimums. In most cases, specific applications require
additional delay time over these values to prevent a timeout during reception of a valid message. Requirement for additional delay time can be caused by processing delays that occur when receiving from
a non-DMVl1 device, or by line delays encountered when dealing with satellite networks. When determining this value, keep in mind that it represents the time the system can reasonably expend waiting for
a response from another station.
When used as a reply timer, the selection interval timer sets the maximum waiting period between sending a message and receiving an acknowledgement before taking error recovery actions. This timeout is
necessary to recover from outages and the distortion of messages by the link. This timeout also prevents
the protocol from being deadlocked.

4-15

The same criteria used to determine a value for a selection interval timer in multipoint networks, are
also. used to determine a value when this timer is used as a reply timer. As shown in Table 4-2, the
default value for both cases is three seconds.
4.4.2 Setting the Babbling Tributary Timer
This user parameter is applicable to half-duplex and full-duplex multidrop network control stations. A
babbling tributary is a tributary that continues to transmit valid DDCMP messages after a programmable timeout has expired, thereby, denying equal access to other nodes. This situation is controlled by
the babbling tributary timer which monitors the total time period a tributary continuously transmits
without relinquishing the communications line. When this period exceeds the timeout period of the
babbling tributary timer, the user program is notified through a control response. The control response
contains the code for a babbling tributary along with the identity of the offending tributary. When a
babbling tributary is detected, the control station takes no action beyond this notification.
A major consideration in determining a value for the tributary timer is the total time interval that a
given tributary requires to end a selection interval. Determining the value for this timer is similar to
that for the selection interval timer because the same range of factors are used as criteria for calculating the value. The main difference in the two determinations is that the total number of message
bytes should be used in babbling tributary timer parameter calculations rather than the number of
bytes in the longest message.
A value for the maximum transmitted message count parameter must also be considered in conjunction
with the parameter for the babbling tributary timer. The user-defined parameter to. set this counter
places a limit on the number of messages that a tributary can transmit during the selection period. This
is done by forcing the select flag when the count of messages received from a tributary equals the value
of the maximum transmitted message count. This count relieves the user program from having to limit
the number of messages queued for transmission in order to avoid a babbling tributary condition.
In any case, the period established for the timeout of a babbling tributary timer should be long enough
to ensure that timer expiration definitely indicates an error condition. In addition, the parameter assigned to the maximum transmitted message count should also be considered when establishing the period of the babbling tributary counter.
4.4.3 Setting the Streaming Tributary Timer
A streaming tributary is a tributary station on a multipoint line (or an associated point-to-point station)
that continues to assert the carrier signal on the link after it has relinquished ownership of the link. In
normal operation, ownership of the link is returned to the control station when it receives a select flag or
the period of the selection interval timer is exceeded. A timeout of the ·streaming tributary timer indicates a potential jamming of the link by a defective tributary station, a defective point-to-point station, or a malfunctioning modem.
The streaming tributary is started when ownership of the link is granted to the control station by the
remote station, and stopped when the carrier is dropped by that station. When a streaming tributary is
detected, through expiration of the streaming tributary timer, the user program is notified in the same
manner as with a babbling tributary. The control station does not transmit until the carrier is dropped. I
Determination of a value for the streaming tributary timer requires consideration. of such factors as
settling time of the communications line and modem delays. As with determining periods for the selection interval timer· and the babbling tributary timer, the period specified for this timer should be long
enough to preclude premature expiration of the timer. For most network applications the default of one
second is sufficient.

4-16

4.5 ERROR COUNTER ACCESS
The DMVII is equipped with a large compliment of error counters designed to isolate a wide range of
error conditions. The TSS for each established tributary contains seven error counters along with three
statistical counters that provide background information for error analysis. In addition, the GSS at each
station contains four error counters that tabulate errors that are global to the station. The three TSS
statistical counters are 16 bits in length, and the threshold error counters are three bits in length. The
remaining TSS/GSS error counters are eight bits long.
4.5.1 Reading the Counters
Both TSS and GSS counters are accessed through an appropriate control command with the content of
the requested counter or counters being returned through an information response (see Sections 3.3 and
3.4). Through the control command, the user program has the option of reading, or reading and clearing
the counters. When doing error analysis it is recommended that a user program read and clear these
counters to assure a zero-base for subsequent sampling of the counters. If copies of the counters are
being maintained in main CPU memory, it is also recommended that counters be read and cleared.
NOTE
The three-bit threshold error counters are automatically reset when the maximum count is reached so
that access to these counters is restricted to reading
only.
The DMVII error and statistical counter structure is designed to be complimentary. As an example of
this complimentary structure, consider the data errors inbound counter and the d~ta messages received
counter. The data errors inbound counter tabulates the errors related to the validity of message reception such as block-check errors, whereas, the data messages received counter records the total number
of messages received. A ratio of message reception errors to total number of messages received can be
derived from these two counters.
4.5.2 Counter Skew
When performing error analysis, there is a potential of skew between counts due to read time lags and
the requirement that counters be read one at a time. The probability of skew between counts is a function of line speed; the higher the line speed, the greater the probability of a skew condition. An example
of this potential skewing is the possible discrepancy between the number of selection intervals and the
number of selection timeouts. A skew could result from additional selection timeouts occurring while
the counters are being read.
If circumstances require that error/statistical counters be read without the potential for skew, this can
be done by halting the protocol at the tributary. With the protocol halted, the contents of the error/statistical counters in a TSS and in the GSS are frozen at the counts recorded when the protocol
was halted. The counters can then be read without the problem of skew due to read time lags.

4.6 ERROR RECOVERY PROCEDURES
Within a DMVl1-based network, there are three basic levels of error recovery involving the user program:
1.

Procedural violations where only the user program is notified.

Recovery from errors requiring protocol shutdown initiated by the user program.

Fatal errors resulting in system shutdown with minimal notice to the user program.

Referring to Table 3-7, procedural error codes from 100 to 140 are reported to the user program with
no recovery required. The remaining two procedural errors (codes 300 and 302) involve error recovery
levels two and three respectively. All network errors require recovery through protocol shutdown, and
the control response (queue overflow) could result in network shutdown.

4-17

4.6.1 Recovery from Network Errors
In all cases, recovery from network errors requires that the protocol be halted at the tributary or station
recording the error. Two similar but separate procedures are recommended for recovery from threshold
errors, and babbling and streaming tributary errors. These recovery procedures are described below.
4.6.1.1 Recovery from Threshold Errors - DMVl1 threshold errors are detailed in Section 5.3.3. The
recommended recovery procedure to be initiated by the user program at the station recording the errors
is presented below:
1.

Halt the protocol (see Table 3-6).

Read the error counters to determine the nature and cause of the threshold error condition. If
the error results from a shortage of receive buffers, correct the condition. If the transmit or
selection threshold is being exceeded, check the operational condition of the remote station.

When the conditions causing the errors have been eliminated, restart the protocol (see Section 4.3.3').

4.6.1.2 Recovery from Babbling and Streaming Tributary Errors - Babbling or streaming tributary errors are created when their respective timers are exceeded. Therefore, a timeout can result from an
actual error condition, or because the period of the timer is too short for the type of message activity on
the line (see Sections 4.4.2 and 4.4.3). A suggested recovery procedure to be used when encountering
these conditions is:
1.

Halt the protocol.

Check the value of timer parameters and increase if the value is not appropriate.

Restart the protocol (see Section 4.3.3).

If this error condition persists, reconfigure the station as specified by Section 4.3.1.

When the cause of the timeout originates at the remote station, action must be taken at the
remote station to ascertain and correct the fault. The local station is at fault only if the values
of the timer parameters are inappropriate.

4.6.2 Recovery from Procedural Errors
The three procedural errors that require a recovery procedure are:
L
2.
3.

Nonexistent memory error.
Buffer too small error.
Queue overflow error.

The recovery procedure for each of these errors is detailed in Sections 4.6.2.1 through 4.6.2.3.
4.6.2.1 Recovery from a Nonexistent Memory Error - Nonexistent memory errors occur when the
DMV11 tries to access an allocated receive or transmit buffer having an invalid bus address. When this
error is detected, the DMVII posts a control response to the user program containing the invalid address (see Section 3.4.2). It is up to the user program to determine whether the nonexistent address
concerns a transmit or receive buffer.
NOTE
Depending on microcode processing circumstances,
the nonexistent memory address returned to ,the user
program could have been incremented to the next sequential location.

4-18

The suggested recovery procedure for this error is as follows:
1.

Halt the protocol for the tributary or station recording this error to initiate return of all outstanding buffers.

If the error concerns a buffer from the common pool, the user program should issue the global halt command to initiate return of all outstanding receive buffers from the common pool.

Restart the protocol and reallocate buffers as necessary.

Persistent recurrence of this error indicates a possible main CPU or DMVII malfunction.
NOTE
If the network line speed is 56K bls, the requests for
retransmission generated by a nonexistent memory
address can result in the overflow of the DMVll response queue causing a fatal system error (see Section 4.6.2.3).
4.6.2.2 Recovery from a Receive Buffer Too Small Error - When the DMVII receives a message, it
first checks for the availability of a buffer from the common buffer pool linked list, and if one is available, it uses that buffer. If the common buffer pool is empty or not enabled, the private buffer linked
list is checked. If a private buffer is not available, the receiving station NAKs the incoming message.
The steps taken by the DMVll microcode in this process are listed below.
1.

Is the message number in sequence? Yes, continue; No, ignore message.

Is the common buffer pool enabled? Yes, continue; No, go to Step 6.

Is the common buffer pool quota = O? Yes, go to Step 6; No, continue.

Is a common pool buffer available? Yes, continue; No, go to Step 6.

Is the common pool buffer too small? Yes, go to Step 8; No, use this buffer.

Is a private buffer available? Yes, continue; No, send NAK - buffer temporarily unavailable.

Is private buffer too small? Yes, send NAK - buffer too small; No, use this buffer.

Is private buffer available? Yes go to Step 7; No, send NAK - buffer too small.
NOTE
The DMVll does not scan the common pool or private linked list structures looking for a buffer of sufficient size. Rather, it uses the next available buffer
from the list.

Buffer too small errors apply only to receive buffers. The procedure for recovery from this error is
dependent on whether the allocated buffer is from the common pool or is a private buffer. The applicable recovery procedures are explained below.
A.

Common pool buffer too small
1.

Assign a private buffer of sufficient size to the receiving tributary through a buffer address/character count command (see Section 3.3.4).

4-19

Both private and common pool buffers too small
1.

Halt the protocol for the offending tributary to initiate return of all outstanding private buffers.

Restart the protocol.

Assign a private buffer of sufficient size to the receiving tributary through a buffer address/character count command (see Section 3.3.4).

Private buffer too small, and common pool not enabled
1.

If buffers from the common pool are available to other tributaries, and are of sufficient size,
enable common pool buffers for this tributary (see Section 3.3.4).

If the common buffer pool is not in use for other tributaries, follow recovery procedure B
above.

4.6.2.3 Recovery from a Queue Overflow Error - This error is always fatal to the DMVII recording
the error since it. forces automatic shutdown of the device. The basic cause of this error is the inavailability of link blocks from the free linked list (see Section 5.4.1.1). Typically, this error results
when the internal response queue overflows because the DMVII generated responses faster than the
user program could retrieve responses from the queue. This error can also occur if an inordinate number of receive buffers have been allocated. One cause of response queue overflow is the occurrence of
repetitive nonexistent memory errors in high-speed networks (see Section 4.6.2.l).
When this error occurs, the DMVII posts the most current entry in the response queue to the user
program. The user program then has three seconds after being interrupted to retrieve the response. If it
is retrieved during this three second window, the next response is posted. As long as the user program
retrieves each response within this window, the process continues until the internal response queue is
empty. These responses can then be analyzed to determine the cause of the queue overflow.
After the last response has been posted, or the three second response period has expired, the DMVII
shuts itself down. At this point, returning the DMVII to operational status requires that the start-up
procedure be initiated from the beginning (see Section 4.3).

4.7 BOOTING A REMOTE STATION
DMV II-based networks provide the user program, at the multipoint control station or point-to-point
station, with the ability to boot the ma:in CPU at a remote station that has been shut down due to power
outage or software malfunction. There are three ways this boot function can be performed:
1.

Remote load detect: The control station starts the primary MOP boot procedure for a remote
station.

Power-on boot: The first poll received after power-up at the remote station causes the
DMVII at that station to request that the control station start the MOP boot procedure.

Invoke primary MOP: The user program at the remote station causes the DMVII to request
that the control station start the primary MOP boot procedure.

4-20

NOTE
Control station is either a multipoint control or
point-to-point station that is transmitting (over the
link) the boot or requested program to the remote
station. Remote station is either a multipoint tributary or point-to-point station that is receiving
(over the link) the boot or requested program.

NOTE
Power-on boot, remote load detect, and invoke
primary MOP are not mutually exclusive. All three
features could be used in a particular application.
Primary MOP boot procedures require that the DMVll be switch-configured in the manner specified
in this section. The steps taking place at the remote station and over the communications line leading to
each of the three primary MOP boot functions are presented in the following sections.
4.7.1 Steps Leading to a Remote Load Detect Boot
The steps taking place at the DMVll remote station and its host CPU in response to an enter MOP
mode message from the control station are:
1.

The DMVll NPRs a tight-loop routine into main memory.

The DMVll transfers control to the routine through the power fail/restart vector. This routine inactivates the CPU to prevent any intervention during the :NPR process.

The DMVll then sends a primary MOP request program message to the control station. The
control station responds in turn with a primary MOP memory load with transfer address message containing the boot or related program to be loaded into main memory at the remote
station.

The DMVll NPRs that program into main memory, then starts executing the program.

At this point the remote station is operating in the manner intended by the down-line loaded
program.

The steps occurring over the communications line during a remote load detect boot are:
1.

The control station sends an enter MOP mode message to a remote station.

The remote station recognizes the address and password in the message, then inactivates its
host CPU.

The remote station then responds with a primary MOP request program message.

The control station responds to this message with a primary MOP memory load with transfer
address message containing the boot or related program to be loaded into the host CPU at the
remote station.

4.7.2 Steps Leading to a Power-On Boot
When power is restored after a shutdown at a remote station, the DMV 11 performs the same steps used
during a remote load detect boot. However, the first two steps performed over the communications line
are omitted, and the tributary station responds to the first poll from the control station with an MOP
request program message. The same sequence used in the remote load detect boot procedure 'is then
followed.
4-21

4.7.3 Steps Leading to an Invoke Primary MOP Boot
This boot operation is initiated when a user at a remote station sets the boot and master clear bits in the
DMVll initialization register (see Section 3.3.1). The steps taken by the DMVll are the same as with
a power-on boot.
4.7.4 DMVll Switch Settings for the Boot Functions
At remote stations, in networks supporting the primary MOP boot functions, the switches must be configured in a specific way in order to properly perform the boot functions (see Section 2.5 and Table 26). .
NOTE
The switch setting procedures described below apply
only to tributary stations in a multipoint network
and one node in a point-to-point network.
The unit number (zero or one) of each DMVl1 must be appropriately set. This number allows the boot
program, once it is loaded into the host CPU, to identify the specific DMVll (within the host's floating
address space) performing the boot.
NOTE
When primary MOP booting is supported in a network, the operating mode of each tributary station
eligible for booting must be set in the switches rather
than through the mode definition command.
The operating mode of a DMVll is specified by setting the mode enable switch to one (OFF) (switch
number 1 of the boot enable switch pack), and setting switches numbered 6, 7, and 8 to the required
operating mode. The settings for these switches are listed in Table 4-5.
4.7.4.1 Switch Settings for the Power-On Boot Function - To enable the power-on boot function at a
remote station, switch number 4 of the boot enable switch pack (power-on boot) must be set to one
(OFF). In addition, the tributary address of this station must be set in the DDCMP address switch
pack.
4.7.4.2 Switch Settings for the Invoke Primary MOP Boot Function - The DMVll switch settings for
the invoke primary MOP boot function are the same as those for the power-on boot function. However,
the setting of the power-on boot switch has no affect on the invoke primary MOP boot.
An additional feature of the invoke primary MOP boot is that it may allow the tributary address of the
remote station to be software assigned instead of switch assigned. This feature is only valid for remote
stations that are multipoint tributaries. To use this feature, the following conditions must exist.
•

The tributary address/password in the DDCMP address switch pack must be zero.

•

The user program at the remote station must have established the tributary using the control
command (establish tributary). If the remote station is using the multiple address tributary
option, the tributary address used for booting must be the first one established.
NOTE
Invoke primary MOP boot with the software-assigned tributary address does not work if the poweron boot switch is enabled.

4-22

Table 4-5
Mode
Switches

Mode Switch Settings

Line
Characteristics

Network
Configuration

DMCll Line
Compatibility

Half-duplex

Point-to-point

Yes

OFF ON

Full-duplex

Point-to-point

Yes

OFF ON

Half-duplex

Point-to-point

OFF OFF ON

Full-duplex

Point-to-point

OFF

Half-duplex

Multipoint control
station

N/A

OFF ON

OFF

Full-duplex

Multipoint control
station

N/A

OFF OFF

Half-duplex

Multipoint tributary
station

N/A

OFF OFF OFF

Full-duplex

Multipoint tributary
station

N/A

4.7.4.3 Switch Settings for the Remote Load Detect Boot Function - To enable the remote load detect
boot function at a remote tributary station, switch number 5 of the boot enable switch pack (enable
remote load detect) must be set to one (OFF). For the remote load detect boot function, the switchspecified tributary address also serves as the password which is contained in the enter MOP mode message.
When using boot functions in point-to-point networks, the tributary address/password switches can, for
security purposes, be set to a unique value since the address of a point-to-point node is always known to
be one.

4.8 MAINTENANCE REGISTER EMULATION
The DMV 11 is placed into maintenance mode when the user program sets bits and 6 at the same time
in BSEL 1. When this happens, the microcode enters a maintenance loop and sets MNT RDY (bit 7 of
BSEL2) to indicate that the microcode is ready to receive a command as defined by bits zero through
three of BSEL2 (see Figure 4-3). The functions of these commands are described in Table 4-6.
NOTE
The microdiagnostics must complete tests 1-12 as a
minimum before allowing entry into the maintenance
loop.
In the maintenance mode, the functions of the CSRs are redefined as follows:
•

BSELO, bits zero and four, enable the respective microprocessor LSI bus interrupts as defined by bits one and two. See Figure 4-3.

4-23

•

BSEL2, bits zero through three, define the maintenance loop command function. Bits four
and five are used for interrupting the CPU if an internal microprocessor interrupt occurs.
These interrupts are enabled by BSELO. Bit seven is set by the microprocessor when the
maintenance loop is ready to receive another command function in bits zero through three
(Table 4-6).

•

SEL4 contains a DMVII memory location for function codes one through five (Table 4-6).

•

SEL6 contains data written or read for functions one, two, and six. It also contains a 16-bit
address for 'functions three and four.

•

SELIO contains the upper address bits for functions three and four. Only the low byte of this
CSR is used.

NOTE
BSELI0 and 11 are only used in 22-bit mode.
BSEL 12 through 17 are not shown because they are
never used by the user/DMVll-command structure.

7
BSEL

I I. I. I I I
.

EN
"B"

III
P IlL P, EN
INTA INTB "A"

BSELO

"B"
INT

FUNCTION CODE

BSEL2
SEL2

DMV11 MEMORY LOCATION (LOW BYTE)
FOR FUNCTIONS 1-5

BSEL4
SEL4

DATA READ OR WRITIEN FOR FUNCTIONS 1, 2 & 6 or 16 BIT ADDRESS FOR FUNCTIONS 3 & 4

BSEL6
SEL6

RUN

IMNT
REO

MTR
CLR

MNT
ROY

NOT USED

BSEL3
.~

. .

UPPER ADDRESS BITS
FOR FUNCTS 3 & 4

UNUSED
I

NOT USED
I

BSEL11

"A"
INT

DMV11 MEMORY LOCATION (HIGH BYTE)
FOR FUNCTIONS 1-5

BSEL5
BSEL7

SEL10
BSEL10

o
MK·2517

Figure 4-3

DMVII Maintenance Loop Command Format

4-24

Table 4-6

Maintenance Command Functions BSEL2 Bits 0-3

Octal Code
Bits 0-3

Function

Reserved to avoid unpredictable results.

Read DMVII memory location specified by SEL4 (l6-bit address specifying a
byte). SEL6 contains the data read from this location.

Write DMVII memory location specified by SEL4. SEL6 contains the data
written to this location.

Read 256 bytes of DMVII memory. SEL4 points to the starting DMVII memory address from which the information is read. The lower eight bits of this address are ignored. SEL6 and BSEL8 point to the starting LSI-II bus address
where the information is stored.

Write 256 bytes of DMVII memory. SEL4 points to the starting DMVII memory address to which the information is written. The lower eight bits of this address are ignored. SEL6 and BSEL8 point to the starting LSI-II bus address
from which the information is read.

