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EK-RX02-UG-001

July 1978

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Document:	RX02 Floppy Disk System User's Guide
Order Number:	EK-RX02-UG
Revision:	001
Pages:	82
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EK-RX02-UG-001

RX02 Floppy Disk
System
User's Guide

digital equipment corporation • maynard, massachusetts

1st Edition, July 1978

Copyright © 1978 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 DIGIT At's DECset-8000 computerized
typesetting system.

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

PDP
DECUS
UNIBUS

D ECsystem- \0
DECSYSTEM-20
DIBOL
EDUSYSTEM
VAX
VMS

MASSBUS
OMNIBUS
OS/8
RSTS
RSX
lAS

11/82·15

CONTENTS
Page
PREFACE
CHAPTER 1

GENERAL INFORMATION

l.l
1.2
1.2.1
1.2.2
1.2.3
1.2.4
1.2.S
1.3
1.3.1

1.3.2.1
1.3.2.2
1.3.2.3
1.4
I.S
I.S.1
I.S.2
\.S.2.1
I.S.2.2
I.S.3
I.S.3.1
I.S.3.2
I.S.3.3
I.S.3.4

INTRODUCTION .............................................................................................. 1-1
GENERAL DESCRI·PTION ............................................................................... 1-2
Interface Modules ........................................................................................ 1-2
Microprogrammed Controller ...................................................................... I-S
Read/Write Electronics ................................................................................ I-S
Electromechanical Drive .............................................................................. 1-S
Power Supply ............................................................................................... 1-6
OPTION DESCRIPTION ................................................................................... 1-6
Operation For Single Density Recording Only (RX8 E, RX II,
RXVII) ........................................................................................................ 1-7
PDP-8 Operation .................................................................................. 1-7
PDP-II Operation ................................................................................ 1-7
LSI-II Operation ................................................................................. 1-7
Operation For Single or Double Density Recording (RX28,
RX211, RXV21) ........................................................................................... 1-7
PDP-8 Operation .................................................................................. \-7
PDP-II Operation ................................................................................ 1-7
LSI-II Operation ................................................................................. 1-7
SPECIFICATIONS ............................................................................................. 1-7
SYSTEMS COMPATIBILITY ............................................................................ 1-9
Media ........................................................................................................... 1-9
Recording Scheme ...................................................................................... 1-1 0
Double Frequency (FM) ..................................................................... 1-1 0
Miller Code (MFM) ........................................................................... 1-10
Logical FormaL .......................................................................................... 1-12
Header Field Description .................................................................... 1-12
Data Field Description ....................................................................... 1-13
Track Usage ....................................................................................... 1-13
CRC Capability .................................................................................. 1-13

CHAPTER 2

INSTALLATION

2.1
2.1.1
2.1.2
2.1.3
2.1.3.1

SITE PREPARATION ........................................................................................ 2-1
Space ............................................................................................................ 2-1
Cabling ........................................................................................................ 2-2
AC Power. .................................................................................................... 2-2
Power Requirements ............................................................................ 2-2

1.3.1.1
1.3.1.2
1.3.1.3
1.3.2

III

CONTENTS (Cont)
Page
2.1.3.2
2.1.4
2.2
2.3
2.3.1
2.3.2
2.3.3
2.3.4
2.3.5
2.4
2.4.1
2.4.2
2.4.3
2.4.3.1
2.4.3.2
2.4.3.3
2.5
2.5.1
2.6

Input Power Modification Requirements .............................................. 2-3
Fire and Safety Precautions .......................................................................... 2-3
CONFIGURATION GUIDELINES .................................................................. 2-3
ENVIRONMENTAL CONSIDERA TIONS ....................................................... 2-4
General ........................................................................................................ 2-4
Temperature, Relative Humidity .................................................................. 2-4
Heat Dissipation ....... '" ................................................................................ 2-5
Radiated Emissions ...................................................................................... 2-5
Cleanliness ................................................................................................... 2-5
UNPACKING AND INSPECTION ................................................................... 2-5
General ........................................................................................................ 2-5
Tools ............................................................................................................ 2-6
Unpacking ................................................................................................... 2-6
Cabinet-Mounted ................................................................................. 2-6
Separate Container ............................................................................... 2-6
Inspection ............................................................................................ 2-8
INSTALLATION ................................................................................................ 2-8
PDP8-A Modification ................................................................................ 2-10
TESTING .......................................................................................................... 2-10

CHAPTER 3

USER INFORMATION

3.1
3.2
3.2.1
3.2.2
3.2.2.1
3.2.2.2
3.2.3
3.3
3.4

CUSTOMER RESPONSIBILITy ....................................................................... 3-1
CARE OF MEDIA .............................................................................................. 3-1
Handling Practices and Precautions .............................................................. 3-1
Diskette Storage ........................................................................................... 3-2
Short Term (Available for Immediate Use) ........................................... 3-2
Long Term ........................................................................................... 3-2
Shipping Diskettes ........................................................................................ 3-2
OPERATING INSTRUCTIONS ........................................................................ 3-3
OPERATOR TROUBLESHOOTING ................................................................ 3-3

CHAPTER 4

PROGRAMMING

4.1
4.1.1
4.1.2
4.1.2.1
4.1.2.2
4.1.2.3
4.1.2.4
4.1.2.5
4.1.2.6
4.1.2.7
4.1.2.8

RX8E AND RX28 Programming Information .................................................... .4-1
Device Codes ............................................................................................... .4-1
Instruction Set .............................................................................................. 4-2
RX8E Load Command (LCD) ............................................................ .4-2
RX28 Load Command ........................................................................ .4-3
Transfer Data Register (XDR) ............................................................ .4-3
STR ..................................................................................................... 4-3
SER ..................................................................................................... 4-4
SDN ..................................................................................................... 4-4
INTR ................................................................................................... 4-4
INIT .................................................................................................... 4-4
iv

CONTENTS (Cont)
Page
4.1.3
4.1.3.1
4.1.3.2
4.1.3.3
4.1.3.4
4.1.3.5
4.1.3.6
4.1.3.7
4.1.4
4.1.4.1
4.1.4.2
4.1.4.3
4.1.4.4
4.1.4.5
4.1.4.6
4.1.4.7
4.1.4.8
4.1.4.9
4.1.4.10
4.1.5
4.1.5.1
4.1.5.2
4.1.6
4.1.6.1
4.1.6.2
4.1.6.3
4.1.7
4.1.8
4.2
4.2.1
4.2.2
4.2.2.1
4.2.2.2
4.2.2.3
4.2.2.4
4.2.2.5
4.2.2.6
4.2.3
4.2.3.1
4.2.3.2
4.2.3.3
4.2.3.4
4.2.3.5
4.2.3.6
4.2.3.7

Register Description ..................................................................................... 4-4
Command Register ............................................................................... 4-4
Error Code Register ............................................................................. 4-5
RX2T A - RX Track Address ............................................................... .4-6
RX2SA - RX Sector Address .............................................................. .4-6
RX2DB - RX Data Buffer ................................................................... .4-6
RX8E - RX Error and Status ............................................................... 4-6
RX28 - RX Error and Status ............................................................... .4-7
Function Code Description ......................................................................... .4-8
Fill Buffer (000) .................................................................................... 4-9
Empty Buffer (001) ............................................................................... 4-9
Write Sector (010) ................................................................................ .4-9
Read Sector (011) ............................................................................... 4-1 0
Set Media Density (100) for RX28 only .............................................. .4-1 0
Maintenance Read Status (101) for RX28 only ................................... .4-IO
Read Status (101) for RX8E only ....................................................... .4-10
Write Deleted Data Sector (110) ........................................................ .4-11
Read Error Code Function (111 ) ........................................................ .4-11
Power Fail .......................................................................................... 4-11
Error Recovery ........................................................................................... 4-1 I
RX8E ....................................................................... : ......................... 4-11
RX28 .................................................................................................. 4-12
RX8E Programming Examples ................................................................... 4-13
Write/Write Deleted Data/Read Functions ........................................ 4-13
Empty Buffer Function ...................................................................... .4-13
Fill Buffer Function ............................................................................ 4-13
RX28 Programming Examples ................................................................... .4-17
Restrictions and Programming Pitfalls ....................................................... .4-22
RXII AND RXVII PROGRAMMING INFORMATION .............................. 4-23
Register and Vector Addresses .................................................................... 4-23
Register Description ................................................................................... 4-24
RXCS - Command and Status (177170) .............................................. 4-24
RXDB - Data Buffer Register (177172) .............................................. 4-25
RXT A - RX Track Address ............................................................... .4-25
RXSA - RX Sector Address .............................................................. .4-25
RXDB - RX Data Buffer ................................................................... .4-25
RXES - RX Error and Status ............................................................. 4-26
Function Codes .......................................................................................... 4-27
Fill Buffer (000) .................................................................................. 4-27
Empty Buffer (001) ............................................................................. 4-27
Write Sector (010) ............................................................................... 4-28
Read Sector (011) ............................................................................... 4-28
Read Status (101) ................................................................................ 4-29
Write Sector with Deleted Data (110) .................................................. 4-29
Read Error Code Function (111) ......................................................... 4-29

CONTENTS (Cont)

Page
4.2.3.8
4.2.4
4.2.4.1
4.2.4.2
4.2.4.3
4.2.5
4.2.6
4.3
4.3.1
4.3.2
4.3.2.1
4.3.2.2
4.3.2.3
4.3.2.4
4.3.2.5
4.3.2.6
4.3.2.7
4.3.2.8
4.3.3
4J.3.1
4.3.3.2
4.3.3.3
4.3.3.4
4.3.3.5
4.3.3.6
4.3.3.7
4.3.3.8
4.3.3.9
4.3.4
4.3.5
4.3.5.1
4.3.5.2

Power Fail .......................................................................................... 4-29
Programming Examples .............................................................................. 4-30
Read Data/Write Data ...................................................................... .4-30
Empty Buffer Function ...................................................................... .4-30
Fill Buffer Function ............................................................................ 4-30
Restrictions and Programming Pitfalls ........................................................ 4-30
Error Recovery ........................................................................................... 4-34
RX211 AND RXV21 PROGRAMMING INFORMATION ............................ 4-34
Register and Vector Addresses ................................................................... .4-35
Register Description ................................................................................... 4-35
RX2CS - Command and Status (177170) ............................................ 4-35
RX2D B - Data Buffer Register (177172) ............................................ .4-36
RX2TA - RX Track Address .............................................................. 4-37
RX2SA - RX Sector Address ............................................................. .4-37
RX2WC - RX Word Count Register .................................................. 4-37
RX2BA - RX Bus Address Register ................................................... .4-37
RX2DB - RX Data Buffer ................................................................. .4-37
RX2ES - RX Error and Status ............................................................ 4-38
Function Codes .......................................................................................... 4-39
Fill Buffer (000) .................................................................................. 4-39
Empty Buffer (00 I) ............................................................................ .4-39
Write Sector (010) .............................................................................. .4-39
Read Sector (011) ............................................................................... 4-40
Set Media Density (100) ...................................................................... 4-41
Maintenance Read Status (101 ) ........................................................... 4-41
Write Sector with Deleted Data (110) ................................................. .4-41
Read Error Code (III) ....................................................................... .4-41
RX02 Power Fail ................................................................................ 4-42
Error Recovery ........................................................................................... 4-43
RX211/RXV21 Programming Examples ................................................... .4-43
Write/Fill Buffer ................................................................................ 4-43
Read/Empty Buffer ........................................................................... .4-45

FIGURES
Figure No.