Set the 6502 microprocessor's program counter to the value contained in SEL4.
This is used to start the microprocessor executing code at the DMVII memory
location specified by SEL4.

Set internal loop and null clock for functional diagnostics. Null clock is initialized for 56K b/s.

Set maintenance interrupt flags and clear interrupt disable in processor status.

4-25

CHAPTER 5
ASPECTS OF DMVll
MICROCODE OPERATION

5.1 INTRODUCTION
The functionality of the DMVll results from the microprocessor and its associated microprogram or
microcode. This chapter discusses the microcode as it relates to:
•

The polling algorithm,

•

Error recording, and

•

The internal data base.

5.2 DMV11 POLLING ALGORITHM
In a polling operation the tributaries are in effect asked one by one whether they have anything to
transmit. To accomplish this, the control station sends a polling message with a unique tributary address down the line. The station which recognizes the address responds with data messages or a positive
response.
With DMVlls, polling is based on a priority scheme which is derived automatically and applied dynamically by the microcode. To control polling and data message transmission, the DMVll uses the
following information:
•

The tributary's recent poll history,

•

The tributary's user-defined parameters,

•

The tributary's protocol state.

In regard to protocol state, the multipoint network control station polls all established tributaries that
are not in the DDCMP halt state. The protocol state of every established tributary is maintained in the
associated TSS by the control station. When a tributary is eligible for polling, all outstanding transmit
messages for that tributary are sent as the poll, up to the limit imposed by the maximum transmitted
message count. If no transmit messages are available for a tributary eligible for polling, the DMVll
automatically transmits the appropriate DDCMP control message.

The DMVII polling algorithm determines which tributary is to be polled next, based on each tributary's polling urgency level. The DMVll polling algorithm employs the user-defined TSS and GSS polling parameters as the basis for categorizing tributaries into polling levels. The polling algorithm also
determines the rate at which polling urgency is increased within 'each polling level. A tributary's polling
level is based on its recent response history. This classification mechanism, combined with periodic incrementing of polling urgency., results in the most active tributaries being polled most often.

5-1

5.2.1 Calculating Polling Urgency
The polling urgency (priority) of each tributary is periodically calculated when a global timer expires.
This periodic calculation enables the algorithm to enforce minimum poll intervals for each tributary,
and to account for competition between tributaries. The minimum poll interval prevents unneeded polls
from:
•
•
•

Delaying other tributaries,
Interfering with output traffic, and
Causing unnecessary processor overhead.

The polling urgency of a tributary is calculated as a linear function of time elapsed since the last poll.
The calculation is truncated when the maximum value of 255 is reached. The three parameters in this
calculation are:
1.
2.
3.

Q - the initial value of the polling urgency (U);
R - the rate at which Q is to be increased;
DELTA T - the polling algorithm global update interval.

Figure 5-1 shows the relationship between these three parameters. The appropriate choice of Q and R
can give a variety of behaviors. For this reason, the choice of these values must be based on the desired
performance. One method of choosing Q and R is to define the minimum poll time and the time to
reach maximum poll urgency, and to use these values in the following equations.
Minimum poll time = 128-Q (DELTA T)
R
Time to reach maximum poll urgency = 255-Q (DELTA T)
R
DELTA T is the user-defined period of the global timer and its value depends on the line speed. It must
be smaller than the smallest nonzero minimum poll interval, but no smaller than 200 ms. The poll priority is calculated for each tributary and stored in a single byte of the TSS. With every DELTA T, the
polling urgency byte is updated. The following interpretation is placed on its value. These values are
represented as base lines on the graph of Figure 5-1. Figure 5-2 shows the relationship of the polling
urgency to different values of Q and R.

o - 127

Do not poll the tributary. The minimum poll interval, has not expired.

128

Minimum poll interval has expired. The tributary is eligible for polling.

129 - 254

Minimum poll interval is exceeded. The tributary is eligible for polling. The
higher values indicate increasing priority in the event of competition between
tributaries.

255

Maximum poll urgency is reached. Competition between tributaries at this priority is round-robin.

This method of determining values for Q and R is applicable when static behavior is desired. For many
applications, however, dynamic behavior can improve performance by polling active tributaries at a
faster rate and with a higher priority than inactive tributaries.
During each DELTA T time period, the control station polling algorithm updates the urgency of each
operational tributary by adding the value of R for the appropriate polling state (excluding dead) to the
urgency value of each tributary. This updating sequence is performed on the TSS data base in the order

5-2

in which tributaries were originally established at the control station. When the polling algorithm determines that the next poll is to be sent, it selects the tributary to be polled by scanning the TSS data base
(in the original order of tributary establishment), starting at the TSS following the last tributary polled.
In this process, the tributary having the highest value of U from active, inactive, and unresponsive
tributaries is selected as the next tributary to be polled.
TIME TO
MAXIMUM URGENCY

,-------------------------------~-------------------------------255

------------------------- -----

ELIGIBLE FOR
POLLING

MINIMUM
POLLING INTERVAL

<.!)

a:: 128
::::>

I ~-------------~--------------~

127

<.!)

NOT POLLED

::::i
....J

a!l..

~ t =200ms
MK-2643

Figure 5-1

Interrelationship Between Polling Parameters Q, R, and DELTA T

If an urgency of 255 is detected during the process of scanning the TSS data base for the tributary
having the highest value of U, the scan process is halted and that tributary is immediately selected for
polling. Once the selected tributary is polled, its urgency reverts to the assigned value of Q for its polling level.

Dead tributaries are polled at a rate determined by the user-defined parameter DEAD T. One dead
tributary is polled at each expiration of the DEAD T timer, and the scan of dead tributaries is resumed
from the last dead tributary polled.

5-3

266

127~----------~------------~-----------.----------~------------------

::J

<.::I

Z
::::J

...I

2.0

3.2

4.0

6.375
DELTA

Figure 5-2

8.0
T

9.55
200ms

12.0

16.0
MK·2647

Relationship Between Polling Parameters Q, R, and the Minimum Polling Interval

The dynamic polling algorithm uses Q and R values based on dynamically modified states. There are
four of these states:
1.

Active - The polling algorithm maintains a tributary as active when it responds to polls with
data messages.

Inactive - The polling state of an active tributary is changed to inactive when it responds to a
consecutive number of polls with nondata DDCMP messages. The count of consecutive nondata messages received from a tributary in the active state is designated by the user-defined
parameter NDM-INACT (number of no-data messages required to go inactive).

Unresponsive - A tributary currently active or inactive is changed to the unresponsive state
when it fails to respond in any way to a consecutive number of polls (each poll results in a
selection timeout). The count of consecutive polls without responses is designated by the
user-defined parameter TO-UNRESP (number of timeouts to go unresponsive).

Dead - A currently unresponsive tributary which continues to be unresponsive to consecutive
polls is changed to dead. This occurs when the number of selection interval timeouts designated by the user-defined parameter TO-DEAD (number of timeouts to go dead) is exceeded. Unlike tributaries in the other polling states, dead tributaries are always polled on a
round-robin basis with the period between polls being determined by the user-defined global
parameter DEAD T (dead timer).

5-4

When specifying the parameters controlling polling levels, the user has the option of accepting the
defaults (see Table 4-2 and 4-3), or selecting specific values in place of these defaults. The user program can set the polling state of a tributary to any state at any time by issuing a latch polling state
control command. The polling state imposed by a control command remains in effect, irrespective of
tributary performance, until polling control is handed back to the polling algorithm by the user program. This is done by issuing an unlatch polling state control command.
Figure 5-3 shows the relationship of the the default values of Q and R for the active, inactive, and
unresponsive polling states.
255r------------,----------------------------------------------_,-------ACTIVE 0=255, R=O

ELIGIBLE FOR
POLLING

u
z
w

(!)

~ 128
(!)

::J
....J

oQ..

NOT POLLED

200ms

1.2sec

2.60sec

DELTA T = 200ms
MK·2642

Figure 5-3

Relationship Between the Default Values for Q and R for the Three
Polling Activity Levels

5-5

Each tributary has Q and R values defined by the user for the active, inactive, and unresponsive polling
states. This allows dynamic modification of the behavior of the polling algorithm. The basic mechanics
of the polling algorithm are:

•

If a tributary always responds to a poll with data, it remains in the active state. The polling
urgency in this case is calculated using the Q and R values specified for the active state.

•

If a tributary responds to a user-defined number of consecutive polls with no data messages
(ACKs only), polling is changed to inactive. The polling urgency is then calculated based on
the Q and R values defined for the inactive state.

•

If a tributary in either the active or inactive states fails to respond (times out) to a predetermined number of consecutive polls, the polling state is changed to unresponsive. The Q
and R values defined for the unresponsive state are used to calculate the polling urgency.

•

If a tributary in the unresponsive state fails to respond to a predetermined number of consecutive polls, the polling state is changed to dead. The user is notified of this transition by a
control response. Polling dead tributaries is very time-consuming because it usually requires
a timeout. Therefore, dead tributaries are not polled on a priority basis. Instead, a global poll
interval is defined for dead tributaries. Each time this timer expires, a single dead tributary
is polled. If at any time a dead tributary responds to a poll with a data message or ACK, its
state is changed to active.

NOTE
A tributary (not in the active polling state) is automatically returned to the active state when it responds to a poll with a valid data message. It also
becomes active when the user program allocates a
transmit buffer to it.

Figure 5-4 is a state diagram describing the transitions between polling states. The actual transitions are
dependent on the particular polling parameters.
The user may control sending of all polls by defining a poll delay interval that must expire before a poll
can be sent.
The program-selectable parameters which pertain to polling are included in Table 4-2. These parameters are set by the user with a write TSS command.
5.2.2 Criteria for Determining Polling Parameters
Although there are no absolute rules for determining polling parameters, there are general guidelines
for deriving them. These guidelines are presented in sections 5.2.2.1 through 5.2.2.4.

5.2.2.1 Determining a, Value for DELTA T - For most multipoint network applications, the default
value of 200 ms for DELTA T is adequate. The default value of 200 ms is the smallest permissible
value for DELTA T and represents the actual time required for the microcode to update the urgencies
of 12 tributaries. However, in specific cases a higher value of DELTA T might be recommended. An
example of this is a network formed by low traffic devices.

5-6

NOTE
The minimum polling interval defines the time required for a tributary to reach the urgency threshold
value of 128. This is the minimum time required to
be eligible for polling. The maximum polling interval
cannot be determined. This is because it is a function
of line speed, message traffic, the number of tributaries in a network, and the polling states of those
tributaries. These variables make it impossible to
predict the time at which any tributary in a network
is polled.

MK-1956

Figure 5-4

State Diagram of Polling State Transitions

5.2.2.2 Determining Values for Q and R - For a given value of DELTA T, the minimum polling interval is 8: function of the user-defined parameters Q and R. For example, if a minimum polling interval of
3.2 seconds is desired for a tributary (assuming DELTA T = 200 ms), the parameters Q = 0, and R =
8 satisfy this requirement. With these values of Q and R, the time to reach maximum polling urgency is

5-7

6.375 seconds (see Figure 5-2). Notice that if Q = 64 and R = 4, the minimum polling interval remains at 3.2 seconds but the maximum polling urgency increases to 9.55 seconds.
NOTE
Reaching maximum polling urgency represents maximum eligibility for polling, but does not guarantee
that a tributary will be polled,
Figure 5-3 graphs the relationship between the default values of Q and R for each of the three polling
states. When all tributaries in a network have the default value for Q and R, and all tributaries are in
the active polling state, the manner of polling is round-robin.
5.2.2.3 Determining a Value for Poll Delay - The user-defined global parameter poll delay imposes a
fixed delay between control station polls. This provides a mechanism for regulating message traffic
without changing the values of Q and R for individual tributaries. During this delay, transmission from
the control station to tributaries is halted for the interval defined by the poll delay timer. This interval
begins when the tributary just polled deselects itself.
The ability to regulate message traffic through a single parameter is valuable in multipoint networks.
This is especially true where DMVl1s are configured together with slower character interrupt communication devices such as DUPlls. The value selected for-poll delay in these circumstances is a function
of the character handling rates of the non-DMVll devices.
In remote multipoint networks ,where the distance between the control station and tributaries varies
significantly, there is a greater chance of transmit and receive errors. This is due to the difference in
communication line settling time in such a network. In such instances, the settling time for the most
distant tributary station should be used for determining a value for poll delay.
For DMVl1-implemented high-speed local networks, this parameter is unnecessary. The default value
(zero) for poll delay is used in these networks.
5.2.2.4 Determining a Value for DEAD T - This global parameter establishes the rate at which dead
tributaries are polled. Dead tributaries are polled, on a round-robin basis, with one tributary polled at
each expiration of the dead tributary timer.
Polling dead tributaries can significantly impact network line utilization. The shorter the period of this
timer - the greater the impact. For a given value of DEAD T, the impact decreases as system line
speed increases. When determining a value for this parameter, the primary goal is to minimize the impact on network line utilization.
The value for DEAD T should be based on the period of the selection interval timer for the specific
application. For example, if the period of the dead tributary timer and the selection interval timer are
equal, only dead tributaries are polled. For most system applications, the period of the dead tributary
should be from three to ten times greater than that of the selection interval timer. This of course depends on line speed. The default value for DEAD T is ten seconds. This is about three times the default
. value for the selection interval timer.
5.3 ERROR COUNTERS
In multipoint networks many tributaries tie to the same transmission line. Because of this, it is more
difficult to determine which link, if any, is causing errors. To aid in troubleshooting, the DMVll maintains extensive error counters. Every DMVl1 in the network (the control station and each tributary)
uses error counters to record errors. This allows user programs at any DMVII in the network to determine overall error rates and to detect a malfunctioning link.

5-8

Data link errors are indicated to the DMVII by DDCMP negative acknowledge messages (NAKs).
Each NAK contains an address field and a reason code that identifies the source and reason for the
NAK. In general, when an error is detected in an incoming message, the station that receives the message sends a NAK to the station that sent the message. By recording NAKs sent and NAKs received,
each point or tributary in the network is able to compile statistics on the condition of the link established between the two stations. DDCMP error recording has been designed so that even if one of the
stations on the link cannot record errors, the other station may be used to record errors for all communications in both directions on the link.
There are three main categories of error counters used by the DMVll; data link counters, station
counters, and threshold counters. Data link counters and threshold counters are maintained for each
tributary/control station pair on a physical link. These counters are located in the tributary status slots
of the data memory (Figure 5-5). Station counters are maintained for the physical link as a whole, and
are located in the global status slots of the data memory (Figure 5-6). Unless otherwise stated, all
counters increment to a maximum value and hold that value until cleared.
5.3.1 Data Link Error Counters
Data link counters are of two types; cumulative and background. The cumulative counters are 8-bit
registers which latch at 255. The background counters are 16-bit registers which latch at 65535. The
cumulative data link counters record and total all occurrences of an error and group them into the following categories.
•
•
•
•
•
•
•

Data errors outbound,
Data errors inbound,
Local reply timeouts,
Remote reply timeouts,
Local buffer errors,
Remote buffer errors,
Selection timeouts.

Background data link counters are used to provide a statistical base for the cumulative error counters
and therefore record:
•
•
•

The number of data messages transmitted,
The number of data messages received, and
The number of selection intervals.

A point-to-point station maintains a single set of data link counters. Multipoint stations (control and
tributary) maintain a separate set of data link counters for each established tributary. Data link
counters are cleared by:
•
•
•

A master clear of the DMVll,
A control command to establish the tributary, or
A user-issued control command to read and clear the TSS error counters.

5.3.1.1 Data Errors Outbound - This 8-bit group counter records NAKs received for data errors occurring on the communications channel outbound from this station. There are three types of outbound
errors for which this counter records NAKs received; header blockcheck (OHBCC), data field blockcheck (ODBCC), and reply response (OREP). Three separate flag bits indicate which type of outbound
error is being counted.
•

OHBCC (outbound header blockcheck) is set when a NAK with a reason code of one is rec~ived for a header block-check error for either data or control messages.

5-9

•

ODBCC (outbound data field blockcheck) is set when a NAK with a reason code of two is
received for a data field block-check error.

•

OREP (outbound reply response) is set when a NAK with a reason code of three is received
for a reply message 'response.
TRIBUTARY STATUS SLOT (TSSI
ADDRESS (OCTALI

RESERVED
RECEIVE THRESHOLD ERRORS

TRANSMIT THRESHOLD ERRORS
SELECTION THRESHOLD ERRORS

7
~

DATA MESSAGES TRANSMITIED

DATA MESSAGES RECEIVED

SELECTION INTERVALS

DATA ERRORS OUTBOUND
RESERVED

I OREP I ODBCC

OHBCC

DATA ERRORS INBOUND
RESERVED

I'REP I'DBCC I'HBCC

LOCAL BUFFER ERRORS
RESERVED

1 I
LBTS

LBTU

REMOTE BUFFER ERRORS
RESERVED

1 I
RBTS

RBTU

SELECTION TIMEOUTS
RESERVED

IRTS

NRTS

LOCAL REPLY TIMEOUTS
REMOTE REPLY TIMEOUTS

MK·1960

Figure 5-5

Data Link and Threshold Error Counters

5-10

GLOBAL STATUS SLOT (GSS)
ADDRESS (OCTAL)

REMOTE STATION ERRORS

I
16

RSEL

LUNDR

RMHFE

ROVRN

LOCAL STATION ERRORS

I
17

RSTR

LOVR

LMRFE

LOVRN

GLOBAL HEADER BLOCK CHECK ERRORS
MAINT. DATA BLOCK CHECK ERRORS
MK-1959

Figure 5-6

Station Error Counters

5.3.1.2 Data Errors Inbound - This 8-bit group counter records occurrences which normally result
from data errors on the communications channel inbound to this station. Three separate bits indicate
specific error types associated with this counter.
•

IHBCC (inbound header blockcheck) is set when messages having header-block check errors
are received. When this error occurs, point-to-point stations and multipoint control stations
send a NAK with a reason code of one. A multipoint control station records this error for the
selected tributary regardless of the address field in the received message. A multipoint tributary records this error only if the address field matches its station address.

•

IDBCC (inbound data field blockcheck) is set when NAKs with a reason code of two are to
be sent for data field block-check errors.

•

IREP (inbound reply response) is set when NAKs with a reason code of three are to be sent
for a reply response.

5.3.1.3

Local Reply Timeouts - This 8-bit counter records occurrences which result from:

•

The loss of c~mmunications between two stations while the one recording this error has data
to transmit, or

•

The choice of an inappropriate value for the reply timer.

Specifically, this error counter records the sending of a REP message.
5.3.1.4

Remote Reply Timeouts - This 8-bit counter records occurrences which result from:

•

The loss of communications between two stations while the remote station has data to transmit, or

•

The choice of an inappropriate value for the remote station reply timer.

Specifically, this counter records ACKs sent in response to a REP. The remote station sent a REP
because it received no acknowledgement for messages it previously sent. The local station received
those messages, but the remote station never received the acknowledgement.

5-11 .

5.3.1.5 Local Buffer Errors - This 8-bit counter records the fact that the user program at the station
recording the error failed to properly allocate receive buffers to data messages from the remote station.
Two separate bits indi~ate the specific errors associated with this counter.
•

LBTU (local buffer temporarily unavailable) is set when a buffer is temporarily unavailable.
This condition indicates that a NAK with a reason code of eight is to be sent.

•

LBTS (local buffer too small) is set when a local buffer is too small for the incoming message. This condition indicates that a NAK with a reason code of 16 is to be sent.
y'

5.3.1.6 Remote Buffer Errors - This 8-bit counter records the fact that the user program at the remote
station failed to properly allocate receive buffers to data messages from the station recording the error.
Two separate bits indicate the specific errors associated with this counter.
•

RBTU (remote receive buffer temporarily unavailable) is set when a NAK with a reason
code of eight is received.

•

RBTS (remote receive buffer too small) is set when a NAK with a reason code of 16 is received.

5.3.1.7
•
•
•

Selection Timeouts - This 8-bit counter records the occurrences which result from:
Loss of communications with a remote station,
Data errors on the communications channel to or from the remote station, and
The choice of an inappropriate value for this station's select timer.

This counter is used only by half-duplex point-to-point or multipoint control stations. Two separate bits
indicate the specific errors associated with this counter.
•

NRTS (no reply to select) is used to record selection intervals in which no transmission is
received from the tributary, and no attempt to transmit is detected. Specifically, it records
the expiration of the select timer without the receipt of a valid control message or header, or
the detection of an attempted transmission.

•

IRTS (incomplete reply to select) is used to record selection intervals which were not properly terminated. Specifically, it records the expiration of the select timer preceded by receipt
of a valid control message, receipt of a valid header, or detection of an attempted transmission. An attempted transmission is indicated by:
The presence of a carrier signal,
The receipt of a DDCMP synchronization sequence, and
The receipt of an SOH, ENQ, or DLE.

5.3.1.8 Data Messages Transmitted - This 16-bit counter records messages transmitted by this station,
and latches at a count of 65535. It can be used as a statistical base when evaluating data errors outbound, local reply timeouts, and remote buffer errors. Messages sent as a result of retransmission are
not included in this count.
5.3.1.9 Data Messages Received - This 16-bit counter records messages received by this station, and
latches at a count of 65535. It can be used as a statistical base when evaluating data errors inbound,
remote reply timeouts, and local buffer errors. Messages received out of sequence or in error are not
included in this count.
5-12

5.3.1.10 Selection Intervals - This 16-bit counter records the number of times this station selects the
other station. It also latches at a count of 65535. Specifically, it records the number of messages transmitted with the select flag on. It is only used by half-duplex point-to-point and multipoint control stations. It can be used as a statistical base when evaluating the number of selection timeouts.
5.3.2 Station Error Counters
Station counters are 8-bit counters which latch at 255 and record unusual occurrences. These occurrences may be the result of:
•

A hardware or software fault at this station,

•

A hardware or software fault at a remote station, or

•

A data error on the communications channels undetected by the header block-check field.

A single set of these counters is used for all tributaries on a multipoint link.
There are four types of station counters:
1.
2.
3.
4.

Remote station errors,
Local station errors,
Global header block-check errors, and
Maintenance data field block-check errors.

Station counters are cleared by:
•
•

A master clear of the DMVll, or
A user-issued control command to read and clear the GSS error counters.

5.3.2.1 Remote Station Errors - This 8-bit counter records occurrences caused by a fault in a remote
station or by an undetected data error on the channel inbound to this station. Four separate bits indicate
the specific errors associated with this error counter.
•

ROVRN (remote receive overrun) is set when a NAK with a reason code of nine is received
for a receive overrun.

•

RMHFE (remote message header format errors) is set when a message is received which has
a header format error. This condition indicates that a NAK with a reason code of 17 is to be
sent.

•

RSEL (remote selection address error) is set when a multipoint control station receives a
message containing an address field which does not match the address of the currently selected tributary. RSEL is a flag used only by multipoint control stations.

•

RSTR (remote streaming tributaries) is set by either one of two events: 1) an implementation-dependent maximum transmission interval is exceeded without releasing the channel
(babbling tributary), or 2) the channel is not released following the end of a selection interval
(streaming tributary).

5.3.2.2 Local Station Errors - This 8-bit counter records occurrences caused by a fault in a local station or by an undetected data error on the channel outbound from this station. Four separate bits indicate the specific errors associated with this error counter.
•

LOVRN (local receive overrun, NAK sent) is set for local station receive overruns. This condition indicates a NAK with a reason code of nine is to be sent.

5-13

•

LOVR (local receive overrun,NAK not sent) is set by a receive overrun when a NAK is not
sent. For a multipoint tributary, this happens if an overrun occurs while receiving a header.
For other stations, this occurs when the station is not in the DDCMP run state.

•

LUNDR (local transmit underruns) is set when a transmit underrun occurs.

•

LMHFE (local message header format error) is set when a NAK with a reason code of 17 is
received to indicate a message with a header format error was sent by this station.

5.3.2.3 Global Header Block-Check Errors - This 8-bit counter records the occurrence of header
block-check errors that are not recorded on a per tributary basis. Specifically, it counts header blockcheck errors for maintenance messages and for messages to tributaries where the address field does not
match the station address.
5.3.2.4 Maintenance Data Field Block-Check Errors - This 8-bit counter records the occurrence of
data field block-check errors for maintenance messages.
,
5.3.3 Threshold Error Counters
Threshold error counters are used to determine if a persistent fault exists. A persistent fault is one
which occurs seven consecutive times. Whenever a threshold counter reaches its maximum value (7),
the user program is notified by a control response.
In the DDCMP run state, threshold counters are cleared when the user is notified. In this way the user
is continually informed of a persistent fault. In the DDCMP ISTRT and ASTRT states, threshold
counters are not cleared when the user is notified. In this way the user is not continually informed of an
inoperative remote station.
A point-to-point station maintains a single set of threshold counters. A multipoint control station maintains a separate set for each tributary. A multipoint tributary maintains a single set unless it supports
mUltiple tributary addresses in which case it maintains a single set for each established tributary address.
There are three types of threshold error counters: transmit, receive, and selection.
5.3.3.1 Transmit Threshold Errors - This 3-bit counter is incremented (if less than seven) in the following instances.
1.

The DMVII is in the ISTRT state when a STRT message is sent,

The DMVII is in the ASTRT state when a STACK message is sent, or

The DMVII is in the run state and a NAK with a reason code other than three (REP response) is received, or when sending a REP message.

The transmit threshold error counter is cleared:
•

Upon entering the ISTRT, ASTRT, or run states.

•

While in the run state one of the following occurs:
A transmit threshold error is reported,
A NAK, ACK, or data message is received acknowledging a new message, or
A NAK, ACK, or data message is received when no messages are outstanding.

5-14

5.3.3.2 Receive Threshold Errors - This 3-bit counter is incremented (if less than seven) when a NAK
with one of the following reason codes is sent.
Reason Code

Description

1
2

Header block-check error.
Data field block-check error.
REP response.
Buffer temporarily unavailable.
, Receive overrun.
Message header format error.

8
9
16
This counter is cleared when:
•

Entering the ISTRT, ASTRT, or run states,

•

A control message with a correct header blockcheck is received without a header format error,

•

A data message with correct header and data field blockchecks is received without a header
format error, or

•

In the run state, a receive threshold error is reported.

5.3.3.3 Selection Threshold Errors - This 3-bit counter is only used by mUltipoint control stations and
half-duplex point-to-point stations. It is incremented (if less than seven) when a selection timeout occurs.
It is cleared upon receipt of a message with the select bit set, or while in the run state and a selection
threshold error is reported.

5.4 DMVll MICROCODE INTERNAL DATA BASE OVERVIEW
Functionally, the DMV 11 internal data base provides the mechanism for managing:
•

The assignment and completion of transmit and receive buffers,

•

The queuing of DMVII responses,

•

The assignment of TSS structures to established tributaries for the storage and maintenance
of tributary and global status information.

A map of this data base is shown in Figure 5-7. The data base is implemented by three basic structures:
•
•
•

Linked lists,
Slot mapping table,
TSS and GSS structures.

Each of these are described below in terms of organization and function.
5.4. t Linked Lists
A linked list is an open-ended data list made up of fixed-length blocks linked by pointers. Each of these
blocks (link blocks), contain seven bytes of data and a one byte pointer to the next link block in the list.
The pointer in the last block in the list is a terminator value. Figures 5-8 and 5-9 illustrate the standard
format for DMVl1 linked-list structures.

5-15

HEXADECIMAL

0000
SCRATCH PADS

16 BYTES

Q-BUS CSRs

8 BYTES

SCRATCH PADS

32 aYTES

OUT NPR ADDRESS

3 BYTES

SCRATCH PAD

1 BYTE

IN NPR ADDRESS

3 BYTES

SCRATCH PAD

BYTE

GLOBAL STATUS SLOT

64 BYTES

SLOT MAPPING TABLE (SMT)

256 BYTES

MICROPROCESSOR STACK

64 BYTES

BUFFER AND OUTPUT QUEUE
98 ENTRIES

8 BYTES/ENTRY

TRIBUTARY STATUS SLOTS
12 ENTRIES

64 BYTES/ENT,RY

10
1B

3B
3B

3C
3F
BO
CO

1 FF

500
800

MK-2495

Figure 5-7

Data Memory Map

A DMV 11 linked list is made up of five kinds of linked lists.
1.

The free linked list - A list of empty link blocks used by the microcode to form the remaining
kinds of linked lists.

The response linked list - A queue of responses for posting to the user program.

The common buffer pool linked list - A list of the accessing information for each receive
buffer assigned to the common pool. There is one link block for each assigned buffer.

Receive buffer linked list - A list of receive buffer accessing information. One of these is
maintained by the microcode for each established tributary having private receive buffers
assigned. There is one link block for each buffer.

Transmit buffer linked list - A list of transmit buffer accessing information. One of these is
maintained by the microcode for each established tributary having transmit buffers assigned.
There is one linked list for each buffer.

S.4.1.1 The Free Linked List - The free linked list from which all other linked lists draw link blocks, is
maintained in the lower section of data memory called the buffer and output queue (BOQ) (Figure 57). These 832 bytes translate into a total of 104 link blocks available for use by the operational linked
lists. In this way, the free linked list functions as a finite resource for the operational linked lists.

5-16

LINK BLOCK
POINTER A

START OF LIST
POINTER

DATA·

LINK BLOCK
POINTER B

DATA

LINK BLOCK
POINTER C

DATA

.E
.F

•N
377

TERMINATOR

DATA

MK·1981

Figure 5-8

DMVll Linked List Structure Format

As previously stated,a linked list is equipped with two list pointers; one that points to the start of the
list and one that points to the end of the list. When a link block is removed from the free linked list, the
start of the list pointer is changed to point to the next available link block in the free linked list. When a
link block is completed by one of the operational linked lists, it is added to the end of the free linked list
and its internal pointer is set to the terminator value of 377 octal. In addition, the internal pointer in the
next to last link block is changed from 377 octal to the address of the link block just added. The startand end-of-list pointers for the free linked list are maintained in the station

ass.

5-17

Link blocks are removed from the free linked list and added to the receive, transmit, or common pool
buffer linked lists when the user program issues control or buffer address/character count commands
for that purpose. Similarly, link blocks are removed from the free linked list and added to the response
linked list when the DMVll microcode posts a response to the user program. If the last link block is
removed from the free linked list, the start of the list pointer is set to the terminator value of 377 octal
to indicate there are no more link blocks available. In this event, the next request for a link block generates the fatal error QUEUE OVERFLOW. For this reason, the buffer allocation strategy for a user
program must be designed to assure an adequate number of link blocks.

LINK POINTER
MESSAGE NUMBER

POINTER TO THE NEXT LINK BLOCK
ODCMP MESSAGE NUMBER

BSEL 3

TRIBUTARY ADDRESS

BSEL 4

BUS ADDRESS

BSEL 5

BUS ADDRESS

BSEL 6

CHARACTER COUNT LOW

BSEL 7

CHARACTER CNT HIGH, BA 16, BA 17

BSEL 2

TYPE CODE AND BA 18-21

MK-2497

Figure 5-9

Standard Link Block

5.4.1.2 The Response Linked List - This linked list functions as a queue of buffer disposition, control,
and information responses to be posted to the user program. The format of the link block for each of
these three responses is shown in Figure 5-8. When preparing a link to convey a control or information
response, the microcode clears all unused bit positions in the link block to zero. However, link blocks
restored to the free linked list remain unchanged.
The start-of-list and end-of-list pointers for the response linked list are maintained in the station ass.
5.4.1.3 Buffer Linked Lists - A buffer linked list is provided for each type of message buffer allocated
by a user program. These are:
•
•
•

Common pool receive buffers,
Private receive buffers, and
Transmit buffers.

Each link block in a buffer linked list provides the location and size of a buffer in main memory.
The Common Buffer Pool Linked List - This linked list provides a queue of receive buffers available to
all established tributaries according to the quota assigned to each tributary.
Common pool buffers are assigned through the buffer address/character count command, and enabled
with tributary quota assignments through the control command (see Section 3.3.3). The start-of-list and
end-of-list pointers for this linked list are maintained in the station ass.
Receive Buffer Linked List - This linked list serves as a queue of private receive buffers. One list is
maintained for each tributary established at a multipoint station. For point-to-point stations, one list is
maintained at each station. The start- and end-of-list pointers for each receive buffer linked list are
maintained in the associated tributary's (or station's) TSS.

5-18

Transmit Buffer Linked List - This list functions as a queue of transmit buffers. One list is maintained
for each tributary established at a multipoint station. For point-to-point stations, one list is maintained
at each station. The start- and end-of-list pointers for each transmit buffer linked list are maintained in
the associated tributary's (or station's) TSS.
A unique feature of this link block is the message number field. When a message is transmitted from a
buffer, the header of that message contains the DDCMP message number (in the message number
field). The microcode uses this field to locate the buffer for a message that has been NAKed after
transmission and, therefore, must be retransmitted.
5.4.2 Slot Mapping Table
Under DDCMP, the 8-bit message header address field permits a maximum of 255 unique tributary
addresses in a multipoint network. However, the DMVII microcode limits the number of established
tributaries to 12. In order to implement DDCMP, a tributary in a DMVl1-based multipoint network
can have a TSS address in the range of 1 to 255. However, only 12 of these tributaries may be established at anyone time.
TSS addresses are assigned at both control and tributary stations through the slot mapping table
(SMT). As shown in Figure 5-7, this table occupies 256 locations in DMVII data memory; one location
for each of the 255 possible tributary addresses, and one location to address the GSS.
The function of the SMT is to map an 8-bit tributary address into one of the 12 available TSS structures. When a tributary is deleted, its TSS and SMT entry is released for reassignment. When 12 tributaries are established and an attempt is made to establish a 13th, a procedural error is posted to the user
program.
5.4.3 TSS and GSS Structures
The TSS and GSS structures occupy separate sections of data memory. The GSS is a single 64-byte
section while the TSS structure consists of twelve 64-byte sections.
5.4.3.1

The Global Status Slot (GSS) - Functionally, the GSS is used to:

•

Maintain control and status information specific to the operation of the microcode,

•

Record event counts and error conditions that are global in nature, and

•

Store global parameters.

The majority of the GSS is devoted to microcode control and status information. A detailed map of the
GSS is shown in Figure 5-10.
Access to the GSS is accomplished on word boundaries. A user program can read any GSS location
through the control command. The content of the addressed location is transferred to the user program
through an information response. A user program can read and clear only GSS station error counters.
The four global parameters (locations 34 through 37) are written by the user program through the control command.
5.4.3.2 Tributary Status Slots (TSS) - A TSS contains four general categories of tributary information (Figure 5-11):
1.
2.
3.
4.

Protocol and tributary status,
Error and statistical counters,
Message exchange variables, and
Polling parameters.

5-19

Protocol and Tributary Status - This category includes information on the tributary's protocol state, its
status with relation to the logical communications line, its protocol status, and its polling status. Tributary polling status is maintained only at a multipoint network control station. Although this information is only pertinent to, and used by the DMVII microcode, it can be read by a user program.
Error and Statistical Counters - These counters provide the user program with a wide range of error
counts, and a set of statistical counts that permit analysis of the meaning of specific error counts. These
counters can be read and cleared by the. user program. The function of each of these counters is described in detail in Section 5.3.
Message Exchange Variables - This category includes a range of variables used by the microcode to
control the transmission and reception of message data. This includes the common buffer pool quota
assigned by the user program.
A group of timers is also included in the message exchange variables. These timers can be preset to a
specific timeout value by the user program, and directly concern message traffic transferred on the
logical link by the associated tributary. These timers are referred to as:
•
•
•
•

Transmit delay timer,
Selection interval timer, *
Maximum transmitted message count,
Babbling tributary timer.

The link management functions performed by these timers is detailed in Chapter 4.
Polling Parameters - These parameters are user-defined values that are used by the polling algorithm
to conduct dynamic polling activity in multipoint networks. The functions performed by the DMVll
polling algorithm, and the criteria for determining the values for each parameter, are discussed in detail
in Section 5.2.

*A timeout value for the selection interval timer is maintained in each tributary's TSS, but the actual timer is maintained in
the GSS.

5-20

GSS
ADDRESS

POLPTR
RCVPTR

RPM CNTR

XMTPTR

TSP

NASP
BUFPTR

S/OF

S/OO

S/OC

(HIGH)

MODEM

UNUSED

CLEAR TO SEND TIMER (LOW)

REMOTE STATION ERRORS

I
16

TIMER STATUS

RSTR

RSEL I RMHFEI ROVRN

LOCAL STATION ERRORS

SIR TIMER (LOW)
7

ACKTIM

(HIGH)

E/OC

(LOW}

FLAG REGISTER "0"

E/OO

ACKTIM

MODE

E/OF

(HIGH)

\ LOVR \ LUNDR\ LMHFE LOVRN

(HIGH)

B/CW TIMER (LOW)

GLOBAL HDR BCC ERRORS
MAINT DATA BCC ERRORS
MK-2489

Figure 5-10

Global Status Slot (Sheet 1 of 2) .

5-21

GSS
ADDRESS

XHDR

(1 )

POLL DELAY TIMER (LOW)

(2)

(3)

(HIGH)

(4)

(5)

DEAD SCAN

(6)

RCVHDR (1)

(3)

(5)

NUMBER OF SYNCS
RESERVED

(4)

CARRIER LOSS TIMER
USYRT HANG TIMER

(2)

POLL UPDATE POINTER

CARRIER WAIT
TIMER COUNTER

DELTA T

(HIGH)

(6)

R TIMER (LOW)

DEAD T

D TIMER (LOW)

(LOW)
(HIGH)

(HIGH)

(LOW)

POLL DELAY

(LOW)
(HIGH)

(HIGH)

MK·2490

Figure 5-10

Global Status Slot (Sheet 2 of 2)

5-22

TSS
ADDRESS

TRIB STATUS FLAGS
TRIB STATUS FLAGS

POLL STATUS FLAGS

POLL RATE (Ri)

RESERVED

COMMON POOL QUOTA

RECEIVE THRESHOLD ERRORS

TRANSMIT THRESHOLD ERRORS
SELECTION THRESHOLD ERRORS

DATA

MESSAGES

TRANSMITTED

IREP I

IDBCC I

IHBCC

LBTS

LBTU

REMOTE BUFFER ERRORS

RBTS I

RBTU

SELECTION TIMEOUTS
RESERVED

OHBCC

LOCAL BUFFER ERRORS

RESERVED

ODBCC I

DATA ERRORS INBOUND

RESERVED

MAX MSG COUNTER

OREP I

RESERVED I

POLL PRIORITY (Vi)

DATA ERRORS OUTBOUND
RESERVED I

POLL STATUS FLAGS

SELECTION
INTERVALS

TRIBUTARY ADDRESS

MESSAGES

RECEIVED

NAK REASON

DATA

IRTS I

NRTS

LOCAL REPLY TIMEOUTS
REMOTE REPLY TIMEOUTS
MK-2722

Figure 5-11

Tributary Status Slot (Sheet 1 of 2)

5-23

TSS
ADDRESS

N HIGHEST MSG NUMBER XMIT'D
A HIGHEST MSG NUMBER ACK'D

DELAY TIMER
31

T NEXT MSG NUMBER TO XMIT
TPTR ADDR OFLNKBK FOR MSG T

X LAST MSG NUMBER XMIT'T

CX (CONTROL X REPLY T/O)

E/OX END OF XMIT BUFFER QUEUE

S/OR START OF RCV BUFFER QUEUE

TRANSMIT

DELAY

-->

I NACTIVE STATE

#T/O

--->

PDEAD STATE

#T/O

--->

DEAD STATE

SELECTION INTERVAL
TIMING COUNTER

TIMER

#NDM

MAXIMUM MESSAGE COUNTER

E/OR END OF RCV BUFFER QUEUE

Q VALUE FOR PDEAD STATE

R VALUE FOR PDEAD STATE

R HIGHEST MSG NUMBER RCV'D

Q VALUE FOR INACTIVE STATE

R VALUE FOR INACTIVE STATE

S/DX START OF XMIT BUF QUEUE

Q VALUE FOR ACTIVE STATE

R VALUE FOR ACTIVE STATE

XPTR ADDR OF LNKBK FOR MSG X

PRESET VALUE FOR TRANSMIT

NO DATA MESSAGE COUNTER

BABBLING TRIBUTARY
TIMING COUNTER

T/O COUNTER

MK-2721

Figure 5-11

Tributary Status Slot (Sheet 2 of 2)

5-24

CHAPTER 6
TECHNICAL DESCRIPTION
6.1 INTRODUCTION
This chapter provides a block diagram functional description of the DMVI1.
The DMVII is basically a 6502 microprocessor with interfaces to the LSI-II bus and the outside
world. The 6502 is supported with 16K bytes of ROM and 2K bytes of RAM. All I/O is memory mapped to the 6502 data bus. The LSI-II interface is made up of three areas:
1.

NPR circuitry - Full I6-bit direct memory access is' allowed on data transferred in and out.
Independant address registers are provided for the in and out NPR addresses.

CSRs - Eight I6-bit CSRs are mapped into the on-board RAM. Any time the LSI-II bus
accesses these registers, the 6502 is halted, the on-board 8-bit RAM is demultiplexed to 16
bits, and I6-bit data is read from or written to the RAM.

Interrupt circuitry - The 6502 can cause interrupts to the LSI-II bus if enabled by the CPU.
Two separate bits allow two levels of interrupt to be initiated.