I-I
1-2
1-3
1-4

Title

Page

Floppy Disk Configuration .................................................................................. 1-3
Front View of the Floppy Disk System ................................................................ .1-3
Interface Modules ................................................................................................ 1-4
Top View of RX02 ............................................................................................... 1-5

FIGURES (Cont)
Figure No.
1-5
1-6
1-7
1-8
1-9
1-10
2-1
2-2
2-3
2-4
2-5
2-6
4-1
4-2
4-3
4-4
4-5
4-6
4-7
4-8
4-9
4-10
4-11
4-12
4-13
4-14
4-15
4-16
4-17
4-18
4-19
4-20
4-21
4-22
4-23
4-24
4-25
4-26
4-27
4-28
4-29
4-30
4-31
4-32

Title

Page

Underside View of Drive ...................................................................................... 1-6
Diskette Media ..................................................................................................... 1-9
Flux Reversal Patterns for FM ........................................................................... 1-1 0
FM versus MFM Encoding ................................................................................ 1-11
Track Format (Each Track) ................................................................................ 1-12
Sector Format (Each Sector) ............................................................................... 1-12
RX02 Outline Dimensions .................................................................................... 2-1
Cabinet Layout Dimensions ................................................................................. 2-2
RX02 Rear View .................................................................................................. 2-3
RX02 Unpacking ................................................................................................. 2-7
RX02 Cabinet Mounting Information .................................................................. 2-7
KM8-A Modification ......................................................................................... 2-1 0
LCD Word Format (RX8E) ................................................................................ .4-2
Command Word Format (RX28) ........................................................................ .4-3
Command Register Format (RX8E) .................................................................... .4-4
Command Register Format (RX28) .................................................................... .4-4
Error Code Register Format (RX8E/RX28A) ...................................................... 4-5
RX2T A Format (RX8E/RX28A) ....................................................................... .4-6
RX2SA Format (RX8E/RX28) ........................................................................... .4-6
RX2DB Format (RX8E/RX28) .......................................................................... .4-7
RXES Format (RX8E) ......................................................................................... 4-7
RX2ES Format (RX28) ........................................................................................ 4-8
RX8E Write/Write Deleted Data/Read Example ............................................... 4-15
RX8E Empty Buffer Example ............................................................................ .4-17
RX8E Fill Buffer Example ................................................................................. .4-18
RX28 Write/Write Deleted Data/Read Example .............................................. .4-19
RX28 Fill Buffer Example .................................................................................. 4-21
RX28 Empty Buffer Example ............................................................................ .4-22
RXCS Format (RXII /RXV 11) ......................................................................... .4-25
RXTA Format (RX11/RXVll) ........................................................................ .4-26
RXSA Format (RX II /RXV 11) .......................................................................... 4-26
RXDB Format (RXII /RXV 11) ......................................................................... 4-26
RXES Format (RX II /RXV II) ......................................................................... .4-27
RXII/RXVII Write/Write Deleted Data/Read Example .................................. 4-32
RXII/RXVII Empty Buffer Example ............................................................... .4-33
RXII/RXVII Fill Buffer Example .................................................................... .4-34
RX2CS Format (RX211/RXV21) ...................................................................... 4-36
RX2T A Format (RX21 I /RXV21 ) ...................................................................... 4-38
RX2SA Format (RX211 /RXV21) ...................................................................... 4-38
RX2WC Format (RX211/RXV21) .................................................................... .4-38
RX2BA and RX2DB Format (RX211/RXV21) ................................................. 4-38
RX2ES Format (RX211/RXV21) ..................................................................... .4-39
RX211/RXV21 Write/Fill Buffer Example ........................................................ 4-45
RX211/RXV21 Read/Empty Buffer Example ................................................... .4-46

vii

TABLES
Table No.

1-1
2-1
2-2
2-3
3-1
4-1

Title

Page

Data Address Mark Code ................................................................................... 1-13
RX02 Configurations ........................................................................................... 2-4
Controller Configuration Switch Positions ........................................................... 2-4
Interface Codej Jumper Configuration ................................................................. 2-9
Operator Troubleshooting Guide ......................................................................... 3-3
Device Code Switch Selection ............................................................................... 4-2

viii

PREFACE

This manual is intended to provide the user with sufficient information to correctly set up and operate
the RX02 Floppy Disk System in any of the various configurations that are available for use with the
PDP-8, PDP-II, or LSI-II computers. The manual presents general, installation, user, and programming information for the RX02 Floppy Disk System and the interface options associated with the
PDP-8, PDP-II, and LSI-II computer systems.

CHAPTER 1
GENERAL INFORMATION

1.1 INTRODUCTION
The RX02 is a low cost, random access mass memory device that stores data in fixed length blocks on
flexible diskettes with preformatted industry standard headers. The RX02 interfaces with either a
PDP-8, a PDP-II, or an LSI-II system. Various interface modules are selected according to the computer being used and either single or double density recording. The various configurations are:

Designation

Computer

Interface
Module

Recording
Density

RX8E
RX28
RXll
RX211
RXVII
RXV21

PDP-8
PDP-8
PDP-II
PDP-ll
LSI-ll
LSI-II

M8357
M8357
M7846
M8256
M7946
M8029

Single
Single or Double
Single
Single or Double
Single
Single or Double

NOTE
The single density recording configurations RX8E,
RXn, and RXVH are compatible with the RXOI
Floppy Disk System when the M7744 controller
module has been switched to be compatible with
these configurations. (See Table 2-2.)

The RX02 consists of two flexible disk drives, a single read/write electronics module, a microprogrammed controller module, and a power supply, enclosed in a rack-mountable, 10-1/2 inch, selfcooled chassis. A cable is included for connection to either a PDP-8 interface module, a PDP-II
interface module, or an LSI-II interface module. The amount of data that can be stored on the RX02
varies according to the configuration. The recording density can be different for each drive. For each
drive system using double density recording, up to 512K 8-bit bytes of data (PDP-8, PDP-II, LSI-II)
or 256K 12-bit words (PDP-8) can be stored and retrieved. For each drive system using single density
recording, up to 256K 8-bit bytes of data or 128K 12-bit words (PDP-8) can be stored and retrieved.
The RX02 interfaces with IBM-compatible devices when single density data recording is used.

I-I

For single or double density recording, the RX02 is used with either an M8357 interface module (PDP8), an M8256 interface module (PDP-II), or an M8029 interface module (LSI-II). The interface modules convert the RX02 I/O bus to the bus structure of the computer being used. Each module controls
the interrupts to the CPU initiated ~y the RX02 and handles the data interchange between the RX02
and the host computer. Each interface module is powered by the host processor.

In addition, the RX02 is used for single density recording when it is configured to be compatible with
the RXOI. The interface module used is either an M8357 (PDP-8), an M7846 (PDP-II), or an M7946
(LSI-II ).

To record or retrieve data the RX02 performs implied seeks. Given an absolute sector address, the
RX02 locates the desired sector and performs the indicated function, including automatic head position verification and hardware calculation and verification of the cyclic redundancy check (CRq
character. The CRC character that is read and generated is compatible with IBM 3740 equipment.

1.2 GENERAL DESCRIPTION
An RX02 Floppy Disk System consists of the following components:
M7744 Controller Module
M7745 Read/Write Electronics Module
. H77I-A, -C, or -0 Power Supply
RX02-CA Floppy Disk Drive (60 Hz max of 2)
RX02-CC Floppy Disk Drive (50 Hz max of 2)

One interface module is used:
M8357 (PDP-8, Programmed I/O)
M7846 (pDP-II, Programmed I/O)
M7946 (LSI-II, Programmed I/O)

M8256 (PDP-II with DMA)
M8029 (LSI-II with DMA)

All components except the interface modules are housed in a 10-1/2 inch rack-mountable box. The
power supply, M7744 module, and M7745 module are mounted above the drives. Interconnection
from the RX02 to the interface is with a 40-conductor BC05L-15 cable of standard length (I5 ft).
Figure 1-1 is a configuration drawing of the system: part A shows the configuration for a bus interface
with DMA; part B shows the configuration for all Omnibus interfaces (programmed I/O); part C
shows the configuration for a bus interface (programmed I/O) that is RXOI compatible. Figure 1-2 is a
front view of a dual drive system.

1.2.1 Interface Modules
The interface modules plug into a slot on the bus for PDP-8, PDP-II, and LSI-II computers. Figure
1-3 shows the outline of the various modules and areas of interest on each module.

1-2

L
MB029
BUS
INTERFACE

DISKETTE
IA 7015·580
"CPU
CONTROLLER
M7744 •

MB256
UNIBUS
INTERFACE

DISKETTE

I S I
I
I B I LSI·l1
IUI
I S I

IUI
I ~ I PDP·ll
I B I
I U I
S

A. BUS INTERFACE WITH DMA

t========i'I I M I
M8357
OMNIBUS
INTERFACE

I NI I PDP·8
IBI
I U I

"CPU
CONTROLLER
M7744 •

B. OMNIBUS INTERFACE, PROGRAMMED 1/0
M8357
OMNIBUS
INTERFACE

M
I N I
II
I

I S

"CPU
CONTROLLER
M7744 •

I PDP·B

~ I
I

P======'i'I I ~ I
M7846
II I
UNIBUS
PDP·l1
IB I
INTERFACE

U
'--_ _ _ _ _-.JI I S I

1'=-====="11 I L I
I

M7946
S I
BUS
I I LSI·l1
INTERFACE
I B
L-_ _ _ _ _JI I U I

POWER
SUPPLY H771

C. BUS INTERFACE, PROGRAMMED 1/0 (RXOl COMPATIBLE)
• A SWITCH ON THIS MODULE IS POSITIONED TO BE COMPATIBLE WITH THE INTERFACE.

S
MA·1857

Figure I-I

Floppy Disk Configuration

III!IDIIRX02

Figure 1-2

Front View of the Floppy Disk System

1-3

M7946 MOIJULE IRXV11)

r------ J ------,
CABLE CONNECTION

BC05L·15
CABLE CONNECTION

r, 1

Wl .. W3
W2 .. W5
W4 .. W6
W7 .•• W13
W8 ... W14
W19 .. W9
W16 .. W9
Wl0 .. W17
Wl' •• W15
W12 ..