The outside world interface is handled by a USYRT using a serial transmit and a serial receive line.
The USYRT interfaces directly to the 6502 data bus; activated and monitored by data and status transfers using a predefined address space.
The remaining circuitry which makes up the DMVII is ,used to support the USYRT, the LSI-II interface, the DDCMP protocol, and the modem interfaces.
6.2 LOGIC DESCRIPTION
For discussion purposes, the DMVII logic is divided into the blocks shown in Figure 6-1. The circuitry
and functions represented by each of these blocks is described in Sections 6.2.1 through 6.2.7.
6.2.1 Control and Address Decoder
This block contains the 6502 microprocessor, timing circuits, 6502 data and address interfaces, and
address decoders.
6.2.1.1 The 6502 Microprocessor - The 6502 microprocessor is a 40-pin microprocessor with a full 16bit address bus, an 8-bit bidirectional data bus, and two interrupts.
The 6502 is organized around two primary buses: the address bus and the data bus. The address bus is
used to transfer the address generated by the microprocessor to the address inputs of memory. The data
bus consists of an 8-bit bidirectional data path. All data and instructions are transmitted on this bus.
The 6502 provides a sync-signal to indicate when it is fetching operation code from program memory.
The timing of all data transfers is controlled by a two-phase clock (two nonoverlapping square waves)
referred to as Phase 1 and Phase 2. The address lines and read/write line stabilize during Phase 1 and
data is transferred during Phase 2.

6-1

DATA

ADDR

RECEIVE
FIFO

......

CONTROL

r -

§
LSI·11
BUS
INTERFACE

CONTROL
AND
ADDRESS
DECODER

--,

~--r--"""" MODEM

I INTERFACE I

1~~Ed~;z-t=-a

r-----i~L...MODEM
I
_ _ .J

MEMORY
"------+~~ AND RESET

CONTROL

MK·2523

Figure 6-1

DMV11 Block Diagram

6.2.1.2 Timing Circuits - The source for all the timing signals necessary for the DMV11 is a 20 MHz
crystal. The timing signals produced from this source are:
•

The 6502 microprocessor clock - This clock rate is 1.67 MHz and is generated by dividing
the 20 MHz clock by 6 and then by 2. The 1.67 clock has a duty cycle of 50% ±2 ns.

•

The integral modem receiver 20 times clock - This is a 1.11 MHz clock (20 times 56 KHz
receive clock rate) which is generated by dividing the 20 MHz clock by 9 and then by 2.

•

The integral modem 2 times clock - This is a 111 KHz clock which is generated by dividing
the 1.11 MHz clock by 10.

ROM timing is provided for strobing the 8K by eight ROMS. This signal is produced by delaying the
Phase 2 signal from the 6502 by approximately 160 ns. This allows enough time for the address to
stablize at the ROMs before strobe time.

6.2.1.3 6502 Data and Address Interface - This circuit consists of buffers for the address and data
outputs of the 6502. The buffers have .5 mV low-level inputs so that they are compatible with the 6502
driving requirements.

6-2

6.2.1.4 Address Decoders - Addresses for the address bus come from two sources: 1) the 6502 for
normal microcode execution, and 2) the LSI-II bus for accessing the CSRs. Accessing the CSRs has
priority over the 6502 addressing requirements. CSRs are in RAM and are accessed by the CPU
through the LSI bus interface.
Decoding of the address bus is accomplished by three separate circuits:
1.

Block address decoder - A programmable array logic (PAL) is used to decode the ROM,
I/O, and RAM blocks; and to demultiplex the RAM to I6-bit words when CSRs are accessed by the LSI-II bus.

I/O decoder - This decoder breaks a part of the I/O page up into eight 256-byte sections
when the block address decoder selects I/O. No attempt is made to decode to a specific address within a section. Thus, multiple addresses within a given section decode the same device.

NPR current address decoder - This circuit decodes to a specific address in the RAM address space. Thus, the NPR address registers are mapped directly from RAM. They reflect
the contents of the NPR address locations assigned in RAM (Figure 6-2).
CONTROL STORAGE
MAIN MEMORY
ADDR
DECODE

USYRT
VERSITAl INTF. ADPT

CSR
POINTER

CLOCK
GENERATION

DMA DECODE AND CNTRl

INTERRUPT lOGIC
ADDR
CONTROL

1.67
MHZ

16 BIT ADDRESS BUS
6502
MICROPROCESSOR

20 X 56K
BAUD
RESET
HALT

(8)

DATA BUS

MK·2522

Figure 6-2

Control and Address Decoder

6.2.2 I/O Data Bus
This block contains the USYRT, USYRT control, and line interface control. See Figure 6-3.
6.2.2.1 USYRT - The USYRT is an LSI subsystem for synchronous communications. It provides the
necessary logic support by way of parameter registers for DDCMP. Within this discipline a wide range
of support such as programmable error detection, character recognition, complete serialization, deserialization, and buffering of data is provided.
6.2.2.2 USYRT Control - This circuit consists of a 74LS245 data transceiver, a 74LS373 tristate input data latch, a 74LS244 tristate output data buffer, a 74LS373 tristate address latch, and three

6-3

74LS74 controlling flip-flops and associated gates. For discussion, the operation of the USYRT control
logic is divided into write and read operations. See Figure 6-4.
Write - The 6502 asserts the address, selects the USYRT, and generates the write signal approximately
140 ns after Phase 1 high is asserted. The data is available from the 6502 approximately 115 ns after
Phase 2 high is asserted. The USYRT on the other hand, requires data 50 ns prior to the assertion of
data port enable (DPENA). To achieve the necessary timing relationship, the address and data are
latched into buffers and strobed into the USYRT by the controlling flip-flops which are clocked by
signals generated from Phase 1 and Phase 2 timing. Phase 2 is used to gate DPENA to guarantee the
USYRT minimum requirement of 250 11s for DPENA.
Read - Again the 6502 asserts the address and selects the USYRT as in a write cycle. The USYRT is
strobed by. the controlling flip-flops and data is made available from the USYRT. In a read operation,
the address select lines must be held for 30 ns after DPENA (the 6502 does not guarantee this). Therefore, the address is latched when Phase 2 high is asserted.

SWITCH
LOGIC

(8)

B01

(8)

B02

~TA(N

SELECT

STATUS(!;)

USYRT
CONTROL

USYRT

II"'"

TSO

R/W

BUFF

- -

PIA
6522

TSO

"'"

ADDRESS(3V

ADDRESS (3) .;;;

MK-2499

Figure 6-3

I/O Data Bus

6-4

WRITE
80 1

80 2

DO 2H

I
I

NO 2L

ADD RESS

NO 2H

READ

~LATCHED

VALID AT USYRT

I
I

~LATCHED

I
I

VALID AT USYRT

lI'I

USY RT SELH
READ L
R/W
OATA FROM 6502

WRITE L
~LATCHED

OPE NA
USY RT WRT H

VALID

DATA TO 6502 I
"- VALID ~

I
MK-2507

Figure 6-4

USYRT Timing Diagram

6.2.2.3 Line Interface Control - The line interface control section of logic can be broken into two subsections: 1) switch logic, and 2) programmable interface adapter.
1.

Switch logic - This section consists of two sets of switches and their associated buffers. One
set of switches has its configuration latched into its buffer at boot time. The configuration of
the other set of switches is latched at DDCMP interface selection time.

Programmable interface adapter (also referred to as VIA) - This circuit consists of a 6522
chip and is used to control and monitor the various interface signals to the modem interface
logic.

Referring to the 6522, the PB section and bit 0 of the PA section are used as an output register only.
Bits one through seven of the PA section are used as an input register. CAl and CA2 are used to monitor, by way of the 6502 interrupt, modem ready high and clear to send high. PB7 is used to generate
modem clocks when self-testing with loop back connectors. CB 1 is used to produce eight clock pulses at
a time when instructed to do so by the 6502 microcode. These clock pulses are used to flush the USYRT receiver of data after carrier drops.
6.2.3 DMVll Memory
This block may be divided into three sections as follows.
1.
2.
3.

ROM control storage,
RAM,
NPR in/out registers.

6.2.3.1 ROM Control Storage - ROMS are l}sed for storing operation codes for the 6502 microprocessor.
In order to provide the most immediate access to data for the 6502, 200 ns ROMs are used and the
ROM clock is continuously applied to the chip enable (CE) pill of the ROM. 74S24I buffers are used
on the output so that no more than 9 ns additional delay is introduced.

6.2.3.2 RAM - This is the data memory for the DMVI1. It is organized functionally as shown in
Figure 6-5. The hardware organizes the RAM into even and odd sections for the sole purpose of having
I6-bit CSRs. When CSRs are accessed from the LSI-II bus, even, odd, or both sections of the RAM·
are enabled. Two 74LS245 transceivers are used to enable and direct data to and from the LSI-II bus.
The other two 74LS245 transceivers are used for drive buffering and to disable the RAM from the 8-bit
microprocessor data bus when the CSRs are accessed by the LSI-II bus. The microprocessor is halted
when the CSRs are accessed by the LSI-II bus.
6.2.3.3 NPR In/Out Registers - This circuitry consists of two I6-bit registers (one for address in, and
one for address out), and two I6-bit registers (one for data in, and one for data out). Extended address
capabilities are included in two scratchpad registers which are four words deep by four bits wide.
The microprocessor loads the appropriate NPR address register (in or out) to set up the address for an
NPR data transfer. This address is then enabled onto the LSI-II bus during the address enable cycle.
During a read cycle, the data-in register is loaded from the LSI-II bus and read by the 6502. During a
write cycle, the data-out register is loaded by the 6502 and read by the LSI-II bus.

6-6

HEXADECIMAL

0000
SCRATCH PADS

16 BYTES

Q-BUS CSRs

8 BYTES

SCRATCH PADS

32 BYTES

OUT NPR ADDRESS

3 BYTES

SCRATCH PAD

1 BYTE

IN NPR ADDRESS

3 BYTES

SCRATCH PAD

BYTE

GLOBAL STATUS SLOT

64 BYTES

SLOT MAPPING TABLE (SMT)

256 BYTES

MICROPROCESSOR STACK

64 BYTES

10
1B

3B
3B

3C
3F

1 FF
500

BUFFER AND OUTPUT QUEUE

98 ENTRIES

8 BYTES/ENTRY

TRIBUTARY STATUS SLOTS
12 ENTRIES

64 BYTES/ENTRY

800
MK·2495

Figure 6-5

Data Memory Organization

6.2.4 LSI-II Bus Interface
The circuitry in this block interfaces the LSI-II bus to the 6502 microprocessor (see Figure 6-6). It
consists primarily of the:

•
•
•
•

LSI-II bus DAL interface,
CSR controller,
Interrupt controller, and
NPR controller.

6.2.4.1 LSI-II Bus DAL Interface - This circuit consists of four DC005 chips which interface the
LSI-II data and address lines to the DMVI1. The device address of the DMVII, which may be anywhere in the I/O page, and its associated vector address, is selected by switches on the input to the
DC005 chips.

The DC005s are initially in the receive mode (receiving from the LSI-II bus) in anticipation of an
address match from the LSI-II bus. When a match occurs, the collector-ored match lines go high and
enable the CSR control circuit. In addition to detecting an address match, the DC005s in the receive
mode pass address or data to the DAL lines. In the transmit mode, the DC005s pass data from the
DAL lines to the LSI-II bus.

6-7

LSI-11 BUS
INTERFACE

INTERRUPT
LOGIC AND
CONTROL
DCOOS

CONTROL
NPR
CONTROLLER

DCOOS's

::J

INTERNAL DATA/ADDRESS BUS (16)

(3)

RPLY
CSR
CSR
CONTROLLER

OUT LB
OUT HB
IN WORD

MK·2498

Figure 6-6

LSI-II Bus Interface

6.2.4.2 CSR Controller - This circuit consists of a DC004 which:
•

Supplies outputs which indicate when CSRs are selected. CSRs are decoded when the enable
pin is asserted high and BYSNC strobes on its negative edge.

•

Supplies outputs indicating when a word of data is to be placed on the LSI-II bus, or when a
byte or word of data is to be read from the bus. Byte operations are controlled by the OUT
HB and OUT LB signals.

•

Asserts BRPLY approximately 30 ns after information is placed on the LSI-II bus. BRPL Y
is then applied to a sequencer which halts the 6502 and accesses the particular CSR mapped
in the RAM.
-

•

Applies the BRPLY from the sequencer to the LSI-II bus by the LSI-II control-line interface.

6.2.4.3 Interrupt Controller - This circuit consists of a DC003 interrupt controller chip and two
74LS74 flip-flops. The DC003 is used in a typical manner for interrupt servicing of the LSI-II bus. The
two flip-flops hold the interrupt request (one for A and one for B) until it is serviced. When either
request is serviced, both flip-flops are cleared by the vector signal.

6-8

6.2.4.4 NPR Controller - The DCa lOis used in this application for doing direct memory accesses to
the LSI-II memory. Only single NPRs are allowed; HOG mode is not implemented. A description of
the NPR operation follows.
The microcode sets up the NPR current address and data-out registers, and then sets the A flip-flop by
writing to the NPR register with bit 6 equal to zero. Once the NPR is initiated, the OCala handles the
sequence of enabling appropriate registers to transmit or receive data from the LSI-II bus. This operation is sequenced by the 5 MHz clock input to the OCala.
When the NPR is honored, the leading edge of RPL Y releases the NPR so that a second request does
not occur. The trailing edge of RPL Y sets NPR busy H to zero to indicate that the NPR transfer is
complete. However, when doing data-out transfers, the NPR data-out register must not be updated for
100 ns after the trailing edge of RPL Y in order to comply with LSI-II bus specifications. The microcode can immediately service the data-in register when NPR busy H is cleared during a data-in transfer.
The NPR abort timer is used to ensure that an NPR transfer does not take more than 16 p.s. If 16
are exceeded, the transfer is aborted. The timer is set each time an NPR is initiated.

p. s

6.2.5 Memory and Reset Control
CSR access control allows the LSI-II bus to access the CSRs. The operation is as follows.
1.

The CSR controller (Section 6.2.4.2) asserts the CSR L signal when a CSR is selected. This
signal is used by the processor halt circuit to halt the microprocessor on the next Phase 2
cycle if a write is not in progress. When the processor has halted, the 74LSI64 shift register
is enabled.

When the first output of the shift register is true, the appropriate CSR address is selected
and the direction of transfer is determined by the state of the WRT RAM L signal from the
PAL. WRT RAM L sets the direction of the RAM transceivers (Section 6.2.3.2).

During the next Phase 2 cycle, the CSR is either read and its contents placed onto the LSI11 bus, or the data on the LSI-II bus is written into the CSR.

The next Phase 2 cycle terminates the write cycle if in the write mode, and asserts BRPL Y to
the LSI-II bus.

After RPL Y from the DC004 drops, the microprocessor address and data bus are again controlled by the 6502. When CSR select is dropped, the microprocessor resumes operation.

Memory and reset control also generates signals for master resetting the DMVII and halting the microprocessor.
6.2.6 Modem Interface
The modem interface consists of line receivers and drivers for all modem data and control signals. The
interface supports RS-232-C, RS-423-A, V.35, and the integral modem. Circuitry to accommodate internalloopback for test purposes is also provided. Because the DMVII supports RS-423-A for category
1 signals (except test mode and ring), dummy generators are used for the following signals.
•
Select frequency,
•
Terminal in service,
•
New signal,
•
SRTS,
•
Remote loop,
•
Local loop, and
•
Select standby.

6-9

Only one interface can be enabled at a time. The modem interface select circuit enables an interface as
selected by the interface select switch. On power-up and during any reset operation, the selected interface is disabled and loopback is selected until deselected by the microcode (Section 6.2.2.3).
Interface to the outside world is implemented with two 40-pin Berg connectors. J2 is used for RS-232-C
and RS-423-A with a BC55H-type cable. Jl is used for V.35 with the BC05Z cable or for the integral
modem with the BC55F cable.'
The modem interfaces all have a null clock that is switch selectable for speeds of 56K bls or 19.2K bls
and controlled by the PIA.
6.2.7 Integral Modem
The integral modem is used for local communications and is transformer-coupled to twin ax or triax
cables for common mode rejection and common mode voltages up to 500 V. For discussion purposes,
the integral modem is described in two sections: receive (Figure 6-7) and transmit (Figure 6-8).
6.2.7.1 Receive - The received data enters the modem through an isolation transformer whose output
is directed to a differential amplifier to eliminate common mode noise. The amplifier's second stage
uses an active Buterworth filter with an added passive filter for high and low cutoff. The filter's complimentary outputs are input to a comparator which detects zero crossover. Positive and negative transitions from the comparator clock the UP and DOWN flip-flops. All clocking is done at a clock rate 20
times the bls rate and the UP and DOWN flip-flops latch until cleared by the transitions (TRANS)
flip-flop.
When either the UP or DOWN flip-flop is set, the next clock pulse loads the transitions (TRANS) flipflop which then clears the UP or DOWN flip-flop and holds it clear for one clock time. The clock input
to the TRANS flip-flop and receive counter (REC CNTR) is 20 times the data-rate clock time.
The REC CNTR is clocked at half clock time (or inverted 20X clock), and counts 16 clock times and
sets the 314 time flip-flop. The counter is loaded if the TRANS flip-flop is set and 16 clocks have
occurred since the last load. The counter enable is'true except in an overflow condition or when operating in half-duplex mode with the transmitter active.
When 3/4 T is set, and the time between transitions is greater than 16 clock "times, the IDATA flip-flop
is clocked to one. If the transition time is less than 16 clock times when 314 T is set, the IDAT A flipflop is clocked to a zero. The minimum time between transitions is .05 to .10 bit times as determined by
the TRANS flip-flop clearing the UP and DOWN flip-flops. The next 3/4 T clock loads IDATA into
the RI DATA flip-flop. The next 3/4 T clock ANDs RI DATA with IDATA, and if IDATA is zero,
sets the I CARRIER flip-flop. IDATA is input to the receive FIFO and I CARRIER is gated with
LINE UNIT STEP to become GRX CLK.
The overflow flip-flop is set when no transition occurs within one and one-half bit times. Overflow then
sets IDAT A which allows the next clock pulse to clear the RI DATA and I CARRIER flip-flops until
the next sequence of one followed by two zeros occurs.
6.2.7.2 Transmit - The transmit circuit encodes the data into diphase space; in a square wave sequence. The output is 6 V peak-to-peak into a 50 ohms load and does not exceed 15 V peak-to-peak into
an open circuit.
RTS allows TI CLK to set the ICS flip-flop. When the ICS flip-flop is set, the encoder flip-flop (ENC)
is allowed to toggle with each data or TI CLK. The encoded output feeds a bipolar line driver that
generates an ac signal with zero crossover points. The line driver output is connected to the protection
transformer.

6-10

The + 5 V low circuit turns off the transistors on low logic power to keep the transmitter from generating noise or from loading the line. During power-up, this circuit keeps the modem in the disabled state
for several milliseconds to prevent the transmission of nonsense characters that would interfere with
transmission in progress on a multipoint line.
The transmitter is disabled when line units are not transferring data. The transmitter does not load the
line when power is off.
BERG
CONN

~!~A
IN

FFs
DIFFERENTIAL
AMPLIFIER

-II

ISOLATION
TRANSFORMER _

ZERO

DIFF : FILTER _
I

DETECT
CROSS·
OVER
-

t----t1 )UP

DOWN

~&...._-

TRANS

COMPARATOR

20X ClK H

FF
OVF

REC
CNTR

RI DATA
SYNC
UP
&
DATA

x::~-----

------

CARRIER

CO~--~

20~ ClK H

I---

*T
U
MK-2500

Figure 6-7

Integral Modem Receive

6-11

CLK

RTS

TX DATA

ICS

L...0

ENC

CLR
LOOPBACK

TI CLK

f
I

BI POLAR
LINE
DRIVER

roo-

--+
XFORMER
+5V LOW &
ENABLE

- .......DATA
OUT
- .......

+5V

MK·2503

Figure 6-8

Integral Modem Transmit

6-12

CHAPTER 7
SERVICE

7.1 SCOPE
This chapter provides information for servicing the DMV 11. It includes the maintenance philosophy,
troubleshooting techniques in a multipoint environment, maintenance functions, preventive maintenance, and' corrective maintenance. The section on troubleshooting techniques in a multipoint environment includes:
•

The general overall approach to multipoint troubleshooting.

•

Some common problems associated with different mUltipoint network configurations.

•

The use of error counters and other information for isolating problems to a specific portion of
the physical link.

The corrective maintenance section contains brief descriptions of the diagnostics associated with the
DMVII.

7.2 MAINTENANCE PHILOSOPHY
The field replaceable unit (FRU) for the DMVll is either a module (M8053 or M8064 microcontroller/line unit) or cable. Training of field service personnel is directed to functional and application troubleshooting, using diagnostics, for fault isolation to the FRU. Spare parts for module repair
are not stocked in the field. Typical applications of the DMVll do not permit lengthy troubleshooting
sessions, and component troubleshooting/repair requires at least a 16-channellogic analyzer.

7.3 TROUBLESHOOTING TECHNIQUES FOR MULTIPOINT
Because of the complexity of some multipoint network configurations, there is a potential for using
valuable time in trying to isolate a problem. For this reason, troubleshooting techniques for multipoint
networks differ from those for point~to-point networks.
The following sections discuss these troubleshooting techniques m terms of approach and error
counters.

7.3.1 Approach
Before attempting any corrective measures, it is important to get some basic information about the
network configuration and the nature of the problem. This information can be obtained by querying the
user and by referring to the topology diagram for the network. The topology diagram is generated at
installation time and is maintained by the field service representative. The flow chart (Figure 7-1) illustrates a typical approach to troubleshooting from the time a service call is placed, until corrective maintenance is begun. This procedure should be followed to help isolate a' failing tributary before anyone is
dispatched to a site.
7-1

CALL RECEIVED
FROM CONTROL
STATION

......._~YES

GATHER THE FOLLOWING
INFORMATION FROM THE
FAILING TRIBUTARY

CALL MODEM
SERVICE REP.

RELOAD TRIB SOFTWARE
AND INITIALIZE POLLING
FROM CENTRAL STATION

RX PROBLEM
IN MODEM OR
LINE. CALL SERVICE

GO TO FAILING
STATION

MK·2398

Figure 7-1

Example of a Typical Isolation Flow Diagram (Sheet 1 of 5)

7-2

RELOAD SOFTWARE AND
RESTART AT CONTROL
AND TRIB STATIONS

CALL MODEM
SERVICE REP.

END
NO

GO TO CONTROL
STATION

CALL MODEM
SERVICE REP.

TX PROBLEM IN
MODEM OR LINE.
CALL SERVICE

MK-2399

Figure 7-1

Example of a Typical Isolation Flow Diagram (Sheet 2 of 5)

7-3

RX PROBLEM IN
MODEM OR LINE
CALL SERVICE

YES

CHECK FOR STREAMING
TRIB. CALL SITES TO
OBSERVE RTS ON MODEM

MODEM OR LINE
PROBLEM CALL
SERVICE

GO TO SITE THAT
CAUSED CONDITION AND
RESTORE ALL OTHERS

MK·2400

Figure 7-1

Example of a Typical Isolation Flow Diagram (Sheet 3 of 5)

7-4

GO TO FAILING
STATION

CALL MODEM
SERVICE REP.

YES
TX PROBLEM IN
MODEM OR LINE
CALL SERVICE
MK-2401

Figure 7-1

Example of a Typical Isolation Flow Diagram (Sheet 4 of 5)

7-5

RELOAD SOFTWARE AND
RESTART CONTROL

BYPASS SPLITTER OR
USE DIFFERENT PORT

CALL MODEM
SERVICE REP.

HAVE SPLITTER OR
MODEM REPLACED

INITIATE CORRECTIVE
MAINTENANCE

CALL
SUPPORT

MK·2402

Figure 7-1

Example of a Typical Isolation Flow Diagram (Sheet 5 of 5)

7.3.2 Error Counters
In multipoint networks many tributaries tie to the same transmission line. Because of this, it is more
difficult to determine which link, if any, is causing errors. To aid in troubleshooting, the DMVll uses
error counters. Every DMVII in the network (the control station and each tributary) uses error
counters to record errors. This allows user programs at any DMV II in the network to determine overall
error rates and to detect a malfunctioning link.
The main way in which errors are indicated to the DMVII is by DDCMP negative acknowledge messages (NAKs). Each NAK contains an address field and a reason code that identifies the source and
reason for the NAK. In general, when an error is detected in an incoming message, the station that
receives the message sends a NAK to the station that sent the message. By recording NAKs sent and
NAKs received, each point or tributary in the network is able to compile statistics on the condition of
the link established between the two stations. DDCMP has been designed so that even if one of the
stations on the link cannot record errors, the other station may be used to record errors for all communications in both directions on the link.
There are three main categories of error counters used by the DMVll; data link counters, station
counters, and threshold counters. Data link counters and threshold counters are maintained for each
tributary/control station pair on a physical link. These counters are located in the tributary status slots
(TSS) of the data memory (Figure 7-2). Station counters are maintained for the physical link as a
whole, and are located in the global status slots (GSS) of the data memory (Figure 7-3). The information gained by checking error counters may be helpful in pinpointing a problem area.
7.3.2.1 Data Link Error Counters - Data link counters are of two types; cumulative and background.
The cumulative counters are 8-bit counters which latch at 255. The background counters are 16-bit
counters which latch at 65535. The cumulative data link counters record and total all occurrences of an
error and group them into the following categories.
•
•
•
•
•
•
•

Data errors outbound,
Data errors inbound,
Local reply timeouts,
Remote reply timeouts,
Local buffer errors,
Remote buffer errors,
Selection timeouts.

Background data link counters are used to provide a statistical base for the cumulative error counters
and therefore record:
•
The number of data messages transmitted,
•
The number of data messages received, and
•
The number of selection intervals.
A point-to-point station maintains a single set of data link counters. Multipoint stations (control and
tributary) maintain a separate set of data link counters for each established tributary. Data link
counters are cleared by:
•
•
•

A master clear of.the DMVII,
A control command to establish the tributary, or
A user-issued control command to read and clear the TSS error counters.

Data Errors Outbound - This 8-bit group counter records NAKs received for data errors occurring on
the communications channel outbound from this station. There are three types of olltbound errors for
which this counter records NAKs received; header blockcheck (OHBCC), data field blockcheck
(ODBCC), and reply response (OREP). Three separate flag bits indicate which type of outbound error
is being counted.

7-7

•

OHBCC (outbound header blockcheck) is set when a NAK with a reason code of one is received for a header block-check error for either data or control messages.

•

ODBCC (outbound data field blockcheck) is set when a NAK with a reason code of two is
received for a data field block-check error.

•

OREP (outbound reply response) is set when a NAK with a reason code of three is received
for a reply message response.

TRIBUTARY STATUS SLOT (TSS)
ADDRESS (OCTAL)

RESERVED
RECEIVE THRESHOLD ERRORS

TRANSM IT THRESHOLD ERRORS
SELECTION THRESHOLD ERRORS

7
I--

DATA MESSAGES TRANSMITTED

po-...

DATA MESSAGES RECEIVED

SELECTION INTERVALS

--.

DATA ERRORS OUTBOUND
RESERVED

1 I
OREP

ODBCC

OHBCC

DATA ERRORS INBOUND
RESERVED

IIREP IIDBCC IIHBCC

LOCAL BUFFER ERRORS

RESERVED

LBTS I LBTU

REMOTE BUFFER ERRORS
RESERVED

I RBTS I RBTU

SELECTION TIMEOUTS
RESERVED

IIRTS

I NRTS

LOCAL REPLY TIMEOUTS
REMOTE REPLY TIMEOUTS
MK·1960

Figure 7-2

Data Link and Threshold Error Counters

7-8

GLOBAL STATUS SLOT (GSS)
ADDRESS (OCTAL)

REMOTE STATION ERRORS

I
16

RSEL

LUNDR

RMHFE

ROVRN

LOCAL STATION ERRORS

I
17

RSTR

LOVR

LMHFE

LOVRN

GLOBAL HEADER BLOCK CHECK ERRORS
MAINT. DATA BLOCK CHECK ERRORS
MK·1959

Figure 7-3

Station Error Counters

Data Errors Inbound - This 8-bit group counter records occurrences which normally result from data
errors on the communications channel inbound to this station. Three separate bits indicate specific error
types associated with this counter.
•

IHBCC (inbound header blockcheck) is set when messages having header block-check errors
are received. When this error occurs, point-to-point stations and multipoint control station~
send a NAK with a reason code of one. A multipoint control station records this error for the
selected tributary regardless of the address field in the received message. A multipoint tributary records this error only if the address field matches its station address.

•

IDBCC (inbound data field blockcheck) is set when NAKs with a reason code of two are to
be sent for data field block-check errors.

•

IREP (inbound reply response) is set when NAKs with a reason code of three are to be sent
for a reply response.

Local Reply Timeouts - This 8-bit counter records occurrences which result from:
•

The loss of communications between two stations while the one recording this error has data
to transmit, or

•

The choice of an inappropriate value for the reply timer.

Specifically, this error counter records the sending of a REP message.
Remote Reply Timeouts - This 8-bit counter records occurrences which result from:
•

The loss of communications between two stations while the remote station has data to transmit, or

•

The choice of an inappropriate value for the remote station reply timer.

Local Buffer Errors - This 8-bit counter records the fact that the user program at the station recording
the error failed to properly allocate receive buffers to data messages from the remote station. Two separate bits indicate the specific errors associated with this counter.
•

LBTU (local buffer temporarily unavailable) is set when a buffer is temporarily unavailable.
This condition indicates that a NAK with a reason code of eight is to be sent.

•

LBTS (local buffer too small) is set when a local buffer is too small for the incoming message. This condition indicates that a NAK with a reason code of 16 is to be sent.

Remote Buffer Errors - This 8-bit counter records the fact that the user program at the remote station
failed to properly allocate receive buffers to data messages from the station recording the error. Two
separate bits indicate the specific errors associated with this counter.
•

RBTU (remote receive buffer temporarily unavailable) is set when a NAK with a reason
code of eight is received.

•

RBTS (remote receive buffer too small) is set when a NAK with a reason code of 16 is received.

Selection Timeouts - This 8-bit counter records the occurrences which result from:
•
•
•

Loss of communications with a remote station,
Data errors on the communications channel to or from the remote station, and
The choice of an inappropriate value for this station's select timer.

This counter is used only by half-duplex point-to-point or multipoint control stations. Two separate bits
indicate the specific errors associated with this counter.
•

•

Data Messages Transmitted - This 16-bit counter records messages transmitted by this station, and
latches at a count of 65535. It can be used as a statistical base when evaluating data errors outbound,
local reply timeouts, and remote buffer errors. Messages sent as a result of retransmission are not included in this count.
Data Messages Received - This 16-bit counter records messages received by this station, and latches at
a count of 65535. It can be used as a statistical base when evaluating data errors inbound, remote reply
timeouts, and local buffer errors. Messages received out of sequence or in error are not included in this
count.

7-10

Selection Intervals - This 16-bit counter records the number of times this station selects the other station. It also latches at a count of 65535. Specifically, it records the number of messages transmitted
with the select flag on. It is only used by half-duplex point-to-point and multipoint control stations. It
can be used as a statistical base when evaluating the number of selection timeouts.
7.3.2.2 Station Error Counters - Station counters are 8-bit counters w'hich latch at 255 and record
unusual occurrences. These occurrences may be the result of: '
•

A hardware or software fault at this station,

•
•

A hardware or software fault at a remote stati~>n, or
A data error on the communications channel undetected by the header block-check field.

A single set of these counters is used for all tributaries on a multipoint link.
There are four types of station counters:
1.
2.
3.
4.

Remote station errors,
Local station errors,
Global header block-check errors, and
Maintenance data field block-check errors.

Station counters are cleared by:
•
•

A master clear of the D MV 11, or
A user-issued control command to read and clear the GSS error counters.

Remote Station Errors - This 8-bit counter records occurrences caused by a fault in a remote station or
by an undetected data error on the channel inbound to this station. Four separate bits indicate the specific errors associated with this error counter.
•

ROVRN (remote receive overrun) is set when a NAK with a reason code of nine is received
for a receive overrun.

•

RMHFE (remote message header format errors) is set when a message is received which has
a header format error. This condition indicates that a NAK with a reason code of 17 is to be
sent.

•

RSEL (remote selection address error) is set when a multipoint control station receives a
message containing an address field which does not match the address of the currently selected tributary. This error is recorded only by multipoint control stations.

•

RSTR (remote streaming tributary) is set by either one of two events: 1) an implementationdependent maximum transmission interval is exceeded without releasing the channel (babbling tributary), or 2) the channel is not released following the end of a selection interval
(streaming tributary).

Local Station Errors - This 8-bit counter records occurrences caused by a fault in a local station or by
an undetected data error on the channel outbound from this station. Four separate bits indicate the
specific errors associated with this error counter.
•

LOVRN (local receive overrun, NAK sent) is set for local station receive overruns. This condition indicates a NAK with a reason code of nine is to be sent.

7-11

•

LOVR (local receive overrun, NAK not sent) is set by a receive overrun when a NAK is not
. sent. For a multipoint tributary, this happens if an overrun occurs while receiving a header.
For other stations, this occurs when the station is not in the DDCMP run state.

LUNDR (local transmit underruns) is set when a transmit underrun occurs.

•

LMHFE (local message header format error) is set when a NAK with a reason code of 17 is
received to indicate a message with a header format error was sent by this station.

Global Header Block-Check Errors - This 8-bit counter records the occurrence of header block-check
errors that are not recorded on a per tributary basis. Specifically, it counts header block-check errors
for maintenance messages and for messages to tributaries where the address field does not match the
station address.
Maintenance Data Field Block-Check Errors - This 8-bit counter records the occurrence of data field
block-check errors for maintenance messages.
7.3.2.3 Threshold Error Counters - Threshold error counters are used to determine if a persistent fault
exists. A persistent fault is one which occurs seven consecutive times. Whenever a threshold counter
reaches its maximum value (7), the user program is notified by a control response.
In the DDCMP run state, threshold counters are cleared when the user is notified. In this way the user
is continually informed of a persistent fault. In the DDCMP ISTRT and ASTRT states, threshold
counters are not cleared when the user is notified. In this way the user is not continually informed of an
inoperative remote station.
A point-to-point station maintains a single set of threshold counters. A multipoint control station maintains a separate set for each tributary. A multipoint tributary maintains a single set unless it supports
multiple tributary addresses in which case it maintains a single set for each established tributary address.
There are three types of threshold error counters: transmit, receive, and selection.
Transmit Threshold Errors - This 3-bit counter is incremented (if less than 7) in the following instances.
1.

The DMVII is in the ISTRT state when a STRT message is sent,

The DMVII is in the ASTRT state when a STACK message is sent, or

The DMVII is in the run state and a NAK with a reason code other than three (REP response) is received, or when this station sends a REP message.

The transmit threshold error counter is cleared:
•

Upon entering the ISTRT, ASTRT, or run states.

•

While in the run state one of the following occurs.
A transmit threshold error is reported,
A NAK, ACK, or data message is received acknowledging a new message, or
A NAK, ACK, or data message is receiv'ed when no messages are outstanding.

7-12

Receive Threshold Errors - This 3-bit counter is incremented (if less than seven) when a NAK with one
of the following reason codes is sent.
Reason Code

Description

Header block-check error.
Data field block-check error.
REP response.
Buffer temporarily unavailable.
Receive overrun.
Message header format error.

2
3
8
9

This counter is cleared when:
•

Entering the ISTRT, ASTRT, or run states,

•

A control message with a correct header blockcheck is received without a header format error,

•

A data message with correct header and data field blockchecks is received without a header
format error, or

•

In the run state, a receive threshold error is reported.

Selection Threshold Errors - This 3-bit counter is only used by multipoint control stations and halfduplex point-to-point stations. It is incremented (if less than seven) when a selection timeout occurs.
It is cleared upon receipt of a message with die select bit set, or while in the run state and a selection
threshold error is reported.

7.3.3 Error Counter Analysis
In most applications the software operating system records all the error counters, but does not attempt
to analyze or take any particular action of its own as a result of any specific errors.
The system manager or another operator instructs the software to retrieve the counters. The counters
are analyzed by the operator or system manager and then the software is instructed to perform a specific function relative to the counter indications.
For information on retrieving the counters, refer to the system-specific DECnet System Manager's
Guide or consult the network manager.
The following example serves to illustrate how the counters can be used in diagnosing a system failure
(refer to Figure 7-4). A user should keep in mind that DCLT also allows access to error counters. See
Section 7.6.5.
Assume that a full-duplex multipoint network is made up of seven tributaries and a control station as
shown in Figure 7-4. The type of electrical interface (EIA RS-232/RS-449, V.35, integral modem) is
not important in this example. The system manager at the control station notices that data transfers
over the network appear to be "sluggish." Some standard file transfers are taking a longer time than
usual to complete. (Note that in some cases this could be caused by a sudden increase in traffic on the
network.) The problem appears to be intermittent in nature since no threshold errors have occurred and
data is still being transferred between all tributaries. The system manager examines the error counters
at the control station for tributary seven. They are as follows.

7-13

CONTROL

r ----------h
,
'
I

TSS 1

TSS 4

TSS 2

TSS 5

I INTERNAL DMV11

to----......---....... I NETWORK DATA

I ....T_S_S_3_......._TS_S_6_....... ' BASE

I
L

TSS 7
RCV

LOCATION OF
CABLE FAULT
(FOR EXAMPLE
A HIGH RESISTANCE
CONNECTION)

- XMT

.-.J

XMT

I RCV

TRIB
1

XMT

I RCV

1RCV

XMT

XMTI RCV

XMT

IRCV

XMT

I RCV

XMTI RCV

TRIB

7
MK·2649

Figure 7-4

Full-Duplex Seven Tributary Multipoint Network

ERROR COUNTERS FOR TRIBUTARY SEVEN (AT THE CONTROL STATION)
DATA ERRORS OUTBOUND = 0
DATA ERRORS INBOUND = 255 (IREP, IDBCC, IHBCC)
LOCAL REPLY TIMEOUTS = 40
REMOTE REPLY TIMEOUTS = 0
LOCAL BUFFER ERRORS = 0
REMOTE BUFFER ERRORS = 0
SELECTION TIMEOUTS = 50 (IRTS)
DATA MESSAGES TRANSMITTED = 420
DATA MESSAGES RECEIVED = 310
SELECTION INTERVALS = 212
The data errors inbound counter (which is latched) indicates that NAKS have been sent:
•
•
•

For header BCC errors (IHBCC),
For data BCC errors (IDBCC), and
In response to receiving a REP (IREP).

Local reply timeouts show that REP messages have been sent to the tributary because acknowledgements for outstanding messages have not been received. Selection timeouts have also occurred where
the tributary received a poll and transmitted (raised carrier) but did not deselect itself (incomplete reply to select - IRTS). From the information gathered so far, there appears to be a problem on the link
between the tributary's transmitter and the control station's receiver. This is reenforced by the fact that
there are no data errors outbound indicating that NAKS have not been received from the tributary. The
problem could be in the control station's receiver hardware (DMVll, modem, and so forth), the cable
to the tributary, or the tributary's transmitter hardware (DMVll, modem, and so forth). The next logical step is to examine the error counters at the control station for the other tributaries. Upon doing this
the system manager notices that tributary six has the same type and relative number of errors as tributary seven. This indicates that the problem is in the control station's receiver or the cable from tributaries six and seven. (It could be that both tributaries six and seven have transmitter problems, but this
is unlikely.) Examination of the error counters for the remaining tributaries reveals very few errors.
This rules out the control station hardware.

NOTE
If failures occur at the control station, they are indicated by the fact that in most cases all stations are
affected.
The problem appears to be an intermittent cable fault on the control station's receive line (tributaries
transmit line) between tributaries five and six. (Note that this could also be a modem-related problem if
tributaries six and seven share the same modem by using a modem splitter.) More information about
the· problem can be gained by examining the error counters at the tributary end of the link.
ERROR COUNTERS FOR TRIBUTARY SEVEN (AT THE TRIBUTARY STATION)
DATA ERRORS OUTBOUND = 255 (IREP, IDBCC, IHBCC)
DATA ERRORS INBOUND = 0
LOCAL REPLY TIMEOUTS = 23
REMOTE REPLY TIMEOUTS = 40
LOCAL BUFFER ERRORS = 0
REMOTE BUFFER ERRORS = 0
SELECTION TIMEOUTS = Nj A
DATA MESSAGES TRANSMITTED = 310
DATA MESSAGES RECEIVED = 420
SELECTIONTIMEOUTS = NjA

7-15

Notice that these error counters provide the same type of information as the control station error
counters. The errors all seem to be in one direction, namely outbound. Notice also that the number of
data messages transmitted and received match those at the control station. Since data transfer is occurring, the likelihood of a hard error in the hardware is low.
NOTE
Hard errors at the control or tributary stations generally are revealed during the start-up sequence.
Examination of the remainder of the tributary's error counters reveals that tributary six has errors similar to tributary seven, and the other tributaries have very few errors. The "sluggishness" of the network
is due to the:
•

Timeouts that intermittently occur when polling tributaries six and seven, and

•

Numerous retransmissions that occur in order to get the data transferred.

These timeouts and retransmissions of data are the result of a cable fault between tributary five and six
as indicated in Figure 7-4.
7.4 MAINTENANCE
For maintenance purposes the DMVII may be operated in two basic modes:
1.
2.

Maintenance mode, or
Standard operating mode.

7.4.1 Maintenance Mode
Maintenance mode is used to t.est the DMVII by causing the microcode to respond to certain command
functions issued by a diagnostic program. Section 4.8 discusses the maintenance mode in detail.
7.4.2 Standard Operating Mode
The DMVII is tested in the standard operating mode by terminating the cable at the BC55F or BC55H
panel or at the modem end of the external cable, and running diagnostics.
The DMVII options are configured as follows:
1.