... W8
... W9
... W10

... Wl
... W2
... W3
... W4
... W5
... W6

ADDRESS
JUMPERS

... Wll
... W12

A12

0\ ~ I~
00 . . .

00
00

~o::
VB

......

REV C & REV D

REV B

•

Al1

MB029 MODULE IRXV21)

.t;..

CABLE CONNECTION

DEVICE CODE SWITCH

PRIORITY PLUG

CABLE CONNECTION

ADDRESS
SWITCH
OFF=1

PRIORITY PLUG

o
<

VECTOR
SWITCH
ON=1

111111
M8357 MODULE IRX8E OR RX28)

BC05L·15
CABLE CONNECTION

M8256 MODULE I RX21 N

M7846 MODULE IRX11)

MA·2710

Figure 1-3

Interface Modules

1.2.2 Microprogrammed Controller
The M7744 microprogrammed controller module is located in the RX02 cabinet as shown in Figure
1-4. The M7744 is hinged on the left side and lifts up for access to the M7745 read/write electronics
module.
1.2.3 Read/Write Electronics
The M7745 read/write electronics module is located in the RX02 cabinet as shown in Figure 1-4.

MA 1751

Figure 1-4

Top View of RX02

1.2.4 Electromechanical Drive
A maximum of two drives can be attached to the read/write electronics. The electromechanical drives
are mounted side by side under the read/write electronics board (M7745). Figure 1-5 is an underside
view of the drive showing the drive motor connected to the spindle by a belt. (This belt and the drive
pulley are different on the 50 Hz and 60 Hz units; see Paragraph 2.1.3.2 for complete input power
modification requirements.)

1-5

DRIVE MOTOR
BELT

MA-1850

Figure \-5

Underside View of Drive

1.2.5 Power Supply
The H771 power supply is mounted at the rear of the RX02 cabinet as shown in Figure 1-4. The
H771-A is rated at 60 Hz ± 1/2 Hz over a voltage range of90-128 Vac. The H771-C and -0 are rated
at 50 Hz + 1/2 Hz over four voltage ranges:
90-120 Vac
3.5 A circuit breaker; H771-C
100-128 Vac
184-240 Vac
1.75 A circuit breaker; H771-0
200-256 Vac
Two configuration plugs are provided to adapt the H77I-C or -0 to each voltage range. This is not
applicable to the H77I-A.

1.3 OPTION DESCRIPTION
The optional interface modules that are used to interface the RX02 with a PDP-8, PDP-II, and LSI-II
are listed in Paragraphs 1.1 and 1.2. (Each module is powered by the host processor.) The module
selected is determined by the computer being used and whether the data interchange is between either
IBM system 3740 compatible devices or DIGITAL system double density devices. Also, when an
M7744 controller module's configuration switch is set to be compatible, the RX02 can operate as an
RXOI. The RX02 interfaces with IBM compatible devices when single density data recording is used.
The RX02 interfaces with DIGITAL system double density recording devices when the controller
module configuration switch is positioned to be compatible with RX28, RX211, and RXV21 configurations.

1-6

1.3.1

Operation For Single Density Recording Only (RX8E, RXll, RXVll)

1.3.1.1 PDP-8 Operation - The RX02 connects to the M8357 Omnibus interface module. This module converts the RX02 I/O bus to PDP-8 family Omnibus structure. It controls interrupts to the CPU
initiated by the RX02, controls data interchange between the RX02 and the host CPU by programmed
I/O, and handles input/output transfers used for maintenance status conditions.
1.3.1.2 PDP-II Operation - The RX02 connects to the M7846 Unibus interface module. This module
converts the RX02 I/O bus to PDP-II Unibus structure. It controls interrupts to the CPU initiated by
the RX02, decodes Unibus addresses for register selection, and handles data interchange between the
RX02 and the host CPU main memory by programmed I/0.
1.3.1.3 LSI-II Operation - The RX02 connects to the M7946 LSI-II bus interface module. This
module converts the RX02 I/O bus to the LSI-II bus structure. It controls interrupts to the CPU
initiated by the RX02, decodes LSI-II bus addresses for register selection, and transfers data between
the RX02 and the host CPU main memory by programmed I/O.
1.3.2

Operation For Single or Double Density Recording (RX28, RX211, RXV2l)

1.3.2.1 PDP-8 Operation - The RX02 connects to the M8357 Omnibus interface module. This module converts ¥he RX02 I/O bus to PDP-8 family Omnibus structure. It controls interrupts to the CPU
initiated by the RX02, controls transfer of data between the RX02 and host CPU by programmed I/O,
and handles input/output transfer used to test status conditions.
1.3.2.2 PDP-II Operation - The RX02 connects to the M8256 Unibus interface module. This module
converts the RX02 I/O bus to PDP-II Unibus structure. It controls interrupts to the CPU initiated by
the RX02, decodes Unibus addresses for register selection, and initiates NPR requests to transfer data
between the RX02 and the host CPU main memory.
1.3.2.3 LSI-ll Operation - The RX02 connects to the M8029 LSI-II bus interface module. This
module converts the RX02 I/O bus to the LSI-II bus structure. It controls interrupts to the CPU
initiated by the RX02, decodes LSI-II bus addresses for register selection, and initiates NPR requests
to transfer data between the RX02 and the host CPU main memory.
1.4 SPECIFICATIONS
System Reliability
Minimum number of revolutions per track
Seek error rate
Soft data error rate
Hard data error rate

3 million/media (head loaded)
I in 1()6 seeks
1 in 109 bits read or written
1 in 10 12 bits read or written

NOTE
The above error rates only apply to DEC approved
media that is properly cared for. Seek error and soft
data errors are usually attributable to random effects
in the head/media interface, such as electrical noise,
dirt, or dust. Both are called "soft" errors if the error is recoverable in 10 additional tries or less.
"Hard" errors cannot be recovered. Seek error retries should be preceded by a recalibrate.

1-7

Drive Performance
8-bit bytes
256,256
512,512
3,328
6,656
128
256

Recording
FM
MFM
FM
MFM
FM
MFM

Capacity
Per diskette
Per track
Per sector

Data transfer rate
Diskette to controller buffer
Buffer to CPU interface

12-bit words
128,128
256,256
1,664
3,328

64
128

4 ~s/data bit (FM)
2 ~s/data bit (MFM)
1.2 ~s/bit

NOTE
PDP-8 interface can operate in 8- or 12-bit modes
under software control.

Track-to-track move
Head settle time
Rotational speed
Recording surfaces per disk
Tracks per disk
Sectors per track
Recording technique
Bit density maximum on
inner track
Track density
A verage access

6 ms/track maximum
25 ms maximum
360 rpm ± 2.5%; 166 ms/rev nominal
1
77 (0-76) or (0-1148)
26 (1-26) or (0-328)
Double frequency (FM) or modified MFM
3200 bpi (FM) or modified (MFM)
48 tracks/inch
262 ms, computed as follows:
Seek
Settle

"f),

77 tks/3 X 6 ms

,...-____
.A_ _ _ ___
Rotate
,

+ 25 ms

r+ 166 ms/2 = 262 ms"

Environmental Characteristics
Temperature
RX02, operating
RX02, nonoperating
Media, nonoperating

15 0 to 32 0 C (59 0 to 90 0 F) ambient;
maximum temperature gradient = 11 0 C/hr (20 0 F /hr)
-35 0 to +60 0 C (-30 0 to + 140 0 F)
-35 0 to +52 0 C (_30 0 to + 125 0 F)

NOTE
Media temperature must be within operating temperature range before use.

Heat Dissipation (RX02 System)
Relative humidity
RX02, operating

Less than 225 Btu/hr
25 0 C (77 0 F) maximum wet bulb
2 0 C (36 0 F) minimum dew point
20% to 80% relative humidity
1-8

RX02, nonoperating
Media, nonoperating
Magnetic field
Interface modules
Operating temperature
Relative humidity
Maximum wet bulb
Minimum dew point

5% to 98% relative humidity (no condensation)
10% to 80% relative humidity
Media exposed to a magnetic field strength of 50 oersteds or
greater may lose data.
50 to 50 0 C (41 0 to 122 0 F)
10% to 90%
32 0 C (90 0 F)
2 0 C (36 0 F)

Electrical
Power consumption
RX02
PDP-II interface (M7846,
M8256)
PDP-8 interface (M8357)
LSI-II interface (M7946,
M8029)
AC power

5 A at +5 Vdc, 25 W; 0.14 A at -5 Vdc, 0.7 W; 1.3 A t +24 Vdc,
31 W
1.8 A at 5 Vdc
1.5 A at 5 Vdc
1.8 A at 5 Vdc
4 A at 115 Vac
2 A at 230 Vac

1.5 SYSTEMS COMPATIBILITY
This section describes the physical, electrical, and logical aspects of compatibility for data interchange
with IBM system 3740 devices and for data interchange with double density devices.
1.5.1 Media
The media used on the RX02 Floppy Disk system is compatible with the IBM 3740 family of equipment and is shown in Figure 1-6. The "diskette" media was designed by applying tape technology to
disk architecture, resulting in a flexible oxide-on-mylar surface. The diskette is encased in a plastic
envelope with a hole for the read/write head, a hole for the drive spindle hub, and a hole for the hard
index mark. The envelope is lined with a fiber material that cleans the diskette surface. The media is
supplied to the customer preformatted and pretested.
INDEX HOLE

o
}4!-_ _ _ _+REGISTRATION

HOLE

READIWRITE
I " ' - - - - - + H E A D APERTURE

MA 1750

Figure 1-6 Diskette Media

1-9

1.5.2 Recording Scheme
. There are two recording schemes used in the RX02: double frequency (FM) and modified Miller code
(MFM). The FM scheme is used for single density data recording which is compatible with IBM
system 3740 devices. (When this recording scheme is used and the RX02 is configured as shown in
Figure I-I part C, the RX02 is compatible with the RXOl.) The MFM scheme is used for double
density data recording which is compatible with DIG IT AL double density devices but is not compatible with other manufacturers.
1.5.2.1 Double Frequency (FM) - For the double frequency recording scheme data is recorded between bits of a constant clock stream. The clock stream consists of a continuous pattern of one flux
reversal every four JLS (Figure 1-7). A data "one" is indicated by an additional reversal between clocks
(i.e., doubling the bit stream frequency; hence the name). A data "zero" is indicated by no flux reversal
between clocks.
A continuous stream of ones, shown in the bottom waveform in Figure 1-7, would appear as a "2F"
bit stream, and a continuous stream of zeros, shown in the top waveform in Figure 1-7, would appear
as a "IF" or fundamental frequency bit stream.