DMVII-AA (for RS-232-C; RS-423-A)
•

The modem must be disconnected and the test connector must be attached to the cable.
This may be done at the BC55H panel or at the modem end of the external cable.
EIA

Test Connector

Interface Cable

Modem Cable

RS-232-C
RS-423-A

H325
H325I

BC55H
BC55H

BC05D-25
BC55D-33

•

The clock signal is looped back in the test connector to simulate modem transmit and
receive clocks. The data rate for this application must not exceed 19.2K b/s. .

•

Modem control signals are tested for proper level conversion and cable paths. These
signals are looped back in the test connector as shown in the signal flow of Figure 2-8
View E.

7-16

DMVII-AB (CCITT V.35/DDS)
•

The modem must be disconnected and the H3250 test connector must be attached to
the BC05Z-25 cable.

•

The clock signal is looped back in H3250 to simulate modem transmit and receive
clocks.

•

Modem control signals are tested for proper level conversion and cable paths. These
signals are looped in the H3250 as shown in the signal flow of Figure 2-8 View B.

DMVII-AC (for integral modem local use)
•

The local link connections of the BC55F connector panel are disconnected at the local
panel, and the FDX switch on the BC55F connector panel is switched to half-duplex to
accomplish the external loop back.
CAUTION
If DMVll is connected to another running DMVll,
disconnect the cable at the BC55F connector panel
during diagnostic execution.

•

The data is looped back through the BC55F connector panel to test, transmit, and receive data. The data rate for this application must be 56K b/s.

7.5 PREVENTIVE MAINTENANCE (PM)
There is no specific DMVII PM schedule. A general check of voltages and connections should be done
when system PM is performed. After handling DMVII modules or cables, a complete checkout of the
device, by running all diagnostics and, if possible, the interprocessor test, is required.

7.6 CORRECTIVE MAINTENANCE
Since the FRU is either a module or cable, all corrective diagnosis should be directed towards isolating
the failing FRU. DMVII diagnostics are designed to aid in the isolation process and should be run
starting with the DMVII static logic test and continuing to the DEC/XII program. The proper sequence of diagnostics is shown in Table 7-1.

7.6.1 DMVll Static Logic Tests Parts 1 and 2
These diagnostics test the DMVJ I microcontroller circuits except for the USYRT. Through dialogue
with the operator and by using the diagnostic supervisor (DS), the program allows modification of device parameters" such as the LSI-II bus address, vector address, and processor type.
These programs are compatible with the stand-alone diagnostic supervisor and do not exceed 16K of
memory. The total time required to run DMVII static tests is approximately from 30 seconds to 2
minutes per pass, depending on the CPU type.
DMVII static logic tests part I and part 2 are compatible with XXDP+, ACT/SLIDE, and APT.
XXDP+ and ACT/SLIDE may be run in dump or chain modes. APT can be run in program or script
modes. A summary of the tests performed are listed in Tables 7-2 and 7-3.

7-17

Table 7-1

DMVll Diagnostics

Diagnostic

Description

(C)VDMA**
(C)VDMB**
(C)VDMC**
(C)VDMD**
(C)VDME**
(C)ZDMT**
(C)ZCLM**
(C)XDMD**
(C)XDME**

DMVII static logic test part 1
D MV 11 static logic test part 2
DMVl1 static logic test part 3
DMVII static logic test part 4
D MV 11 static logic test part 5
DMVII functional diagnostic
DMVl1 DCLT program
DMVII DEC/XII master module
DMVII DEC/XII slave module

Indicates the revision level

Table 7-2

DMVll Static Logic Test Part 1 Diagnostic Summary

Test Number

Description

DMVl1 availability
Master clear, run microdiagnostics
CSR addressing
CSR registers data read/write
Basic master clear
Bus reset
CSR, maintenance microcode interaction
Run flip-flop
Low RAM (OO-OF) scratch pad
Data RAM moving inversions (LOC's 0018-01FF hex)
VIA register addressing
VIA's DDRB data read/write
VIA's DDRA data read/write
VIA's ORB data read/write
VIA's timer #1 data read/write
VIA's shift register data read/write
VIA's ACR data read/write
VIA's peR data read/write
VIA's IER data read/write
VIA's ORB/DDRB master clear test
VIA's DDRB master clear test
VIA's DDRA master clear test
VIA's shift register master clear test
VIA's ACR master clear test
VIA's PCR master clear test
VIA's IER master clear test

3
4

5
6
7
8
9

10
11

12
13
14
15
16
17
18
19
20

21
22
23
24
25

7-18

Table 7-3

DMVll Static Logic Test Part 2 Diagnostic Summary

Test Number

Description

VIA timer 2 one shot mode
VIA's SR input (MODE 2) - system clock mode
NPR control register - master clear
NPR data-out
NPR data-in
NPR XFFR abort
NPR extended address bit test
Special MFG extended bit test
Q-Bus interrupt "A" & "B" selection
Bus reset with disable init set
Master clear with disable init spt
DCOK H La bit
Halt mode verification

2
3
4
5
6

7
8
9
10
11

12
13

7.6.2 DMVll Static Logic Tests Parts 3, 4, and 5
These diagnostics perform static tests of USYRT read/write logic; basic transmitter functions; receiver
sequencing and data buffering; and static operations in character and bit-stuffing modes. In addition,
data messages are sent at TTL level or through an external test connector with a specific modem interface selected.
Static logic tests provide troubleshooting capabilities such as tight-scope loops, switch options, and the
ability to lock on intermittent errors. Additional tests provide fault isolation to facilitate replacement of
the smallest field replaceable unit.
These programs conform to the stand-alone version of the diagnostic supervisor and are compatible with
ACT, APT, XXDP+, and SLIDE. Through dialogue with the operator, the programs permit modifications of device parameters such as the LSI-II bus address, vector addresses, and device priority. The
operator can specify particular tests to be run and a variety of looping, running, and reporting modes.
Device errors are reported as they occur. The report includes the test number and error description,
good and bad test data, and applicable device register contents.
A summary of the tests performed are listed in Tables 7-4, 7-5, and 7-6. For greater detail, refer to the
diagnostics listings.

Table 7-4

DMVll Static Logic Test Part 3 Diagnostic Summary

Test Number

Description

TBMT microcode interrupt test
Switch setting test
USYRT master clear test
USYRT program reset test
USYRT register addressing test
R/W bit test of PCSAR high point

2
3
4
5
6

7-19

Table 7-4 DMVll Static Logic Test Part 3 Diagnostic Summary (Cont)
Test Number

Description

7
8

R/W bit test of S / AR register
R/W bit test of PCR register
R/W bit test of TDSR register's high byte
R/W bit test of TXDB register
Pseudo R/W bit test of RXDB
Pseudo R/W bit test of RDSR's high byte
Null clock test
BCP TX reset w/IDLE = 0
BCP TX reset w/IDLE = 1
BCP TX underrun w/TSOM termination
BCP TX underrun w/RESET termination
BCP TX disable test
FIFO stacking characters test
BCP character length test
BOP TX TABORT/(IDLE = 0) test
BOP TX TABORT/(IDLE = 1) test
BOP TX TXGA (transmit go-ahead) test
BOP TX message without CRC
BOP RX character length test
TX "spacing sequence"
FIFO overrun integrity test
BCP PX overrun set and clear test
BCP RX sync-character recognition
BCP RX strip-sync test
BCP RX lost RXE test

9
10
11

12
13
14
15
16
17
18
19

20
21
22
23

24
25

26
27
28
29
30
31

Table 7-5

DMVll Static Logic Test Part 4 Diagnostic Summary

Test Number

Description

1
2
3
4
5

VRC parity generation test
VRC error detection test
BCP CRC generation/detection test
BOP RX basic receive/flag recognition test
BOP RX secondary station addressing
BOP RX all parties address test
BOP RX bit stuffing test
BOP RX underrun idle aborts/flags
BOP RX lost RXE test
BOP RX GA (go-ahead) recognition
BOP RX "ABC" test

7
8
9
10
11

7-20

Table 7-6

DMVll Static Logic Test Part 5 Diagnostic Summary

Test Number

Description

RX data flushing test
Integral modem interface test
Data test - BCP externalloopback (XLB) CRC-I6
Data test - BCP XLB odd VRC
Data test - BCP XLB even VRC
Data test - BOP XLB CRC-CCITT-I
Data test - BOP XLB CRC-CCITT-O
Modem control signal loop back test
DDCMP message test

2
3
4
5
6
7
8
9

7.6.3 DMVll Functional Diagnostic
This diagnostic performs testing on the DMVII option in a functional manner to verify its proper operation under microcode controlled use of the DDCMP. This includes a ROM CRC/CCITT check, microdiagnostic, command utilization, and error generation.
This functional test provides troubleshooting capabilities such as tight-scope loops, switch options, and
the ability to lock on intermittent errors. Additionally, this program conforms to the stand-alone version
of the diagnostic supervisor and is compatible with APT, ACT, XXDP+, and SLIDE.
Through dialogue with the operator, the program permits modification of device parameters such as the
LSI-II bus address, vector addresses, and device priority. The operator can specify particular tests to
be run and a variety of looping, running, and reporting modes.
A summary of the tests performed are listed in Table 7-7. For greater detail, refer to the diagnostics
listings.

7.6.4 DMVll Microdiagnostic Error Reporting
Internal diagnostics test registers and data paths that are internal to the microprocessor. These diagnostic routines run automatically on a master clear and must complete successfully before normal interaction with the CPU can take place.
The user program is notified of the results by way of the CSRs. Table 7-8 is a summary of the possible
results.

7.6.5 Data Communications Link Test Program (DCLT)
DCLT is a communications equipment maintenance tool designed to verify DMVII to DMVII communication links. The DCLT program provides the coverage necessary to isolate the following faults:
•
•
•
•

Communications interface program functionality,
Communication modem,
Communication cabling and installation, and
Physical link/network.

7-21

DCLT programs allow testing between modes with different hardware interfaces implementing the
same or compatible protocol. The DCLT program can be exercised under normal maintenance loopback tests:
•

Internal TTL loopback,

•

Hardware loopbacks:
Module test connectors, or
Cable test connectors,

•

Manual-controlled local modem analog and digitalloopback functions (full-duplex mode),

•

Programmable-controlled local modem analog loopback (full-duplex mode),

•

Programmable-controlled remote modem digital loop back (full-duplex mode).

DCLT's main goal is to test the communications link. DCLT assumes that the CPUs and DMVlls at
each end of the link have previously been tested and found to be in proper working order.
Prior to analyzing any data, the user must have a thorough understanding of the protocol formats applicable to the system under test.
DCLT may be used to access DMVII error counters or other information by using the print command.
The print command invokes a DCLT level called REPORT within which the following commands are
available.

Command

Description

HELP OR?

Prints help information for RPT.

TSS NNN/SW

Shows tributary status slot information where NNN is the decimal tributary address and SW is one of the following switches.

ERROR

Indicates that only error slots are to be printed.

FULL

Indicates that all tributary status slots are to be printed.

OFFSET = NN

Indicates that the tributary status slot whose offset is NN is to be printed.

GSS/SW

Print the global status information.
Switches are the same as for TSS.

LOG

Dumps the event log.

EXIT

Exits back to the command level that the user entered from. [DCLT> or
DP>].

DCLT is XXDP + or APT compatible and runs under control of the diagnostic supervisor (DS). It
requires 24K of memory. For more information on DCLT refer to the (C)ZCLM** document.

7-22

Table 7-7

DMVll Functional Diagnostic Summary

Test Number

Description

Address test
DMP ROM verification tests
DMV ROM verification tests
Initialization test
D MP interface diagnostics
RD I remains set test
Test for RDO setting
Check for procedure ,error 100
Check for procedure error 104
Test mode change of duplex portion of mode
Test for max tribs to be established
Read/write tributary status slots test
Tests for procedure error 132
Test for read/clear command
Tests for global status slots
Halt trib command tests
Kill trib command tests
Check for procedure error of 102
Check for procedure error of 110
Check for procedure error of 120
Check for procedure error of 134
Latch/unlatch poll check
Short message sending test
Check for procedure error 122
Check for procedure error 124
Check for procedure error 126
Check for procedure error 130
Transmit/receive 256 bytes, MTP, DDCMP
DMV Q22 mode TX/RX 256 bytes, MTP, DDCMP
Transmit/receive 255 bytes, MTP, DDCMP
DMP read/write modem register tests
Test of mem extension bits
Test for TX/RX 257 byte
Test for TX/RX 1 byte
Polling state tests

2..7
8-9
10
11

12
13
14
15
16
17
18
19-20
21

22
23
24
25
26
27

28
29
30
31
32
33
34
35
36
37
38
39-41
42
43
44

7-23

Table 7-8

Microdiagnostic Error Codes

BSEL6

BSEL4

Description

101

NjA

Branch test has failed and the microcode is spinning in a loop.

102

NjA

6502 internal register test has failed and the microcode is spinning in a loop.

103

NjA

Load and store instructions test has failed and the microcode is spinning in a
loop.

104

NjA

Compare instructions test has failed and the microcode is spinning in a loop.

105

NjA

Increment and decrement instructions test has failed and the microcode is spinning in a loop.

106

NjA

Shift and rotate instructions test has failed and the microcode is spinning in a
loop.

107

NjA

Logic instructions test has failed and the microcode is spinning in a loop.

110

NjA

Add with carry, subtract with carry, set and clear decimal mode instructions
test has failed and the microcode is spinning in a loop.

111

NjA

Stack push and pull instructions test has failed and the microcode is spinning in
a loop.

112

NjA

Subroutine instructions test has failed and the microcode is spinning in a loop.

113

NjA

Ram scratchpad, CSR, and NPR address resisters addressing test has failed
and the microcode is spinning in a loop.

114

N/A

Ram scratchpad,' CSR, and NPR address resisters data test has failed and the
microcode is spinning in a loop.

115

NjA

True interrupt test has failed and the microcode is spinning in a loop.

116

NjA

Ram data and addressing test has failed and the microcode is spinning in a loop.

117

N/A

Ram alternating data test has failed and the microcode is spinning in a loop.

120

NjA

Indexed indirect addressing mode instruction test has failed and the microcode
is spinning in a loop.

121

NjA

Line unit message test has failed and the microcode is spinning in a loop.

305

The microdiagnostics have completed without errors.

7-24

7.6.6 DEC/XII DMVll Modules
There are two DEC/XII modules for the DMVll; DMD* and DME*. Together these two modules
can operate:
•

Up to 16 DMVII devices in point-to-point links.

•

A single DMVII configured as a multipoint control station communicating with up to 12
tributaries.

•

Up to 16 devices configured as multipoint tributaries on the same LSI-II bus.

These modules transmit, receive, and check 32 data messages of 1024 bytes each on a given physical
link. By default, this involves a single LSI-II system with one or more devices operating in internal or
external loopback mode. However, by operator selection of nondefault modes, actual point-to-point or
multipoint operation is possible.
7.6.6.1 DMD* - DMD* is the master module. It can operate up to 16 DMVII devices in looped-back
and point-to-point modes, or a single device in multipoint control mode. DMD* can be self-sufficient or
it can communicate with slave modules on the same or another processor.
A separate DMD* module is required for each group of looped-back DMVII devices, each control
station, or each group of point-to-point devices.
The actual operating mode for each DMD* module is selected by software switch registers for that
module. The DMD* module uses switch registers SRI-SR4 as follows:
SR4 has three allowable values: 0, 1, or 2.
SR4=0 :IF TESTING DMPII
SR4= 1 :IF TESTING DMVII
SR4=2 :IF TESTING DMVII (AND Q22 SOFTWARE MODE IS DESIRED).
SR 1 has three allowable values; 0, 1, or 2.
When SRI =0:
•

All selected DMVlls run in point-to-point full-duplex mode with internal or external loopback on all devices.

•

SR2 has the following meaning:
If SR2 = 0, internal loopback is provided by the program. This is accomplished using TTLlevelloopback on the line unit. SR2=0 is the default mode of operation.
If SR2 = 1, external loopback is provided by H3254 or H3255 test connnectors on each device.
If SR2 = 2, cable loopback is provided by H3250 or H325I test connectors.

When SRl=l:
•

All selected DMVIIs run in point-to-point full- or half-duplex mode without loopback.

•

The DMD* module communicates with DME* (slave) modules on the same or other LSI-II
systems.

7-25

•

SR2 and SR3 software switch registers are not used.

When SRI =2:
•

Only one DMVII is selected.

•

The selected DMVII runs in multipoint control full- or half-duplex mode without loopback.

•

The DMD* module communicates with DME* (slave) modules on the same or other LSI-II
systems.

•

SR2 = The total number of tributaries on this multipoint link. The allowable range is from 1
to 148.

•

SR3 = The starting tributary address. The program uses this starting address to compute the
other addresses. The allowable address range is from 1 to 3778 and they may wraparound
(377 .to 1) if necessary.

7.6.6.2 DME* - DME* is the slave module. It can operate up to 16 DMVII devices in point-to-point
slave or multipoint tributary modes.
A separate DME* module is required for each group of point-to-point slaves or multipoint tributaries
on a system.
As with the DMD* module, the actual operating mode for each DME* module is selected by software
switch registers for that module. The DME* module uses software switch registers SRI-SR4 as follows:
SR4 has three allowable values: 0, 1, or 2.
SR4=0 :IF TESTING DMPll
SR4= 1 :IF TESTING DMVII
SR4=2 :IF TESTING DMVII (AND Q22 SOFTWARE MODE IS DESIRED).
SR 1 has two allowable values; 0 and 1.
When SRl=O:
•

All selected DMVII devices run in point-to-point slave, full- or half-duplex mode without
loopback.

•

The DME* module communicates with the DMD* (master) modules on the same or other
LSI-II systems.

•

SR2 and SR3 are unused.

When SRl=l:
•

All selected DMVII devices run in multipoint tributary full- or half-duplex mode without
loopback.

•

The DME* module communicates with a DMD* (master) module on the same or other LSI11 systems.

7-26

•

SR2 = The total number of tributaries on the multipoint link on this CPU. The allowable
range is from 1 to 148.

•

NOTE
If the DMVll DEC/XII modules are configured to
run in linkmode, it is recommended that the exerciser be started in run lock mode. If this is not done, the
exerciser may hang.

7.6.7 Soft Error Reports Under DEC/XII
Soft errors indicate errors which occurred causing a message' retransmission. The DMD* module
requests data errors inbound and outbound for each pass. If any errors are present, they are reported as
soft errors. The soft error report may be used in the isolation of certain DMV11 failures from UNIBUS
loading or data late problems.
The DMV11 has no data late bit or capabilities for detecting the fact that it did not obtain bus mastership in time to service the synchronous line. The DMV11 interprets such a condition as an error in the
synchronous data stream (a BCC error, transmitter underrun, or receiver overrun) and DDCMP causes
the message to be retransmitted. This occurrence causes incrementation of the cumulative error
counters in D MV 11 RAM memory.
A process of elimination must be used to determine whether soft errors (BCC) are caused by bus la-.
tency or failing DMV11 hardware.
Typically, the DMV11 should show no errors when running in a local loop back mode. This is normally a
noise-free circuit. Therefore, any soft error reports should be examined and the cause isolated.
If soft errors are reported while running a DMV11 on a fully loaded system (other devices being exercised simultaneously), they may be due to bus latency. This may be verified by running only the
DMD*DEC/X11 module with only one DMV11 enabled. If the soft errors cease, a latency condition is
indicated.
If soft errors persist while running only the DMD*DEC/X11 module, the DMV11 device diagnostics
should be run. The problem could be a faulty DMV11 or cable.

SRI and SR2 (bit 0) may be used in the isolation process. If SRI =0 and SR2= 1, DEC/XII does not
set line unit loopback but it uses an external turnaround. By running with SRI =0 and SR2=0, a TTL
loopback is performed, eliminating the possibility of the cable/turnaround connector being faulty.
TTL loopback eliminates the level converters and the integral modem. The bit rate selected is 56K b/s
using the internal clock.

7-27

APPENDIX A
DDCMP IN A NUTSHELL

A.I DDCMP
The Digital Data Communications Message Protocol (DDCMP) provides a data link control procedure
that ensures a reliable data communication path between communication devices connected by data
links. DDCMP has been designed to operate over full- and half-duplex synchronous and asynchronous
channels in both point-to-point and multipoint modes. It can be used in a variety of applications such as
distributed computer networks, host front-end processors, remote terminal concentrators, and remote
job entry-exit systems.
A.I.I Controlling Data Transfers
The DDCMP message format is shown in Figure A-I. Three control characters are provided in
DDCMP to differentiate between the three possible types of messages:
•
•
•

SOH - Data message follows,
EN Q - Control message follows,
D LE - Maintenance message follows.

Note that the use of a fixed-length header and message size declaration obviates the requirement for
extensive message and header delimiter codes.

SOH

DATA
CRC-2
COUNT FLAG RESPONSE SEQUENCE ADDRESS CRC-1
(ANY NUMBER OF 8-BIT
8 BITS
16 BITS
8 BITS
16 BITS
14 BITS 2 BITS 8 BITS
CHARACTERS UP TO 214)

MK·2248

Figure A-I

DDCMP Data Message Format

A.1.2 Error Checking and Recovery
DDCMP uses a 16-bit cycle redundancy check (CRC-16) for detecting transmission errors. When an
error occurs, DDCMP sends a separate negative acknowledge (NAK) message. DDCMP does not require an acknowledgement message for all data messages. The number in the response field of a normal
header or in either the special NAK or acknowledge (ACK) control message specifies the sequence
number of the last good message received. For example, if messages 4, 5, and 6 have been received
since the last time an acknowledgement was sent and message 6 is bad, the NAK message specifies
number 5 which says "messages 4 and 5 are good and 6 is bad." When DDCMP operates in full-duplex
mode, the line does not have to be turned around; the NAK is simply added to the sequence of messages
for the transmitter.
When a sequence error occurs in DDCMP, the receiving station does not respond to the message. The
transmitting station detects, from the response field of the messages it receives (or via timeout), that

A-I

the receiving station is still looking for a certain message and sends it again. For example, if the next
message the receiver expects to receive is 5, but receives 6 instead, the receiver does not change the
response field (which contains a 4) of its data messages. The receiver will say, "I accept all messages up
through message 4 and I'm still looking for message 5."

A.t.3 Character Coding
DDCMP uses ASCII control characters for SYN, SOH, ENQ and DLE. The remainder of the mes'
sage, including the header, is transparent.
A.t.4 Data Transparency
DDCMP defines transparency by use of a count field in the header. The header is of a fixed length. The
count in the header determines the length of the transparent information field, which can be from 1 to
16,383 bytes long. To validate the header and count field, it is followed by a CRC-16 field; all header
characters are included in the CRC calculation. Once validated, the count is u~ed to receive the data
and to locate. the second CRC-16, which is calculated on the data field. Thus, character stuffing is
avoided.

A.I.S Data Channel Utilization
DDCMP uses either full-duplex or half-duplex circuits at optimum efficiency. In the full-duplex mode,
DDCMP operates as two independent one-way channels, each containing its own data stream. The only
dependency is the acknowledgements which must, be sent in the data stream in the opposite direction.
Separate ACK messages are unnecessary, therefore, reducing the control overhead. Acknowledgements
are simply placed in the response field of the next data message for the opposite direction. If several
data messages are received correctly before the terminal is able to send a message, all of them can be
acknowledged by one response. Only when a transmission error occurs, or when traffic in the opposite
direction is light (no data message to send), is it necessary to send a special NAK or ACK message,
respectively.
.
In summary, DDCMP data channel utilization features include:
1.

The ability to run on full-duplex or half-duplex data channel facilities,

Low control character overhead,

No character stuffing,

No separate ACKs when traffi'c is heavy; this saves on extra sync-characters and intermessage gaps,

Multiple acknowledgements (up to 255) with one ACK, and

The ability to support point-to-point and multipoint lines.

A.2 PROTOCOLDESCRIPTION
DDCMP is a very general protocol; it can be used on synchronous or asynchronous, half-duplex or fullduplex, serial or parallel, and point-to-point or multipoint systems. Most applications involving protocols
are half-duplex or full-duplex transmissions in a serial synchronous mode; that operating environment is
emphasized in the following description.
The header is the most important part of the message because it contains the message sequence numbering information and the character count, the two most important features of DDCMP. Because of
the importance of the header information, it merits its own CRC blockcheck, indicated in Figure A-2 as
CRC-I. Messages that contain data, rather than just control information, have a second section which
contains any number of 8-hit characters (up to a maximum of 16,383) and a second CRC (indicated in
Figure A-2 as CRC-2).

NOTE 1
~

RESPONSE SEQUENCE ADDRESS
COUNT FLAG
CLASS
14 BITS 2 BITS
a BITS
a BITS
a BITS

xxxxxxxx
SOH-DATA MESSAGES

10000001
00000101
ENQ {ACKNOWLEDGEMENT
NEGATIVE ACKNOWLEDGE 00000101

REASONS:

ENQ
OLE

XXXXXXXXXXXXXX
CHARACTER COUNT
00000001000000
00000010---------

BCC HEADER ERROR
BCC DATA ERROR
REP RESPONSE
BUFFER UNAVAILABLE
RECEIVER OVERRUN
MESSAGE TOO LONG
HEADER FORMAT ERROR

REPLY MESSAGE
START MESSAGE
START ACKNOWLEDGEMENT
MAINTENANCE MESSAGE

00000101
00000101
00000101
10010000

xx
QS
QS
QS

CRC 1
16 BITS

INFORMATION
ANY NUMBER CRC 2
OF a-BIT
16 BITS
CHARACTERS

XXXXXXXX
RESP #
RESP #
RESP #

XXXXXXXX
MESSAGE#
00000000
00000000

XXXXXXXX
ADDRESS
ADDRESS
ADDRESS

00000000
00000000
00000000
00000000

LSTMESS#
00000000
00000000
00000000

ADDRESS
ADDRESS
ADDRESS
ADDRESS

000001
000010
000011
001000
001001
010000
010001

00000011000000
00000110000000
00000111000000
CHARACTER COUNT

QS
11
11
11

NOTES:
1. ONLY THE DATA MESSAGE AND THE MAINTENANCE MESSAGE HAVE CHARACTER COUNTS, SO
ONLY THESE MESSAGES HAVE THE INFORMATION AND CRC2 FIELDS SHOWN IN THE MESSAGE
FORMAT DIAGRAM ABOVE.
2. "RESP #" REFERS TO RESPONSE NUMBER. THIS IS THE NUMBER OF THE LAST MESSAGE
RECEIVED CORRECTLY. WHEN USED IN A NEGATIVE ACKNOWLEDGE MESSAGE, IT IS ASSUMED
THAT THE NEXT HIGHER NUMBERED MESSAGE WAS NOT RECEIVED, WAS RECEIVED WITH
ERRORS, OR WAS UNACCEPTED FOR SOME OTHER REASON. SEE "REASONS."
3. "MESSAGE#" IS THE SEQUENTIALLY ASSIGNED NUMBER OF THIS MESSAGE. NUMBERS ARE
ASSIGNED BY THE TRANSMITTING STATION MODULO 256; I.E., MESSAGE 000 FOLLOWS 255.
4. "LSTMESS#" IS THE NUMBER OF THE LAST MESSAGE TRANSMITTED BY THE STATION. SEE THE
TEXT DISCUSSION OF REP MESSAGES.
5. " ADDRESS" IS THE ADDRESS OF THE TRIBUTARY STATION IN MULTIPOINT SYSTEMS AND IS
USED IN MESSAGES BOTH TO AND FROM THE TRIBUTARY. IN POINT TO POINT OPERATION, A
STATION SENDS THE ADDRESS "1" BUT IGNORES THE ADDRESS FIELD ON RECEPTION.
6. "Q" AND "s" REFER TO THE QUICK SYNC FLAG BIT AND THE SELECT BIT. SEE TEXT.
MK·2249

Figure A-2

DDCMP Message Format in Detail

A-3

Before the 'message format is discussed in greater detail, the message sequencing system should be explained because most of the header information is directly or indirectly related to the sequencing operation.
In OOCMP, any pair of stations that exchange messages with each other number those messages sequentially starting with message number one. Each successive data message is numbered using the next
number in sequence, modulo 256. Thus, a long sequence of messages would be numbered 1, 2, 3, ... 254,
255, 0, 1, ... 255. The first message sequence always starts with a number 1, and every sequence thereafter begins with a O. The numbering applies to each direction separately. For example, station A might
be sending its messages 6, 7, and 8 to station B, while station B is sending its messages 5, 6, and 7 to
station A. Thus, in a multipoint configuration where a control station is engaged in two-way communication with ten tributary stations, there are 20 different message number sequences involved - one
sequence for messages from each of the ten tributaries to the control station, and one sequence for
messages from the control station to each of the ten tributaries.
Whenever a station transmits a message to another station, it assigns its next sequential message number to that message and places that number in the sequence field of the message header. In addition to
maintaining a counter for the sequentially numbered messages which it sends, the station also maintains
a counter of the message numbers received from the other station. It updates that counter whenever a
message is received with a message number exactly one higher than the previously received message
number. The contents of the received message counter are included in the response field of the message
being sent, to indicate to the other station the highest sequenced message that has been received.
When a station receives a message containing an error, that station sends a negative acknowledge
(NAK) message back to the transmitting station. OOCMP does not require an acknowledgement for
each message, as the number in the response field of a normal header (or in either the special NAK or
positive acknowledgement message ACK) specifies the sequence number of the last good message received.
When a station receives a message that is out of sequence, it does not respond to that message. The
transmitting station detects this from the response field of the messages which it receives; if the reply
interval expires before the transmitting station receives an acknowledgement, the transmitting station
sends a REP (reply) message. The REP message contains the sequence number of the most recent
unacknowledged message sent to the remote station. If the receiving station has correctly received the
message referred to in the REP message (as well as the messages preceding it), it replies to the REP by
sending an ACK. If it has not received the message referred to in sequence, it sends a NAK containing
the number of the last message that it did receive correctly. The transmitting station then retransmits
all data messages after the message specified in the NAK.
The numbering system for OOCMP messages permits up to 255 unacknowledged messages outstanding; a useful feature when working on high-delay circuits such as those using satellites. However,
the DMV11 limits the maximum number of unacknowledged messages outstanding to be 127.

A.3 MESSAGE FORMAT
With the above background, it is now time to explore the various OOCMP message formats in full
detail, as shown in Figure A-2. The first character of the message is the class of message indicator,
represented in ASCII with even parity. There are three classes of messages; data, control, and maintenance. These are indicated by class of message indicators SOH, ENQ, and OLE, respectively. The next
two characters of the m.essage are broken into a 14-bit field and a 2-bit field. The 14-bit field is used in
data and maintenance messages to indicate the number of characters that follow the header CRC field
and form the information part of the message. In control messages, the first eight bits of the 14-bit field
are used to designate what type of control message it is; the last six bits are generally filled with zeros.
The exception is in NAK messages where the last six bits are used to specify the reason for the NAK.
The 2-bit field contains the quick-sync and· select flags.

A-4

The quick-sync flag is used to inform the receiving station that the message will be followed by synccharacters; the receiver may wish to set its associated synchronous receiver hardware into sync-search
mode and sync-strip mode. This reestablishes synchronization and syncs are discarded until the first
character of the next message arrives. The purpose of this is to permit the receiving station to engage
any hardware sync-stripping logic it might have and prevent it from filling its buffers with sync-characters. The select flag is used to control link management in half-duplex or multipoint configurations
where transmitters need to get turned on and off.
Link management is the process of controlling the transmission and reception of data on links where
there may be two or more transmitters and/or receivers actively connected to the same signal channels.
This is true of half-duplex point-to-point links, as well as full- and half-duplex multipoint links. On halfduplex links, only one transmitter may be active at a time; on full-duplex links, only one slave transmitter may be active on the link at a time.
A station on such a link may transmit when it has been selected or granted ownership of the link. This
ownership is passed by use of the select flag existing in all messages. A select flag set in a received
message allows the addressed station to transmit after completing reception of the message. The select
flag also means that the transmitter ceases transmitting after the message is sent.
The response fiel'd contains the number of the last message correctly received. This field is used in data
messages and in the positive and negative acknowledge types of control messages. Its function should be
evident from the preceding discussion of sequence control.
The sequence field is used in data messages and in the REP type of control message. In a data message,
it contains the sequence number of the message as assigned by the transmitting station. In a REP message, it is used as part of the question, "Have you received all messages up through message number
(specify) correctly?"
The address field is used to identify the tributary station in multipoint networks and is used in messages
both to and from the tributary. In point-to-point operation, each station uses an address of 1.
In addition to the positive and negative acknowledgement and REP types of control messages, there are
also start and start acknowledge control messages. These are used to place the station which receives
them in a known state. In particular, they initialize the message counters, timers, and other counters.
The start acknowledge message indicates that this has been accomplished.
Figure A-2 also shows the maintenance message. This is typically a bootstrap message containing load
programs in the information field. A complete treatment of maintenance messages and start-up procedures is beyond the scope of this book.

NOTE
Refer to the DDCMP specification order (AADS99A-TC) for a complete detailed description of
DDCMP.

A-5

APPENDIX B
FLOATING DEVICE
AND VECTOR ADDRESSES

B.l FLOATING DEVICE ADDRESSES
UNIBUS and LSI-II addresses, starting at 760010 and continuing through 763776, are designated as
floating device addresses (see Figure B-1). These are used as register addresses for communications
(and other) devices interfacing with the PDP-II (refer to Table B-1).

NOTE
Some devices are not supported by LSI· 11; however,
the same scheme applies. That is, gaps are provided
as appropriate. The convention for assigning these
addresses is as follows:

A gap of 108 must be left between the last address of one device type and the first address of the next
device type. The first address of the next device type must start on a modulo 108 boundary. The gap of
108 must also be left for devices that are not installed but are skipped over in the priority ranking list.
Multiple devices of the same type must be assigned contiguous addresses. Reassignment of device types
already in the system may be required to make room for additional ones.
B.2 FLOATING VECTOR ADDRESSES
Vector addresses, starting at 300 and proceeding upward to 777, are designated as floating vectors.
These are used for communications (and other) devices that interface with the PDP-II and VAX-II.
Multiple devices of the same type would be assigned vectors sequentially (refer to Table B-2).
NOTE
Some devices are not supported by LSI-tt; however,
the same scheme applies. Vector size is determined
by the device type.

There are no gaps in floating vectors unless required by physical hardware restrictions (in data communications devices, the receive vector must be on a zero boundary and the transmit vector must be on a
48 boundary).

B-1

777 777
DIGITAL EQUIPMENT
CORPORATION

2K
WORDS

(FIXED ADDRESSES)

770000
767 777

DR11-C

1K
WORDS

t
USER ADDRESSES

764000
763 777

t
1K
WORDS

FLOATING ADDRESSES
DIGITAL EQUIP CORP (DIAGNOSTICS)

760010
760006
760000
757 777

001 000
000777

VECTORS

FLOATING VECTORS

000300
000277
TRAP & INTERRUPT
VECTORS

48
VECTORS
~

____________________

000000

MK-2190

Figure B-1

UNIBUS and LSI-ll Address Map

B-2

Table B-1

Floating CSR Address Devices

Rank

Option

Decimal
Size

Octal
Modulus

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24

DJll
DHll
DQll
DUll
DUPll
LKIIA
DMClljDMRll
DZII * and DZVlljDZ32
KMCll
LPP11
VMV21
VMV31
DWR70
RLl1 and RLVl1
LPAII-K
KWII-C
Reserved
RX11
DRI1-W
DRll-B
DMPII-AD
DPV11
ISB11
DMVII-AD

4
8
4
4
4
4
4
4
4
4
4
8
4
4
8
4
4
4
4
4
4
4
4
8

10
20t
10
10
10
10
10
10
10
10
10
20t
10
10 (extra only)
20 (extra only)
10
10
10 (extra only)
10
10 (after second)
10
10
10
20

*DZIIE and DZIIF are dual OZlls and are treated by the algorithm as two DZlls.
tStarting CSR address must be an even multiple of 20 (octal).
Table B-2

Floating Interrupt Vector Devices

Rank

Option

Decimal
Size

Octal
Modulus

1
2
2
2
3
4
5
6
7
8
9

DCl1
KL II (extra)
OLI1-A (extra)
DLI1-B (extra)
DPl1
OMII-A
DNll
OMII-BB
DH II modem control
DRII-A
DRll-C

4
4
4
4
4
4
2
2
2
4
4

10
10*
10*
10
10
10
4
4
4
10*
10*

*The vector for the device of this type must always be on a 108 boundary.

B-3

Table B-2

Floating Interrupt Vector Devices (Cont)

Rank

Option

Decimal
Size

Octal
Modulus

10
11
12
13
14
14
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46

PA611 (reader & punch)
LPD11
DT11
DX11
DL11-C
DL11-D
DL11-E
DJ11
DH11
GT40jVSV11
LPS11
DQl1
KW11-W
DUll
DUP11
D V and modem control
LK11-A
DWUN
DMC11jDMRll
DZl1jDZ32jDZV11
KMC11
LPP11
VMV21
VMV31
VTVOI
DWR70
RLl1jRLV11
TS11
LPA11-K
IPll jIP300
KWII-C
RX11jRX211
DR11-W
DR11-8
DMP11-AD
DPV11
ML11
ISB11
DMVII-AD

8
4
4
4
4
4
4
4
4
8
12
4
4
4
4
6
4
4
4
4
4
4
4
4
4
4
2
2
4
2
4
2
2
2
4
4
2
4
4

10*
10
10*
10*
10*
10*
10*
10*
lOt
10
10*
lOt
10
10*
10*
10
10
10
10*
10*
10
10
10
10
10
10*
4
4 (after the first)
10
4
10
4 (after the first)
4
4 (after the first)
10
10
4 (MASSBUS device)
10
10

*The vector for the device of this type must always be on a lOs boundary.
tThese devices can have either a M7820 or M7821 interrupt control module. However, it should always
be on a 108 boundary.

B-4

B.3 EXAMPLES OF DEVICE AND VECTOR ADDRESS ASSIGNMENT
This example has three devices that require device and vector address assignment in the floating address space. The devices are:

•
•
•
Device
(Option)

RLVII

DPVII
DPVII

DMVII

I RLVII
2 DPVIIs
I DMVII
Device
Address
760010
760020
760030
760040
760050
760060
760070
760100
760110
760120
760130
760140
760150
760160
760170
760200
760210
760220
760230
760240
760250
760260
760270
760300
760310
760320
760340
760360

Vector
Address

300

310
320

330

Comment
Gap left for DJ II
Gap left for DH II
Gap left for DQ II
Gap left for DU II
Gap left for DUPII
Gap left for LK II A
Gap left for DMCII/DMRII
Gap left for DZ 11 /DZV II
Gap left for KMC II
Gap left for LPP II
Gap left for VMV21
Gap left for VMV31
Gap left for DWR 70
First and only RL V II
Gap left between RL V11 and next
device
Gap left for LPA II-K
Gap left for KW II-C
Reserved
Gap left for RX II
Gap left for DRII-W
Gap left for DRII-B
Gap left for DMPII
First DPVII
Second 0 PV II
Gap left between DPV II and next
device
Gap left for ISB II
First and only 0 MV II
Gap left after last device, in this
case the DMVII, to indicate that no
other devices follow

B-5

APPENDIX C
MODEM CONTROL REGISTER FORMATS

e.l MODEM CONTROL REGISTER FORMATS
The modem signals made available by the DMVII can be examined or modified by the user program if
needed. This supplies the flexibility needed to meet the various modem interface requirements of different countries.
READ MODEM STATUS
BSEL4:
Bit

Name

Description

CARRIER

Received line signal detector, commonly referred to as carrier detect, indicates that there is an appropriate audio tone being received from the remote modem. Typically, in full- and half-duplex applications, - carrier detect is on whenever the
communications line is intact and the remote modem has the signal request to send asserted (the modem is transmitting). This
signal is also applicable to the DMVII integral modem.

NOT USED

ALWAYS READ AS ZERO.

CLEAR TO SEND

This signal is generated by the local modem to indicate whether
or not it is ready to transmit data. Clear to send is the local
modem's response to the asserting of request to send. This signal
has a slightly different meaning with different modems. With
some modems it indicates that the carrier is being received from
the remote modem, and, therefore, is an indication that a suitable
communications channel exists.

MODEM READY

This signal indicates that the modem is ready to operate. The ON
condition indicates that the local modem is connected to the communications line and is ready to exchange further control signals
with the DMVII. The OFF condition indicates that the local
modem is not ready to operate. This signal, when implemented by
the modem, is used by the DMVll to detect either a power-off
condition or a cable-related modem malfunction.

HALF-DUPLEX

This signal, when asserted, indicates that the DMVl1 is in the
half-duplex mode. This means that the DMVll is connected to a
communications line designed for transmission in either direction, but not in both directions simultaneously. When cleared, it
implies full-duplex operation which is two-way independent transmission in both directions.
C-I

Bit

Name

Description

REQUEST TO SEND

This signal serves to control the data channel transmit function of
the local modem, and on a half-duplex channel, to control the direction of data transmission of the local modem. On a full-duplex
channel, the ON condition maintains the modem in the transmit
mode, and the OFF condition maintains the modem in the nontransmit mode. On a half-duplex channel, the ON condition
maintains the modem in the transmit mode and inhibits the receive mode. The OFF condition maintains the modem in the receive mode. A transition from OFF to ON instructs the modem to
enter the transmit mode. The modem responds by taking such action as may be necessary and indicates completion of such actions
by asserting clear to send, thereby, indicating to the DMVll that
data may be transferred across the communications channel. A
transition from ON to OFF instructs the modem to complete the
transmission of all data that was previously transferred to the
modem and then assume a nontransmit or receive mode, whichever is appropriate. The modem responds to this instruction by
turning OFF the signal clear to send when it is again prepared to
respond to a subsequent ON condition of request to send.