ALL ZEROS
PATTERN

0 1I 0
I

I
I
I

I
I

--I 4 11 SCC I--

CHANGING
PATTERN

o I

ALL ONES

, PATTERN
1

1
I
CP·l$06

Figure 1-7

Flux Reversal Patterns for FM

1.5.2.2 Miller Code (MFM) - MFM or Miller code encodes clocks between data bits of a continuous
data stream. The data stream consists of flux reversals for a data "one" and no flux reversal for a data
"zero." A clock is recorded only between data "zeros." Because it is possible to have double density
data fields map into a preamble and ID mark, the MFM encoding is modified slightly to prevent a
false header from being detected within a double density data field.
NOTE
The modified MFM encoding is not compatible with
other manufacturers.

The encoding algorithms for implementing modified MFM are:
Encoding Algorithm #1 (MFM or Miller Code Algorithm)
Dn

Data
Dn+ 1

Encoded Data
Dn
Cn

Dn+ 1

0
I
0
I

0
0
I
I

0
I
0
I

0
0
I
I

1-10

I
0
0
0

Encoding Algorithm #2 (MFM Modified Algorithm)

Data

Dn + 1

On + 3

On +2

On + 4

On +5

Encoded Oata
Dn + 3 Cn + 3 On + 4 Cil + 4 On + 5

DI1 + 1 Cn + 1 On + 2 Cn + 2

The decoding algorithm used in data separation is:
Encoded

Decoded

Dil

011 + 1

a
1
a
0
a

0
I

a
1

Dn
I

0
0
1
1

a
I
a

a
a

Figure 1-8 shows the waveforms that are generated for a data stream of zeros and ones when FM code,
MFM code, and modified MFM code are used.

DATA

F M

MFM

MODIFIED
MFM

I'"
DATA"

MODIFYING
ALGORITHM

-----l

0011101111000
i! I! I I I ! I I I
I ! I I I 11 I I I ! I I

I I II I I I I I I I I I

n n

MODIFIED
MFM
-J

r-1 n r
U LJ LJ U

WHERE/DATA' =2JDATA

Figure \-8

FM versus MFM Encoding

1-11

1.S.3

Logical Format

Data is recorded on only one side of the diskette. This surface is divided into 77 concentric circles or
"tracks" numbered 0-76. Each track is divided into 26 sectors numbered 1-26 (Figure 1-9). Each
sector contains two major fields: the header field and the data field (Figure 1-10).

LL.E.D TRAr,SDUCER OUTPUT

HARD
INDEX

MARK

---------------~(A

PRE IN bEX
GA P
320 B

SECTOR

" 26

~"
...

SECTOR

SECCTOR

SECTOH

" 1

" 2

,,~

ins

t
SOFT INDEX MARK
I

1 BYTE
_ROTATIOI,

Figure 1-9

Track Format (Each Track)

HEADER FIELD

r---

DATA FIELD

r -_ _ _ _ _ _ _ _

----"---

~A~

_______

,
«
«

I>L

0(/1

~o
INTER·
-U1
SECTOR GAP LLW
ul26 BYTES
z>l's OR 0'5
>-'"
(f) ' "

o
o

(f)

::;

o
o
«

~
w

""w

ul-

«>-

0:'"

01-

: t;:
p~

HEADER
CRC
2 BYTES

-'W

ill

o >-

0: CD

«>-

128'0 BYTES OF FM
DATA
OR
256, 0 BYTES OF MFM
(MODIFIED)
DATA

DATA
CRC
2 BYTES

« >L
««

1--

f-O:

0::;

~--j

PREAMBLE

11 BYTES-l.-j
10 GAP
l's OR O's

WRITE GATE TURN OFF
FOR WRITE OF PRECEEDING
DATA FIELD

-ROTATION

Figure 1-10

6 BYTES

WRITE GATE TURN ON
FOR WRITE OF NEXT
DATA FIELD

Sector Format (Each Sector)

1.5.3.1 Header Field Description - The header field is broken into seven bytes (eight bits/byte) of
in formation and is preceded by a field of at least six bytes of zeros for synchronization. The header and
its preamble are always recorded in FM.
!.

Byte No. I: ID Address Mark - This is a unique stream offlux reversals (nota string of data
bits) that is decoded by the controller to identify the beginning of the header field, (Data ==
FE hex, clock = C7 hex.)

Byte No, 2: Track Address - This is the absolute (0-1148) binary track address. Each sector
contains track address information to identify its location on 1 of the 77 tracks.

Byte No, 3: - Zeros
1-12

Byte No.4: Sector Address - This is the absolute binary sector address (1-328). Each sector
contains sector address information to identify its circumferential position on a track. There
is no sector O.

Byte No.5: - Zeros

6,7.

Bytes No.6 and 7: eRe - This is the cyclic redundancy check character that is calculated for
each sector from the first five header bytes using the IBM 3740 polynomial.

1.5.3.2 Data Field Description - The data field contains either 13110 or 25910 bytes of information
depending on the recording scheme. This field is preceded by a field of zeros for synchronization and
the header field (Figure 1-10).
I.

Byte No.1: Data or Deleted Data Address mark - This byte is always recorded in FM and is
unique because it contains missing clocks. It is decoded by the controller to identify the
beginning of a data field. The deleted data mark is not used during normal operation but the
RX02 can identify and write deleted data marks under program control as required. There is
a unique address mark for each density as shown in the following table. One of these marks
is the first byte of each data field.
Table 1-1

Data Address Mark Code
Hex Byte

Mark

Density

Data

Clock

MFM mod.

DELETED

DATA

MFM mod.

Data

Bytes No.2: -129 (FM) or -257 (MFM modified) - This is the data field and it can be
recorded in either FM or MFM (modified). It is used to store 12810 or 25610 (depending
upon encoding) 8-bit bytes of information.
NOTE
Partial data fields are not recorded.

Bytes No. 130 and 131 or 258 and 259 - These bytes comprise the eRe character that is
calculated for each sector from the first 129 or 257 data field bytes using the industry standard polynomial division algorithm designed to detect the types of failures most likely to
occur in recording on the floppy media. These bytes wiII be recorded with the same encoding
scheme as the data field.

1.5.3.3 Track Usage - In the IBM 3740 system, some tracks are commonly designated for special
purposes such as error information, directories, spares, or unused tracks. The RX02 is capable of
recreating any system structure through the use of special systems programs, but normal operation will
make use of all the available tracks as data tracks. Any special file structures must be accomplished
through user software.
1.5.3.4 eRe Capability - Each sector has a two-byte header eRe character and a two-byte data
eRe character to ensure data integrity. The eRe characters are generated by the hardware during a
write operation and checked to ensure all bits were read correctly during a read operation. The eRe
character is the same as tJ-.at used in IBM 3740 series equipment.
1-13

CHAPTER 2
INST ALLATION

This chapter contains information that is required for site preparation, unpacking, installation, and
testing of the RX02 Floppy Disk System. Information is also provided to identify the various system
configurations that are available.

2.1

SITE PREPARATION

2.1.1 Space
The RX02 is a cabinet-mountable unit that may be installed in a standard Digital Equipment Corporation cabinet. This rack-mountable version is approximately 28 cm high, (10-1/2 inches), 48 cm wide,
(19 inches) and 42 cm deep (16-1/2 inches) as shown in Figure 2-1.

10.5"

---!--=r
I

1--_ _ _ _ _ _ _ _ _

19"

1<>
..- - - - ( 4 8 . 3 c m ) - - - + l .
(FRONT VIEW)

17.0"
i---(43.2Cm)1

&~" "0" CK

=
(FRONT)

,INSIDE TRA

26.5"
(66.3cm)
(SIDE VIEW)

NOTE:
DUST COVER ATTACHED TO
CABINET NOT RX02
MA·1825

Figure 2-\

RX02 Outline Dimensions

2-1

· When the RX02 is mounted in a cabinet (Figure 2-2), provision should be made for service clearances
of approximately 56 em (22 inches) at the front and rear of the cabinet so that the RX02 can be
extended or the cabinet rear door opened.
WINGING DOOR
R.H. OR L.H.
\

\"SWINGING MOUNTING
\ ':~M.E DOOA A.H. OR L. H.
::::::_-::;.~ -?-'~~,

_ "':::::: _

......

'l'

1/1/

'''"
\ \

18 I""
(46.35cm)

I
1/

"
REMOVABLE
END PANEL

48' /""
(122.47cm)

I
I

I
I
CABLE ACCESS--il-""'1

CASTER SrilVEL
RADIUS 2' In
(6.12 em)
(4) CASTERS

FAN
PORTS

I
,-,,,

.......... /

LEVELER
4 PLACES

It-:

"/"--+1

21
(54.87em)

I
I
I

3.0"
(76.2em)

RX02 EXTENDED
FROM CABINET

I
19"
I
(48.26 em)
~
I

'- _ _ _ _ _ _ JI
I

MA·H12B

CABINET 71 7116" (182.28 em) HIGH
(FLOOR LINE TO CABINET TOP)

Figure 2-2

Cabinet Layout Dimensions

2.1.2 Cabling
The standard interface cable provided with an RX02 (BC05L-15) is 4.6 m (15 ft) in length; the positioning of the RX02 in relation to the central processor should be planned to take this into consideration.
The RX02 should be placed near the control console or keyboard so that the operator will have easy
access to load or unload disks. The position immediately above the CPU is preferred. The ac power
cord is about 2.7 m (9 ft) long.
2.1.3

AC Power

2.1.3.1 Power Requirements - The RX02 is designed to use either a 60 Hz or at 50 Hz power source.
The 60 Hz version will operate from 90-128 Vac, without modifications, and will use less than 4 A
operating. The 50 Hz version will operate within four voltage ratings and will require field verification/modification to ensure that the correct voltage option is selected. The voltage ranges of
90-120 Vac and 184-240 Vac will use less than 4 A operating. The voltage ranges of 100-128 Vac and
200-256 Vac will use less than 2 A. Both versions of the RX02 will be required to receive the input
power from an ac source (e.g., 861 power control) that is controlled by the system's power switch.

2-2

2.1.3.2 Input Power Modification Requirements - The 60 Hz version of the RX02 uses the H77I-A
power supply and will operate on 90-128 Vac, without modification. To convert to operate on a 50 Hz
power source in the field, the H771-A supply must be replaced with an H771-C or -D (Figure 1-4) and
the drive motor belt and drive motor pulley must be replaced (Figure 1-5). The H771-C operates on a
90-120 Vac or 100-128 Vac power source. The H77I-D operates on a 184-240 Vac or 200-256 Vac
power source. To convert the H771-C to the higher voltage ranges or the H77I-D to the lower voltage
ranges, the power harness and circuit breaker must be changed. See Figure 2-3 for the appropriate
jumper and circuit breaker.

JUMPER PI

POWER PLUGS

SHIPPING
RESTRAINT (RED)
VOLTAGE (VAC)

JUMPER

CIRCUIT 8REAKER

90-120
100-128
184-240
200-256

70-10696-02
70-10696-01
70-10696-04
70-10696-03

3.5 A, 12-12301-01
3.5 A, 12-123-1·01
1.75 A, 12·12301·00
1.75 A, 12-12301·00
MA·185'5

Figure 2-3

RX02 Rear View

2.1.4 Fire and Safety Precautions
The RX02 Floppy Disk System presents no additional fire or safety hazards to an existing computer
system. Wiring should be carefully checked, however, to ensure that the capacity is adequate for the
added load and for any contemplated expansion.

2.2 CONFIGURATION GUIDELINES
The most common RX02 Floppy Disk System configurations available are listed in Table 2-1. Each
interface module listed in the table plugs into a computer bus; it is compatible with the applicable
computer so that there is adequate power to operate each module. The interconnections between each
interface module and the RX02 controller for each of the configurations in Table 2-1 is by a BCOSL-l5
cable which is 4.6 m (15 ft) maximum. (See Table 2-2 for the controller module configuration switch
positions.)

2-3

Table 2-1
Computer

PDP-8

PDP-II

LSI-II

RX02 Configurations

System
Designation

J.LCPU
Controller

Interface
Module

RX02
Model No.

Power
Supply

RX8E

M7744

M8357

RX02-BA
RX02-BC
RX02-BD

115 V, 60 Hz
115 V, 50 Hz
230 V, 50 Hz

RX28E

M7744

M8357

RX02-BA
RX02-BC
RX02-BD

115 V, 60 Hz
115 V, 50 Hz
230 V, 50 Hz

RXII

M7744

M7846

RX02-BA
RX02-BD
RX02-BD

115 V, 60 Hz
230 V, 50 Hz
230 V, 50 Hz

RX211

M7744

M8256

RX02-BA
RX02-BC
RX02-BD

115 V, 60 Hz
115V,50Hz
230 V, 50 Hz

RXVII

M7744

M7946

RX02-BA
RX02-BC
RX02-BD

115V,60Hz
115 V, 50 Hz
230 V, 50 Hz

RXV21

M7744

M8029

RX02-BA
RX02-BC
RX02-BD

115 V, 60 Hz
115 V, 50 Hz
230 V, 50 Hz

Table 2-2

Interface

Controller Configuration Switch Positions

SI-1

SI-2

rn
I

RX211, RXV21,
RX8E, RXII, RXVII,
RX28

2.3

OFF
ON
OFF

ON
OFF
OFF

c ::::J
c::::J

ON +--

SI
Top View

ENVlRONMENTAL CONSIDERATIONS

2.3.1 General
The RX02 is capable of efficient operation in computer environments; however, the parameters of the
operating environment must be determined by the most restrictive facets of the system, which in this
case are the diskettes.
2.3.2 Temperature, Relative Humidity
The operating ambient temperature range of the diskette is 15 0 to 32 0 C (59 0 to 90 0 F) with a maximum temperature gradient of 11 0 Cjhr (20 0 F jhr). The media nonoperating temperature range (storage) is increased to -34.4 0 to 51.6 0 C (-30 0 to 125 0 F), but care must be taken to ensure that the media
has stabilized within the operating temperature range before use. This range will ensure that the media
will not be operated above its absolute temperature limit of 51.6 0 C (125 0 F).

2-4

Humidity control is important in any system because static electricity can cause errors in any CPU
with memory. The RX02 is designed to operate efficiently within a relative humidity range of 20 to 80
percent, with a maximum wet bulb temperature of 25° C (77° F) and a minimum dew point of 2° C
(36° F).

2.3.3 Heat Dissipation
The heat dissipation factor for the RX02 Floppy Disk System is less than 225 Btu/hr. By adding this
figure to the total heat dissipation for the other system components and then adjusting the result to
compensate for such factors as the number of personnel, the heat radiation from adjoining areas, and
sun exposure through windows, the approximate cooling requirements for the system can be determined. It is advisable to allow a safety margin of at least 25 percent above the maximum estimated
requirements.

2.3.4 Radiated Emissions
Sources of radiation, such as FM, vehicle ignitions, and radar transmitters located close to the computer system, may affect the performance of the RX02 Floppy Disk System because of the possible
adverse effects magnetic fields can have on diskettes. A magnetic field with an intensity of 50 oersteds
or greater might destroy all or some of the information recorded on the diskette.

2.3.5 Cleanliness
Although cleanliness is important in all facets of a computer system, it is particularly important in the
case of moving magnetic media, such as the RX02. Diskettes are not sealed units and are vulnerable to
dirt. Such minute obstructions as dust specks or fingerprint smudges may cause data errors. Therefore,
the RX02 should not be subjected to unusually contaminated atmospheres, especially one with abrasive airborne particles.

NOTE
Removable media involve use, handling, and maintenance which are beyond DIGITAL's direct control.
DIGITAL disclaims responsibility for performance
of the equipment when operated with media not
meeting DIGITAL specifications or with media not
maintained in accordance with procedures approved
by DIGITAL. DIGITAL shaH not be liable for damages to the equipment or to media resulting from
such operation.

2.4

UNPACKING AND INSPECTION

2.4.1 General
The RX02 Floppy Disk System can be shipped in a cabinet as an integral part of a
separate container. If the RX02 is shipped in a cabinet, the cabinet should be positioned·
installation location before proceeding with the installation.

2-5

in a
i.~'

2.4.2 Tools
Installation of an RX02 Floppy Disk System requires no special tools or equipment. Normal hand
tools are all that are necessary. However, a forklift truck or pallet handling equipment may be needed
for receiving and installing a cabinet-mounted system.
2.4.3

Unpacking

2.4.3.1

Cabinet-Mounted

Remove the protective covering over the cabinet.

Remove the restraint on the rear door latch and open the door.

Carefully roll the cabinet off the pallet; if a forklift is available, it should be used to lift and
move the cabinet.

Remove the shipping restraint from the RX02 and save it for possible reuse.

Slide the RX02 out on the chassis slides and visually inspect for any damage as indicated in
Paragraph 2.4.3.3.

2.4.3,2 Separate Container
'1.

Open the carton (Figure 24) and remove the packing pieces.

Lift the RX02 out of the carton.

Remove the shipping fixtures from both sides of the RX02 and inspect for shipping damage
as indicated in Paragraph 2.4.3.3.

Attach the inside tracks of the chassis slides provided in the carton to the RX02 (Figure 2~ 1).

Locate the proper holes in the cabinet rails (Figure 2-5) and attach the outside tracks to the
cabinet.

Place the tracks attached to the RX02 inside the extended cabinet tracks and slide the unit in
until the tracks lock in the extended position.

Attach the front bezel with the screws supplied.

the RX02 cover in the cabinet above the unit and secure it to the cabinet rails (Figure

2-6

DISKETTES

~"""

- - ' ; - - - - - - SCO RED
SHEET

DUST
COVER

HOLDING
FIXTURE

......- - - - SCREW (8)
. . . ! , - - - REGULAR

SLOTTED
CARTON
BRACE /
WOOD

SHIPPING
CARTON

Figure 2-4

RX02 Unpacking

CP 1594

Figure 2-5

RX02 Cabinet Mounting Information

2-7

· 2.4.3.3

Inspection

Inspect the front cover(s) ofthe RX02 to be sure it operates freely. Compress the latch which
allows the spring-loaded front cover to open.

Inspect the rear of the RX02 chassis to be sure there are no broken or bent plugs. Also, be
sure the fuse is not damaged.

Visually inspect the interior of the unit for damaged wires or loose hardware.

Loosen the screws securing the hinged upper module (M7744) and raise the module so that
modules M7744 and M7745 can be inspected for damaged components or wires.

Verify that the items listed on the shipping order are included in the shipment. Be sure the
interface cable (BC05L-I5) and the appropriate interface module are included.

NOTE
If any shipping damage is found, the customer should
be notified at this time so he can contact the carrier
and record the information on the acceptance form.
2.5

INST ALLA nON
1.

Ensure that power for the system is off.

Loosen the screws securing the upper module (M7744) and swing it up on the hinge.

Inspect the wiring and connectors for proper routing and ensure that they are seated correctly.

This step is for 50 Hz versions only. Check the power configuration to ensure that the proper
jumpers and the correct circuit breaker are installed (Figure 2-3).

Connect the BC05L-i5 cable to the M7744 module and route it along the near side of the
chassis through the back of the RX02 to the CPU; then connect it to the interface module
for the PDP-8, PDP-II, or LSI-It.
The cable is connected to the M7744 module with the red stripe on the left, looking from the
component side of board; the cable is connected to the interface module with the red stripe
toward the center of the module.

Refer to Table 2-2 for the correct controller configuration switch positions.

Refer to Table 2-3 for correct device code or addressing jumpers on the interface module.

Insert the interface module into the Omnibus (PDP-8), available SPC slot (PDP-II), or LSI
bus (LSI-ll). The PDP-II and LSI-II interface modules must be inserted in the lowest
numbered available option location. Modules that use DMA processing should have a
higher priority than programmed I/O devices. For modules using DMA processing in the
PDP-II SPC slot, ensure that the NPG (NPG IN, NPG OUT) line (CAI-CBI) is cut on the
backplane.

Connect the RX02 ac power cord into a switched power source.

to.

Turn the power on, watching for head movement on the drive(s) during the power up,
initialize phase. The head(s) should move one track toward the center and back to track
zero.
2-8

Table 2-3

Interface Code/Jumper Configuration
PDP-8 (M8357)
Device Codes

670X*
671X
672X
673X
674X
67SX
676X
677X

SWI

SW2

SW3

SW4

SW5

SW6

ON
ON
ON
ON
OFF
OFF
OFF
OFF

ON
ON
OFF
OFF
ON
ON
OFF
OFF

ON
OFF
ON
OFF
ON
OFF
ON
OFF

OFF
OFF
OFF
OFF
ON
ON
ON
ON

OFF
OFF
ON
ON
OFF
OFF
ON
ON

OFF
ON
OFF
ON
OFF
ON
OFF
ON

PDP-ll (M7846) (M8256)
DR Priority

Unibus Address 17717X*

BR7 - S4-0S7S2
BR6 - 54-0S7S0
BRS - S4-0S77S*
BR4 - S7-0S776

AI2/WIS - Removed
AII/WI7 - Removed
AIO/WI6 - Removed
A9/WIS - Removed
AS/WI4 -Installed
A 7/W13 -Installed
A6/W12 - Removed
AS/WI I - Removed
A4/WIO - Removed
A3/W9 - Removed

Vector Address (264.)*
SWIO OFF
SW9 OFF
SW8 OFF
SW7 OFF
SW6 ON
SW5 ON
SW4 OFF
SW3 OFF
SW2 OFF
SWIOFF

SWION
SW20FF
SW30N
SW40N
SWS OFF
SW60N
SW70FF

V2/WI -Installed
V3/W2 - Removed
V4/W3 - Installed
VS/W4-lnstalled
V6/WS - Removed
V7/W6 - Installed
VS/W7 - Removed

LSI-ll
(M8029)

(M7946)
Register Address·
(I 77 17X.)