DATA TERMINAL
READY

This signal controls the switching of the local modem to and from
the communications line. When asserted, this signal serves to inform the local modem that the DMVll is ready to operate. This
signal also prepares the modem for connection to the communications line and maintains this connection as long as it is ON.
When turned OFF, this signal causes the local modem to disconnect after all data previously transferred to the modem has
been transmitted. This signal can be used by the local modem to
detect a power-off condition in the DMVll or a cable-related
modem malfunction.

RING

This signal indicates whether an incoming call signal is being received by the local modem. When ON, this signal indicates that
an incoming call (ringing) signal is being received by the local
modem. The ON state of ring must appear approximately at the
same time as the ON segment of the ringing cycle (during rings)
on the communications line. The OFF condition must be maintained during the OFF segment of the ringing cycle (between
rings) and at all other times that ringing is not being received.
This signal is not affected by the state of data terminal ready.

READ MODEM STATUS

BSEL5
Bit

Name

Description

MODE

This bit indicates the operational mode of the line unit. A one indicates character-oriented protocol operation, and a zero indicates bit-oriented protocol operation. The DMVll initializes
this bit to one.
C-2

Bit

Name

Description

NOT USED

ALWAYS READ AS ZERO.

TEST MODE

This signal indicates whether or not the local modem is in a test
condition. (This signal applies only to modems that support this
feature.) When in the ON condition, this signal indicates to the
DMVII that the local modem has been placed in a test condition.
The ON condition can also be in response to either local or remote activation by means of any other modem test condition. Activation of a telecommunications network test condition (for example, facility loopback) that is known to the modem can also
cause this signal to be ON. In the OFF condition, this signal indicates that the modem is not in the test mode and is available for
normal operation.

NOT USED

ALWAYS READ AS ZERO

NOT USED

ALWAYS READ AS ZERO

NOT USED

ALWAYS READ AS ZERO

NOT USED

ALWAYS READ AS ZERO

NOT USED

ALWAYS READ AS ZERO

WRITE MODEM CONTROL

BSEL4
Bit

Name

NOT USED

Description

SELECT STANDBY

Defaulted to 0 by DMVII hardware.

MAINTENANCE
MODE 2

Defaulted to 0 by DMVll hardware.

MAINTENANCE
MODEl

Defaulted to 0 by DMVII hardware.

HALF-DUPLEX

The DMVII uses this bit to place the line unit into the half-duplex mode. The user program cannot set or clear this bit. The
DMVl1 can change line characteristics only through the mode
definition command. The DMVII is equipped with a software interlock that prevents simultaneous transmission and reception
when in the half-duplex mode. While the transmitter is transmitting, the receiver is disabled from receiving data via a hardware interlock.

SELECT
FREQUENCY

This signal is used to select the transmit and receive frequency
bands of a modem. In the ON condition, the higher frequency

C-3

Bit

Description

Name

band is selected for transmission to the communications channel,
and the lower frequency band is selected for reception from the
communications channel. When OFF, the lower frequency band
is selected for transmission to the communications channel, and
the higher frequency band is selected for reception from the communications channel.

NOTE
The modem, if it supports select frequency, must be
set up to ignore this signal from DMVll.
6

DATA TERMINA~
READY

This signal controls switching of the local modem to and from the
communications line. When asserted, this signal serves to inform
the local modem that the DMVII is ready to operate. This signal
also prepares the modem for connection to the communications
line and maintains this connection as long as it is ON. When
turned OFF, this signal causes the local modem to disconnect after all data previously transferred to the modem has been transmitted. This signal can be used by the local modem to detect a
power-off condition at the DMVII or a cable-related modem
malfunction.

NEW SIGNAL

This signal determines whether or not the local modem will rapidly respond to new data onthe communications line. This signal is
used at control stations in multipoint networks where the remote
modems operate in switched-carrier mode. This incoming signal
to the control station appears as ·a series of short message bursts
transmitted by each tributary as it responds to the poll from the
control station. In order to permit rapid accommodation to signals from several tributaries appearing in quick succession, the
control station informs the local modem when a new signal- is
about to begin by asserting polling for a brief interval. For synchronous systems, clock timing on the incoming message varies
from message to message because the remote modems are in no
way synchronized to each other. If the time interval between messages is too short, the clock holdover after the end of one message
may preclude rapid synchronization on the following message.
The use of this signal allows the control station to reset the
modem receiver timing recovery circuit, enabling it to respond
more quickly to the line signal present after polling has been
turned OFF. This signal applies only to modems that support polling.

C.l RS-449 VERSUS RS-l3l-C
The most common interface standard in use during recent years is RS-232-C. However, when used in
modern communications systems it has critical limitations; the most serious being speed and distance.
For this reason, the interface standard RS-449 was developed to replace RS-232-C. This standard maintains a degree of compatibility with RS-232-C to accommodate an upward transition to RS-449.
The most significant difference between RS-449 and RS-232-C is the electrical characteristics of signals used between the data communications equipment (DCE) and the data terminal equipment
C-4

(DTE). The RS-232-C standard specifies only unbalanced circuits, whereas, RS-449 specifies both balanced and unbalanced circuits. The specifications for these two circuit types supported by RS-449 are
contained in EIA standards RS-422-A for balanced circuits and RS-423-A for unbalanced circuits.
These new standards permit greater transmission speeds and allow greater distance between the DTE
and DCE. The maximum transmission speeds supported by RS-422-A and RS-423-A specified circuits
vary with circuit length. The normal transmission speed limits are 20K bls for RS-423-A at 61 m (200
feet) and 2M bls for RS-422-A also at 61 m (200 feet). These normal transmission speeds can be varied
by tradeoffs between speed and distance.
Another major difference between RS-449 and RS-232-C is the specification of two new connectors to
accommodate the leads required to support additional circuit functions and the balanced interface circuits. One connector is a 37-pin cinch used to accommodate the majority of data communications applications. The other is a 9-pin cinch for applications requiring secondary channel functions. Some of the
new circuits implemented by RS-449 support local and remote loopback testing and standby channel
selection.
The transition from RS-232-C to RS-449 will not happen immediately. Therefore, applications that require connection between RS-232-C and RS-449 interfaces must adhere to the limitations of RS-232-C,
which specifies a normal transmission speed of 20K bls at a maximum distance of 15.2 m (50 feet).
DMVII does not support RS-422-A balanced circuits.

C-5

APPENDIX D
MODEM CONTROL
D.I MODEM CONTROL
There are two levels of modem control available to the DMV11. The first level is provided by the hardware, and the second by the DMVII microcode.
D.I.I Hardware Modem Control
The DMVII provides the following modem control function:
•

Prevention of simultaneous transmission and reception in half-duplex mode.

Half-Duplex Mode - When set, HALF-DUPLEX specifies that the DMVII is in the half-duplex mode.
In half-duplex mode, a hardware interlock prevents the DMV11 from transmitting and receiving simultaneously.
NOTE
This hardware lockout prevents the DMVII from
being used in the half-duplex mode on a full-duplex
modem with the continuous carrier option installed.
D.I.2 Modem Control Implemented by the DMVII Microcode
The modem control signals implemented by the DMVII are:
•
•
•
•
•

Modem ready (data set ready),
Request to send/clear to send,
Carrier,
Data terminal ready, and
Auto answer.

Each of these signals are outlined in Table D-1.
Once modem ready goes ON, the DMVl1 reports any transition from ON to OFF to the user program
by issuing a control response containing the code for the system-event modem disconnect. The microcode tests that modem ready is OFF for 10 ms. Transmission is initially inhibited by the microcode by
interlocking the signals modem ready and request to send.
Whenever the signal carrier detect is dropped by the modem for greater than 1.28 seconds, the user
program is notified by a control response containing the code for the system event modem carrier loss.
Diagrams are used in the discussion of modem control functions. Refer to Figure 0-1 as an aid in interpreting these diagrams. The flow depicted by the diagrams (Figures D-2 through D-8) describes the processing of EIA modem control signals by the OMVl1. Each diagram represents a serial flow for a specific modem control function. However, the functions performed, as represented by each diagram, are
performed in parallel. The readable and writeable modem signals listed on the diagram for modem status can be read and written through the control command using the request keys read modem status
and write mode control.

D-l

Table D-l

DMVll Modem Control Functions

Signal

Description

Data Set ReadyModem Ready:

Software interlock prevents the DMV II from transmitting if DSR is not
returned. If DSR drops (meaning that it once was asserted) for a period
of 10 ms, the transmitter and receiver are resynchronized, the transmitter
and receiver sections of the microcode are reset to the idle state to allow
the user to return buffers, DTR is then dropped to clear the line (see
DTR for reasserting conditions), and the user is then notified of the DSR
drop via a control-out for disconnect.
Software interlock preventing the DMVII from transmitting if DSR is
not returned: If the DMVII has been instructed by the user to start up
the communications line, and DSR is not asserted, the DMVl1 does not
transmit. There is no timer started for the first assertion of DSR. It is the
responsibility of the user to ensure that the modem is plugged in. Also, if
the modem is a dial-up modem, the user should make sure that the number is dialed. In most cases the start command is issued with the intent of
waiting for an incoming call. In this case, the timer value is arbitrary so
that it has been left up to the user software to determine this timeout. If
data terminal ready (DTR) is not asserted because of a past error condition that caused the dropping of DTR (that is, disconnect), the user program may assert DTR via the write modem command to enable transmission.

Request to Send/
Clear to Send:

For all applications: Before RTS is asserted (if already asserted this is
bypassed) CTS is checked for the "ON" condition. If CTS is '~ON", a
10-20 ms timer is started while waiting for CTS to drop. If CTS does not
drop within the timer period, constant CTS is assumed and RTS is set.
For all applications: Software interlock prevents transmission if CTS is
not returned. IF CTS is not returned within 30 seconds (plus or minus 10
ms), a disconnect control-out is queued with a CTS failure code in
BSEL 7. The transmitter and receiver are resynchronized, the transmitter
and receiver sections of the microcode are reset to the idle state to allow
the user to return buffers, and DTR is then dropped to clear the line. (See
DTR for reasserting conditions).
For all applications: During the time that RTS is set, every 10 ms CTS is
checked for the "ON" condition. If CTS stays in the "OFF" condition for
30 seconds (plus or minus 10 ms), a disconnect control out is queued with
a CTS failure code in BSEL 7. The transmitter and receiver are resynchronized, the transmitter and receiver sections of the microcode are
reset to the idle state to allow the user to return buffers, and DTR is then
dropped to clear the line. (See DTR for reasserting conditions).
For all half-duplex applications: The setting of request to send is "ANDED" with the half-duplex bit in the hardware to "blind" the receiver
when transmitting.

D-2

Table D-l

DMVll Modem Control Functions (Cont)

Signal

Description

Carrier:

Software interlocks prevent transmission in half-duplex if carrier is in the
"ON" condition. This prevents the DMVll from running half-duplex on
four-wire constant carrier modems.
For all applications: Hardware interlock of carrier and the receiver clock
stop the USYRT from receiving if carrier were to drop in the middle of a
message.
For all applications: If carrier "drops" while the DMVll is in the process
of receiving the carrier, the loss timer is started. If the carrier loss timer
expires (1.28 second interval), the user is notified via a control-out for
carrier loss. The receiver is then resynchronized and the receiver microcode is reset to the waiting state for the next message. If the carrier loss is
less than 1.28 seconds (carrier is reasserted before the timeout), the message being received is allowed to finish. If CRC errors are detected (normal case), the protocol recovers from the failure.

Data terminal ready:

DMVll clears DTR on a power-up bus initialization, and a master clear.
This is a hardware function. DTR is not gated from the interface drivers
when the DMVll is placed in loop back mode. DTR is monitored by diagnostics running in internalloopback to ensure that the microcode does not
set it.
When DTR is dropped because of errors, it is only reasserted if any of the
following conditions exist: auto answer is enabled or remote load detect is
enabled. The code is in the process of power-on boot or request boot.

Auto Answer:

This option is switch selectable. If enabled, the DMVll asserts DTR and
waits for modem ready (DSR). Because of the difference between
modems in the U.S. and other countries, ring is not used as an indication
that an incoming call has been established. As it stands, DSR is the indication that the call has been established. If a valid DDCMP message is
not received within 30 seconds (plus or minus 10 ms) after a connection is
established, DTR is dropped (hang up the phone). The connection is considered to be established on assertion of carrier or clear to send. The
transmitter and receiver are resynchronized, the transmitter and receiver
sections of the microcode are reset to the idle state, and DTR is then reasserted after DSR drops (or in 10 seconds whichever comes first). In this
case the user is not notified of the cancelled call. An internal counter is
incremented to log the incoming calls (latches at 256) and is available for
reading by the user program.

D-3

CONDITIONS TO BE SATISFIED. IF CONDITIONS ARE NOT
MET SERIAL FLOW DOES NOT CONTINUE.

ACTIONS PERFORMED BY DMV11.

C__)

ENTRY OR EXIT SYMBOLS

MK-2657

Figure D-I

Flow Diagram Symbology

D-4

POWER ON

SYSTEM
IN ITIALIZATION

[2.4]

DEVICE
MASTER CLEAR

[2.4]

-----,~--

[2.5]

POWER ON
BOOT ENABLED
(SWITCH)
USER ISSUES
MODE DEFN
COMMAND

MODE DEFINED
IN SWITCHES

BOOT
BIT SET

[2.6]

[2.2]

SET DTR
SET CALTMR
ON

SET DTR
SET CALTMR
=ON

=
[2.3]

~_---,~----l

r---------------~------------,

USER REQUEST
MODEM STATUS
READ/WRITE

CALTMR

= ON

A ~----------~----------------~
DSR = ON

[2.2]

DSR = ON
CD= ON

[2.1]
MODSTAT

SCAN FOR
REMOTE
LOAD
MESSAGE

VALID
MESSAGE

DSR = ON TO
OFF FOR
10mSEC

MESSAGE TO
BE SENT

P/MOP

= ON

P/MOP

= OFF

NOTIFY USER OF
DSR DROP
DISCONNECT
(CONTROL RESPONSE)

TRANSMIT

NOTES:
[2.1] REMOTE LOAD DETECT IS A MAINT. DDCMP MESSAGE INITIATING A DOWN LINE LOAD.
[2.2] CALTMR • (CALL TIMER): USED TO DETERMINE IF VALID MESSAGE IS RECEIVED. "ON" INDICATES TIMER
RUNNING.
[2.3] P/MOP • PRIMARY MAINTENANCE OPERATION PROTOCOL, REQUESTING REMOTE LOAD.
[2.4] RUN COMPLETE MICRODIAGNOSTICS (MICROPROCESSOR AND LINE UNIT)
[2.5] HARDWARE FUNCTION
[2.6] INVOKE PRIMARY MOP BOOT (BIT FIVE, BSEL 1)
MK·2705

Figure 0-2

Modem Control (Start)

D-5

HALF· DUPLEX

FULL·DUPLEX

t
RECEIVER NOT
ACTIVE

CWTIMR
=0

NO LINE ERRORS
ENCOUNTERED

LINE ERRORS
ENCOUNTERED

CD = OFF

CTS =0

CTSTMR = 0

NO TIFY USER OF
ST REAMING
STATION
CTS=ON

CTS TIMR=O

CD = OFF

t
RTS=OFF

RTS = ON

TRANSMIT
CTS=OFF

END OF TRANS

FDX

CTS=OFF

HDX

NOTES:
[3.1] CWTIMR·· CARRIERWAITTIMER.ITDETECTSTHECONDITIONWHERETHELINKWASNOTRELINQUISHED IN
TIME BYTHE REMOTE END.
[3.2] CTSTMR •• CLEAR TO SEND TIMER. TIME CLEAR TO SEND GOING AWAY WHEN DROPPING RTS BECAUSE OF LINE
ERRORS. FALL·OUT COVERS CONDITION OF CONSTANT CTS MODEMS.
[3.3]IN FULL DUPLEX MODE·· DMP11 ASSERTS RTS CONSTANTLY. RTS IS DROPPED ONLY WHEN THERE ARE LINE
ERRORS.
[3.4] SOFTWARE INTERLOCK· CONDITION IS SWITCH SELECTABLE FOR CONSTANT CTS MODEMS.
MK·270e

Figure D-3

Modem .Control (Transmit)

D-6

(TRANSMIT 2 )

I
LESS THAN 24 REQUEST
REMOTE PROG RAM LOAD
MESSAGES SENT

24 REQUEST REMOTE PROGRAM
LOAD MESSAGES SENT

TIMER = 0

MK-2703

Figure D-4

Modem Control (Transmit 2)

D-7

(

RECEIVE)

HALF-DUPLEX

FULL-DUPLEX

t
TRANSMITTER NOT
ACTIVE
IN HALF DUPLEX, LINE UNIT
PROVIDES INTERLOCK TO
ENABLE RCV CLOCK ONLY IF
TRANSMITTER IS IDLE.
(RTS =OFF)

CD= ON
SYNC'ED ON NEW
FRAME

_ _ _ _ _ _ _ CD DROPPED IN THE
MIDDLE OF DATA
CD - OFF
- - - - - - STREAM
RESET CDTIMR
TO 1.28 SEC

CD- ON

CDTIMR - 0
NOTIFY USER OF
CARRIER LOSS
(CONTROL RESPONSE)

END OF
RECEIVE

MK·2704

Figure D-S

Modem Control (Receive)

D-8

(

[6.1]

MOD STAT)

WRITE MODEM
STATUS

READ MODEM
STATUS

[6.2]

~----------------.~~~4~--------------~
[6.2]
WRITEABLE MODEM SIGNALS:

[6.1]
READABLE MODEM SIGNALS:
CARRIER
CLEAR TO SEND
MODEM READY (DSR)
HALF DUPLEX
REQUEST TO SEND
DATA TERMINAL READY
RING
TEST MODE

DATA TERMINAL READY

MK·2702

Figure D-6

Modem Control (Modem Status)

D-9

VALID MESSAGE
RECEIVED FOR
THIS STATION

SET CALTMR
= OFF

CALL TIMER = 0

~
,
RESET RECEIVER
AND
TRANSMITTER

I TIMER-10 SECI

TIMER = 0

NOTE: CALTMR = ON
MK-1967

Figure D-7

Modem Control (Call Timer)

0-10

(SHUT DOWN)

CLEAR DTR
AND RTS

RESET RECEIVER
AND TRANSMITIER

BOOTING

REMOTE LOAD
DETECT

CALL TI M R=ON

TIMR~10 SEC

TIMR=O

SET DTR

A
MK·2ee5

Figure D-8

Modem Control (Shutdown)

D-11

DMV11 Synchronous Controller Technicar Manual
EK-DMV11-TM-001

Reader's Comments

Your comments and suggestions will help us in our continuous effort to improve the quality and usefulness of our publications.
What is your general reaction to this manual? In your judgement is it complete, accurate, well organized,
well written, etc? Is it easy to use?~~~~~~~~~~~~~~~~~~~~~~~~~~~

What features are most useful?~_~_~~~~_~~~~_~_~~~~_ _~~~_~~_

What faults or errors have you found in the manual?~_~_~_ _ _ _~~~~_~~~~~~_

Does this manual satisfy the need you think it was intended to satisfy? _ _ _ _ _ _ _ _ _ _ _ _ __
Does it satisfy your needs? _ _ _ _ _ _ _ _ _ _ Why? _ _ _~~~_~~~~~~~_~~_

Please send me the current copy of the Technical Documentation Catalog, which contains information
on the remainder of DIGITAL's technical documentation.
'

Name __~~__~~~~__~__~____~~~___
Title _______~_____~~__~~__~~~~_
Company_~__________~~~~~~~__~___
Department _~~~~~~~~________~___

Street
_______________________
City
_ _ _ _ _ _ _ _ _ _ _ _ _ _ __
_~

State/Country _ _ _~~~_~~~______
Zip __~____~__~__~__~__~~~_______

Additional copies of this document are available from:

Digital Equipment Corporation
444 Whitney Street
Northboro, MA 01532
Attention:

Order No.

Printing and Circulation Services (NR2/M15)
Customer Services Section

EK-DMV11-TM-001

- _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ,_ _ _ _ .Fold H e r e - - - - - - , - - - - - - - - - - - - - - -

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 00 Not Tear - Fold Here,and S t a p l e - - - - - - - - - - - - - - - - -

I IIII I

BUSINESS REPLY MAIL
FIRST CLASS

PERMIT NO. 33

MERRIMACK. NH

POST AGE WILL BE PAID BY ADDRESSEE

Digital Equipment Corporation
Educational Services Development & Publishing
Continental Blvd. (MK1/2M26)
Merrimack, N.H. 03054

No Postage
Necessary
if Mailed in the
United States

Digital Equipment Corporation. Bedford, MA 01730