A-I - CPU Selectable
W-7/ A-2 - Installed
W-S/A-3 - Removed
W-9/ A-4 - Removed
W-IO/A-S - Removed
W-II/ A-6 - Removed
W-12/A-7 -Installed
W-13/A-S- Installed
W-14/ A-9 - Removed
W-IS/A-IO- Removed
W-16/A-ll -Removed
W-17/A-12- Removed

Vector Address·
(264.)

Vector Address*
(264,)

W-I/V-2 - Removed
W-2/V-3 - Installed
W-3/V-4 - Removed
W-4/V-S - Removed
W-S/V-6 -Installed
W-6/V-7 - Removed

A-I - CPU Selectable
A-2 - Hardwired
A-3 -Installed
A-4 - Installed
A-S - Installed
A-6 - Installed
A-7 - Removed
A-S Removed
A-9 -Installed
A-IO - Installed
A-II - Installed
A-12 - Installed

V2 -Installed
V-3 - Removed
V-4 - Installed
V-5 -Installed
V-6- Removed
V-7 -Installed
V-S - Removed

*Standard

2-9

.2.5.1 PDPS-A Modification
In order to bootload from an RX02 on a PDP8-A system, it is necessary to modify the KM8-A
(M8317) extended option module (if present) as follows (Figure 2-6):
• replace E82 with prom #23-465A2
• replace E87 with prom #23-469A2
• set SW#l and SW#2 according to the bootload device as shown below.
Program

S2-5

S2-6

S2-7

S2-8

SI-I

SI-2

SI-3

H/L PTR
RK8-E
RX8-E
RL8A

ON
ON
ON
OFF

ON
OFF
OFF
ON

ON
ON
OFF
OFF

OFF
OFF
ON
OFF

ON
ON
OFF
OFF

ON
OFF
ON
ON

ON
ON
ON
OFF

51-8

::~
MA-2'109

Figure 2-6

KM8-A Modification

2.6 TESTING
To test the operation of RX02, run the DEC diagnostics supplied. Perform the diagnostics in the
sequence listed for the number of passes (time) indicated.
RX8 or RX 11 Diagnostic - 2 passes
Data Reliability jExerciser - 3 passes
DECX-8 or DECX-II - 10 minutes
If any errors occur contact Field Service.

2-10

CHAPTER 3
USER INFORMATION

3.1 CUSTOMER RESPONSIBILITY
It is the user's responsibility to ensure that the RX02 is located and operated in an area that is free
from excessive dust and dirt, and meets or exceeds the environmental conditions listed in Paragraph
1.4. The exterior of the RX02 should be kept clean. Also, it is the user's responsibility to ensure that
the diskettes are handled and stored properly in order to prevent errors or data loss which might occur
when recording or reading data; diskette handling procedures are described in Paragraph 3.2.

3.2

CARE OF MEDIA

3.2.1 Handling Practices and Precautions
To prolong the diskette life and prevent errors when recording or reading, reasonable care should be
taken when handling the media. The following handling recommendations should be followed to
prevent unnecessary loss of data or interruptions of system operation.
I.

Do not write on the envelope containing the diskette. Write any information on a label prior
to affixing it to the diskette.

Paper clips should not be used on the diskette.

Do not use writing instruments that leave flakes, such as lead or grease pencils, on the jacket
of the media.

Do not touch the disk surface exposed in the diskette slot or index hole.

Do not clean the disk in any manner.

Keep the diskette away from magnets or tools that may have become magnetized. Any disk
exposed to a magnetic field may lose information.

Do not expose the diskette to a heat source or sunlight.

Always return the diskette to the envelope supplied with it to protect the disk from dust and
dirt. Diskettes not being used should be stored in a file box if possible.

When the diskette is in use, protect the empty envelope from liquids, dust, and metallic
materials.

10.

Do not place heavy items on the diskette.

3-1

II.

Do not store diskettes on top of computer cabinets or in places where dirt can be blown by
fans into the diskette interior.

12.

If a diskette has been exposed to temperatures outside the operating range, allow five minutes for thermal stabilization before use. The diskette should be removed from its packaging
during this time.
CAUTION
• Do not use paper clips on diskettes.
• Do not expose the diskette to a heat source or sunlight.
• Keep the diskettes from magnetic fields.
• Do not write on the diskette with an instrument
that leaves an impression or flakes.

3.2.2

Diskette Storage

3.2.2.1

Short Term (Available for Immediate Use)

Store diskettes in their envelopes.

Store horizontally, in piles of ten or less. If vertical storage is necessary, the diskettes should
be supported so that they do not lean or sag, but should not be subjected to compressive
forces. Permanent deformation may result from improper storage.

Store in an environment similar to that of the operating system; at a minimum, store within
the operating environment range.

3.2.2.2 Long Term - When diskettes do not need to be available for immediate use, they should be
stored in their original shipping containers within the nonoperating range of the media.

3.2.3 Shipping Diskettes
Data recorded on disks may be degraded by exposure to any sort of small magnet brought into close
contact with the disk surface. If diskettes are to be shipped in the cargo hold of an aircraft, take
precautions against possible exposure to magnetic sources. Because physical separation from the magnetic source is the best protection against accidental erasure of a diskette, diskettes should be packed at
least 3 inches within the outer box. This separation should be adequate to protect against any magnetic
sources likely to be encountered during transportation, making it generally unnecessary to ship diskettes in specially shielded boxes.
When shipping, be sure to label the package:
DO NOT EXPOSE TO PROLONGED HEAT OR SUNLIGHT.

When received, the carton should be examined for damage. Deformation of the carton should alert the
receiver to possible damage of the diskette. The carton should be retained, if it is intact, for storage of
the diskette or for future shipping.

3-2

3.3

OPERATING INSTRUCTIONS

NOTE
The left drive is always identified as drive O.

The RX02 has no operator controls and indicators. The diskette is inserted on a drive after compressing the latch to allow the spring-loaded front cover to open. Place the diskette with the label or
top up (the jacket seams are on the bottom) on the drive spindle. Close the front cover which will
automatically lock when it is pushed down. Initialize the system (from the computer) and listen for
audible clicking sounds which indicate the head is moving over the diskette; the RX02 is ready for use.
Data storage and retrieval is controlled by the user's program.

CAUTION
Do not open the drive door while the diskette is in
use; this results in errors.

3.4 OPERATOR TROUBLESHOOTING
Table 3-\ is a list of possible problems and some probable causes the operator may encounter. If the
problem cannot be corrected, refer to the RX02 Floppy Disk System Technical Manual if available.

Table 3-1

Operator Troubleshooting Guide
Correction

Problem

Probable Cause

No power
(drive inoperative)

a.
b.
c.

Power cord disconnected
Blown fuse
Circuit breaker open

a.
b.
c.

Connect power cord
Replace fuse
Close circuit breaker

Drive not ready

a.
b.

Drive door open
Diskette improperly installed

a.
b.

Close door
Properly seat diskette

Error in recording

a.
b.

Diskette wear
Diskette mounting hole

a.
b.

Mismatch in recording density
on a diskette

If worn, replace
If the hole is not concentric. replace diskette
If diskette data density is not
compatible with data to be recorded. replace diskette with a
new preformatted diskette.

3-3

CHAPTER 4
PROGRAMMING

This chapter contains programming information for the following interface options: RX8E, RX28,
RXII, RXVII, RX211, and RXV21. The RX8E and RX28 programming information is presented
followed by the RXII and RXVII information and then the RX211 and RXV21 information is presented. The RX8E, RX 11, and RXVII options are used for single density recording and are compatible with the RXOI Floppy Disk System. The RX28E, RX211, and RXV21 can be used for either
single or double density recording.

4.1 RX8E AND RX28 PROGRAMMING INFORMATION
The RX8E interface allows two modes of data transfer: 8-bit word length and 12-bit word length. In
the 12-bit mode, 64 words are written in a diskette sector, thus requiring 2 sectors to store I page of
information. The diskette capacity in this mode is 128,128 12-bit words (1001 pages). In the 8-bit
transfer mode, 128 8-bit words are written in each sector. Disk capacity is 256,256 8-bit words, which is
a 33 percent increase in disk capacity over the 12-bit mode. The 8-bit mode must be used for generating
IBM-compatible diskettes, since 12-bit mode does not fully pack the sectors with data. The hardware
puts in the extra Os. Data transfer requests occur 23 ms after the previous request was serviced for 12bit mode (18 ms for 8-bit mode). There is no maximum time between the transfer request from the
RX02 and servicing of that request by the host processor. This allows the data transfer to and from the
RX02 to be interrupted without loss of data.
The RX28 interface allows two modes of data transfer: 8-bit word length and 12-bit word length. For
each mode of data transfer there can be either single density or double density storage of data. In the
12-bit mode single density recording, 64 words are written in a diskette sector, and the diskette capacity is 128,128 12-bit words; for double density, there are 128 words written in a sector with a diskette
capacity of 256,256 12-bit words. In the 8-bit word mode single density recording, 128 8-bit bytes are
written in each sector and the diskette capacity is 256,256 8-bit bytes; for double density, there are 256
8-bit bytes written in a sector with a diskette capacity of 512,512 8-bit bytes. (For the 12-bit mode, all
12-bit data words are loaded into the buffer and then the hardware forces zeros to add extra bits to the
end of the buffer so that the buffer is filled.)

4.1.1 Device Codes
The eight possible device codes that can be assigned to the interface are 70-77. These device codes
define address locations of a specific device and allow up to eight RX8EjRX28 interfaces to be used on
a single PDP-8. These multiple device codes are also shared with other devices. Depending on what
other devices are on the system, the RX8EjRX28 device code can be selected to avoid conflicts. (Refer
to the PDP-8 Small Computer Handbook for specific device codes.)

4-1

The device codes are selected by switches according to Table 4-1. These switches control ac bits 6-8,
while ac bits 3-5 are fixed at Is. The device code is initially selected to be 70. Switches 7 and 8 are not
connected and will not affect the device selection code. The switches are all located on a single DIP
switch package that is located on the M8357 RX8EjRX28 interface board.

Table 4-1
Device
Code

Device Code Switch Selection

0
0
0
0

0
0

1
1

0
0

1
I

71
70

I
I

I
1

76
75
74
73

1
1
I

S4
1
1
1
1

0
0
0
0

S5
1
1

S6
1

0
0

1
1

0
0

S7
X
X
X
X
X
X
X
X

S8
X
X
X
X
X
X
X
X

o(OFF)

1 (ON)

c:=:J
c:=:J

SI
S2
S3
S4
S5
S6
S7
S8

c:=:::::J
I

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

c:=:J
c:::::::::J

4.1.2 Instruction Set
The RX8EjRX28 instruction set is listed below and described in the following paragraphs. When
operating as an RX28, for the 8-bit mode, all instruction set commands are transferred in two 8-bit
bytes .
. IOT

Mnemonic

Description

67xO
67xl
67x2
67x3
67x4
67x5
67x6
67x7

LCD
XDR
STR
SER
SDN
INTR
INIT

No Operation
Load Command, Clear AC
Transfer Data Register
Skip on Transfer Request Flag, Clear Flag
Skip on Error Flag, Clear Flag
Skip on Done Flag, Clear Flag
Enable or Disable Disk Interrupts
Initialize Controller and Interface

4.1.2.1 RX8E Load Command (LCD) - 67x1 - This command transfers the contents of the AC to the
interface register and clears the AC. The RX02 begins to execute the function specified in AC 8,9, and
to on the drive specified by AC 7. A new function cannot be initiated unless the RX02 has completed
the previous function. The command word is defined as shown in Figure 4-1. The command word is
described in greater detail in Paragraph 4.1.3.1.

I \

S/12 \

'-----.,.,------" I
NOT USED

MAINT

I~::I FUNCTION I I

NOT
USED

NOT
USED
MA,18S3

Figure 4-1

LCD Word Format (RX8E)

4-2

4.1.2.2 RX28 Load Command - (First byte 67x1, second byte - 67x2) - This command transfers the
contents of the AC to the interface register and clears the AC. The RX02 begins to execute the function
specified in AC 8, 9, and 10 on the drive specified by AC 7. A new function cannot be initiated unless
the RX02 has completed the previous function. The command word is defined as shown in Figure 4-2
and is described in greater detail in Paragraph 4.1.3.1.

12 BIT
MODE
'---.,---.J'

I I

FUNCTION

i
UNIT

NOT RESERVED MAI~JT
USED

SEL

TRANSFER 6701
BYTE 1
SBJT {
MODE

TR ANSF E R
BYTE 2
6702 {XDRI

r-..---.--r---r--r-.--.---.

00.03

0
~~~--~~~--~~~

Figure 4-2

Command Word Format (RX28)

When operating in the 8-bit mode, the Load command is stored in two 8-bit transfers. The first 8 bits
of the command word (shown as bits 4-11 in Figure 4-2) are stored; then TR is asserted and an XDR is
performed to transfer the remaining bits of data (bit 3, DEN, and bit 2, as shown in Figure 4-2) rightjustified. The extra bits in the second 8-bit transfer are filled with zeros. Upon completing the transfer
of the second 8-bit byte, Done is asserted to end the function.
4.1.2.3 Transfer Data Register (XDR) - 67x2 - With the maintenance flip-flop cleared, this instruction operates as follows. A word is transferred between the AC and the interface register. The direction
of transfer is governed by the RX02 and the length of the word transferred is governed by the mode
selected (8-bit or 12-bit). When Done is negated, executing this instruction indicates to the RX02 that:
I.

The last data word supplied by the RX02 has been accepted by the PDP-8, and the RX02
can proceed, or

The data or address word requested by the RX02 has been provided by the PDP-8, and the
RX02 can proceed.

A data transfer (X DR) from the AC always leaves the AC unchanged. If operation is in 8-bit mode,
AC 0-3 are transferred to the interface register but are ignored by the RX02. Transfers into the AC are
12-bit jam transfers when in 12-bit mode. When in 8-bit mode, the 8-bit word is ORed into AC 4-11
and AC 0-3 remain unchanged. When the RX02 is done, this instruction can be used to transfer the
RXES status word from the interface register to the AC. The selected mode controls this transfer as
indicated above.
4.1.2.4 STR - 67x3 - This instruction causes the next instruction to be skipped if the transfer request
(TR) flag has been set by RX02 and clears the flag. The TR flag should be tested prior to trarhferring
data or address words with the XDR instruction to ensure the data or address has been received or
transferred, or after an LCD instruction to ensure the command is in the interface register. I n cases
where an XDR follows an LCD, the TR flag needs to be tested only once between the two instructions.

4-3

4.1.2.5 . SER - 67x4 - This instruction causes the next instruction to be skipped if the error flag has
been set by an error condition in the RX02 and clears the flag. An error also causes the done flag to be
set (Paragraph 4.1.3.6).
4.1.2.6 SDN - 67x5 - This instruction causes the next instruction to be skipped if the done flag has
been set by the RX02, indicating the completion of a function or detection of an error condition. If the
done flag is set, it is cleared by the SON instruction. This flag will interrupt ifinterrupts are enabled.
4.1.2.7 INTR - 67x6 - This instruction enables interrupts by the done flag if AC 11 = 1. It disables
interrupts if AC 11 =0.
4.1.2.8 INIT - 67x7 - The instruction initializes the RX02 by moving the head position mechanism of
drive 1 (if drive I is available) to track O. It reads track 1, sector I of drive O. It zeros the error and
status register and sets Done upon successful completion of Initialize. Up to 1.8 seconds may elapse
before the RX02 returns to the Done state. Initialize can be generated by the program or by the
Omnibus Initialize.
4.1.3 Register Description
Only one physical register (the interface register) exists in the RX8EjRX28, but it may represent one of
the six RX02 registers described in the following paragraphs, according to the protocol of the function
In progress.
4.1.3.1 Command Register (Figures 4-3 and 4-4) - The command is loaded into the interface register
by the LCD instruction for RX8E and by a load command (LCD and XDR) for the RX28 (Paragraphs 4.1.2.1 and 4.1.2.2).

FUNCTION

' - - - - v .-~,
MAINT
NOT USED

NOT
USED

I I
NOT
USED
Mi\ 17')3

Figure 4-3

00
12 BIT MO D E

Command Register Format (RX8E)

1.....--L1D_EN....l..I-,-LI_811....J21-r-.L...1-r-!..1..-FU_N_CT_IO_N-1.1-,--11
11...-.1...-...1...
, . !I
I
I C:: UNIT
I
NOT RESERVED MAINT
USED

NOT USED

SEL

NOT USED

1ST BYTE

" " MOOC {
2ND BYTE

•

NOT USED

Figure 4-4

Command Register Format (RX28)

4-4

The function codes (bits 8, 9, 10) are summarized below and described in Paragraph 4.1.4.
Code

Function

000
001
010
011
100
101
110
I II

Fill Buffer
Empty Buffer
Write Sector
Read Sector
Not used (RX8E) - Set Density (RX28)
Read Status
Write Deleted Data Sector
Read Error Register

The DRY (UNIT) SEL bit (bit 7) selects one of the two drives upon which the function will be
performed:
AC7 =0
AC7=1

Select drive 0
Select drive 1

The 8/12 bit (bit 5) selects the length of the data word.
AC5=0
AC 5 = I

12-bit mode selected
8-bit mode selected

The DEN bit (bit 3) for RX28 indicates the density for the function to be performed (0 = single, 1 =
double). The RX8E/RX28 will initialize into 12-bit mode.
4.1.3.2 Error Code Register (Figure 4-5) - Specific error codes can be accessed by use of the read error
code function (111) (Paragraph 4.1.4.9). The specific octal error codes are given in Paragraph 4: 1.5.

' - - - - _ - . , - - -_ _'

_ _ _ __ . . ._ _ _ _ _.J

ERROR CODE

NOT USED

CP '515

Figure 4-5

Error Code Register Format (RX8E/RX28A)

The maintenance bit (M bit) can be used to diagnose the RX8E interface under off-line and on-line
conditions. The off-line condition exists when the BC05L-15 cable is disconnected from the RX02; the
on-line condition exists when the cable is connected to the RX02.
If an LCD lOT (I/O transfer) is issued with AC 4 = 1, the maintenance flip-flop is set. When the
maintenance flip-flop is set, the assertion of RUN following XDR instructions is inhibited, and all
data register transfers (XDR) are forced into the AC. The maintenance bit allows the interface register
to be written and read for maintenance checks. The maintenance flip-flop is cleared by Initialize or by
a Load Command lOT with AC 4 = O. The following paragraphs describe more explicitly how to use
the maintenance bit in an off-line mode.
The contents of the interface buffer cannot be guaranteed immediately following the first Load Command lOT, which sets the maintenance flip-flop. However, successive Load Command lOTs will guarantee the contents of the interface register. The contents of the interface register can then be verified by
using the XDR lOT to transfer those contents into the AC.

4-5

In addition, the maintenance flip-flop directly sets the skip flags, which will remain set as long as the
maintenance flip-flop is set. Skipping on these flags as long as the maintenance flip-flop is set will not
clear the flags. Setting and then clearing the maintenance flip-flop will leave the skip flags in a set
condition. The skip lOTs can then be issued to determine whether or not a large portion of the
interface skip logic is working correctly.
With the maintenance flip-flop set, it can be determined if the interface is capable of generating an
interrupt on the Omnibus. When the maintenance flip-flop is set, the done flag is set, and the interrupt
enable flip-flop can be set by issuing an INTR lOT with AC bit II =1. The combination of done and
interrupt enable should generate an interrupt.
The maintenance flip-flop can also be used to test the INIT lOT. The maintenance flip-flop is set and
cleared to generate the flags, and INIT lOT is then executed. If execution of INIT lOT is internally
successful, all of the flags and the interrupt enable flip-flop should be cleared if they were previously
set.
In the on-line mode, use of the maintenance bit should be restricted to writing and reading the interface register. The same procedure described to write and read the interface register in the off-line mode
should be implemented in the on-line mode. Exiting from the on-line maintenance bit mode should be
finalized by an initialize to the RX02.
4.1.3.3 RXlTA - RX Track Address (Figure 4-6) - This register is loaded to indicate on which of the
77 (0-76) tracks a given function is to operate. It can be addressed only under the protocol of the
function in progress (Paragraph 4.1.4). Bits 0-3 are unused and are ignored by the control.
4.1.3.4 RXlSA - RX Sedor Address (Figure 4-7) - This register is loaded to indicate on which of the
26 (1-26) sectors a given function is to operate. It can be addressed only under the protocol of the
function in progress (Paragraph 4.1.4). Bits 0-3 are unused and are ignored by the control.
4.1.3.5 RX2DB - RX Data Buffer (Figure 4-8) - All information transferred to and from the floppy
media passes through this register and is addressable only under the protocol of the function in progress. The length of data transfer is either 8 or 12 bits, depending on the state of bit 5 of the command
register when the Load Command lOT is issued (Paragraph 4.1.3.1).
4.1.3.6 RX8E - RX Error and Status (Figure 4-9) - The RXES contains the current error and status
conditions of the selected drive. This read-only register can be accessed by the read status function
(10 1). The RXES is also available in the interface register upon completion of any function. The RX ES
is accessed by the XDR instruction. The meaning of the error bits is given below.
00

I I , I I Ia I I
0

0·114,

I I I

NOT USED

1·32,
MA 1859

Figure 4-6

I I.

NOT
USED

RX2TA Format (RX8EjRX28)

Figure 4-7

RX2SA Format (RX8EjRX28)

I~~~I DO I

I I ICRCI
ID

12 81T

8 OR 12 BIT

MODE ONLY

MODE

Figure 4-8

RX2DB Format (RX8EjRX28)

NOT USED

MA-1860

MA 1861

Figure 4-9

4-6

RXES Format (RX8E)

Bit No.

Description

eRe Error - The cyclic redundancy check at the end of the data field has indicated an error.
The data must be considered invalid; it is suggested that the data transfer be retried up to to
times, as most data errors are recoverable (soft).

Initialize Done - This bit indicates completion of the Initialize routine. It can be asserted
due to RX02 power failure, system power failure, or programmable or bus Initialize. This
bit is not available within the RXES from a read status function.

Deleted Data (DO) - In the course of reading data, a deleted data mark was detected in the
identification field. The data following will be collected and transferred normally as the
deleted data mark has no further significance within the RX02. Any alteration of files or
actual deletion of data due t9 this mark must be accomplished by user software. This bit will
be set if a successful or unsuccesful Write Deleted Data function is performed.

Drive Ready - This bit is asserted if the unit currently selected exists, is properly supplied
with power, has a diskette installed properly, has its door closed, and has a diskette up to
speed.
NOTE 1
This bit is only valid for either drive when retrieved
via a Read Status function or for drive 0 upon completion of an Initialize.
NOTE 2
If the error bit was set in the RX2CS but error bits
are not set in the RXES, specific err.or conditions can
be accessed via a read error register function.

4.1.3.7 RX28 - RX Error and Status (Figure 4-10) - The RX2ES contains the current error and status
conditions of the selected drive. This read-only register can be accessed by the read status function
(101). The RX2ES is also available in the interface register upon completion of any function. The
RX2ES is accessed by the XDR instruction. The meaning of the error bits is given below.

[

I~~~I DO Ig~~I~~~1

110 I ICRCI

RX02

NOT USED

Figure 4-10

RX2ES Format (RX28)

Bit No.

Description

Reserved.

Bit No.

Description

RX02 - This bit is asserted if an RX02 system is being used.

DEN ERR - This bit indicates that the density of the function does not agree with the drive
density. Upon detection of this error the control terminates the operation and asserts error
and done.

DRV DEN - This bit indicates the density of the diskette in the drive selected (0 = single, 1
= double).

Deleted Data (DD) - In the course of reading data, a deleted data mark was detected in the
identification field. The data following will be collected and transferred normally, as the
deleted data mark has no further significance within the RX02. Any alteration of files or
actual deletion of data due to this mark must be accomplished by user software. This bit will
be set if a successful or unsuccessful write deleted data function is performed.

-4

Drive Ready - This bit is asserted if the unit currently selected exists, is properly supplied
with power, has a diskette installed properly, has its door closed, and has a diskette up to
speed.
NOTE 1
This bit is only valid for either drive when retrieved
via a read status function or for drive 0 upon completion of an Initialize.
NOTE 2
If the error bit was set in the RX2CS but error bits
are not set in the RX2ES, specific error conditions
can be accessed via a read error code function.

4.1.4 Function Code Description
The RX8E/RX28 functions are initiated by means of the Load command described in Paragraphs
4.1.2.1 and 4.1.2.2. The done flag should be tested and cleared with the SDN instruction in order to
verify that the RX8E/RX28 is in the Done state prior to issuing the command instruction. Upon
receiving a command instruction while in the Done state, the RX8E/RX28 enters the Not Done state
while the command is decoded. Each of the eight functions summarized below requires that a strict
protocol be followed for the successful transfer of data, status, and address information. The protocol
for each function is described in the following sections. A summary table is presented below.
AC
Octal 8

Function

0
2
4
6

0
0
0
0

0
0

1
1

I
I
I

0
0

1
1

Fill Buffer
Empty Buffer
Write Sector
Read Sector
Not Used (RX8E), Set Density (RX28)
Read Status
Write Deleted Data Sector
Read Error Register

12
14
16

1
1
I
1

NOTE
AC bit 11 is assumed to be 0 in the above octal codes
since AC bit 11 can be 0 or 1.
4-8

4.1.4.1 Fill Buffer (000) - For RX8E this function is used to load the RX02 sector buffer from the
host processor with 64 12-bit words ifin 12-bit mode or 128 8-bit words ifin 8-bit mode. For RX28 this
function loads the sector buffer in 12-bit mode with 64 12-bit words for single density or 128 12-bit
words for double density; in the 8-bit mode, the buffer is loaded with 128 8-bit bytes for single density
or 256 8-bit bytes for double density. This instruction only loads the sector buffer. In order to complete
the transfer to the diskette, another function, write sector, must be performed. The buffer may also be
read back by means of the empty buffer function in order to verify the data.
Upon decoding the fill buffer function, the RX02 will set the transfer request (TR) flag, signaling a
request for the first data word. The TR flag must be tested and cleared by the host processor with the
STR instructions prior to each successive XDR lOT (Paragraph 4.1.2.4). The data word can then be
transferred to the interface register by means of the XDR lOT. The RX02 next moves the data word
from the interface register to the sector buffer and sets the TR flag as a request for the next data word.
The sequence above is repeated, until the sector buffer has been loaded (64 data transfers for 12-bit
mode or 128 data transfers for 8-bit mode). After the 64th (or 128th) word has been loaded into the
sector buffer. the RX2ES is moved to the interface register, and the RX02 sets the done flag to indicate
the completion of the function. Therefore. it is unnecessary for the host processor to keep a count of
the data transfers. Any XDR commands after Done is set will result in the RX2ES status word being
loaded in the AC. The sector buffer must be completely loaded before the RX8E/RX28 will set Done
and recognize a new command. An interrupt would now occur if Interrupt Enable were set.

4.1.4.1 Empty Buffer (001) - This function moves the contents of the sector buffer to the host processor. Upon decoding this function RX2ES bits are cleared and the TR flag is set with the first data word
in the interface register. This TR flag signifies the request for a data transfer from the RX8E/RX28 to
the host processor. The flag must be tested and cleared; then the word can be moved to the AC by an
XDR command. The direction of transfer· for an XDR command is controlled by the RX02. The TR
flag is set again with the next word in the interface register. The above sequence is repeated until all
words or bytes have been transferred, thus emptying the sector buffer. The done flag is then set after
the RX2ES is moved in the interface register to indicate the end of the function. An interrupt would
now occur if Interrupt Enable were set.
NOTE
The empty buffer fundion does not destroy the contents of the sector buffer.

4.1.4.3 Write Sector (010) - This function transfers the contents of the sector buffer to a specific track
and sector on the diskette. Upon decoding this function. the RX8E/RX28 clears the RX2ES and sets
the TR flag. signifying a request for the sector address. The TR flag must be tested and cleared before
the binary sector address can be loaded into the interface register by means of the XD R command. The
sector address must be within the limits 1-328.
The TR flag is set, signifying a request for the track address. The TR flag must be tested and cleared;
then the binary track address may be loaded into the interface register by means of the XDR command. The track address must be within the limits 0-1148.
The RX02 tests the supplied track address to determine if it is within the allowable limits. If it is not.
the RX2ES is moved to the interface register, the error and done flags are set, and the function is
terminated.

4-9

If the track address is legal, the RX02 moves the head of the selected drive to the selected track, locates
the requested sector, transfers the contents of the sector buffer and a CRC character to that sector, and
sets Done. Any errors encountered in the seek operation will cause the function to cease, the RX2ES to
be loaded into the interface register, and the error and done flags to be set. If no errors are encountered, the RX2ES is loaded into the interface register and only the done flag is set.
NOTE
The write sector function does not destroy the contents of the sector buffer.
4.1.4.4 Read Sector (OU) - This function moves a sector of data from a specified track and sector to
the sector buffer. Upon decoding this function, the RX8EjRX28 clears RX2ES and sets the TR flag,
signifying the request for the sector address. The flag must be tested and cleared. The sector address is
then loaded into the interface register by means of the XD R command. The TR flag is set, signifying a
request for the track address. The flag is tested and cleared by the host processor and the track address
is then loaded into the interface register by an XDR command. The legality of the track address is
checked by the RX02. If illegal, the error and done flags are set with the RX2ES moved to the interface
register and the function is terminated. Otherwise, the RX02 moves the head to the specified track,
locates the specified sector, transfers the data to the sector buffer, computes and checks CRC for the
data. If no errors occur, the done flag is set with the RX2ES in the interface register. If an error occurs
anytime during the execution of the function, the function is terminated by setting the error and done
flags with RX2ES in the interface register. A detection of CRC error results in RX2ES bit 11 being set.
If a deleted data mark was encountered at the beginning of the desired data field, RX2 ES bit 5 is set.
4.1.4.5 Set Media Density (100) for RX28 only - This function causes the entire diskette to be reassigned to a new density. The density bit (bit 3 RX2CS) indicates the new density of the diskette. The
control reformats the diskette by writing new data address marks (double or single density) and zeroing 'out all data fields on the diskette. Before executing the command the control will look for a
protective key word of 01001001 (ASCII'!').
The control starts at sector 1, track 0 and reads the header information, then starts a write operation,
writing the new data address mark and data field as well as CRC characters. If the header information
is damaged, the control will abort the operation and assert DONE and ERROR.
This operation takes about 15 seconds and should not be interrupted. If for any reason the operation is
interrupted, an illegal diskette has been generated which may have data marks of both densities. This
diskette should again be completely reformatted.
4.1.4.6 Maintenance Read Status (101) for RX28 only - This function updates the drive ready and
drive density status of the selected drive, clears the INIT DONE bit, updates the Unit Sel, possibly sets
the density error bit and leaves the remainder of the RX2ES unchanged. The drive density is updated
by loading the head on the selected drive (without changing head and reading position) with the first
header and data mark that randomly appears under the head. The control will then generate the
appropriate number of shift pulses which will transfer the RX2ES (error and status) register over the
interface. Upon completion of the RX2ES transfer, the control asserts Done to complete the operation.
4.1.4.7 Read Status (l01) for RX8E only - Upon decoding this function, the RX02 moves the RXES
to the RX8E interface register and sets the done flag. The RXES can then be read by the transfer data
register (XD R) command. The bits are defined in Paragraph 4.1.3.6.
NOTE
The average time for this function is 250 ms. Excessive use of this function will result in substantially
reduced throughput.
4-10

4.1.4.8 Write Deleted Data Sector (110) - This function is identical to the write data function except
that a deleted data mark is written prior to the data field rather than the normal data mark (Paragraph
1.5.3.2). RX2ES bit 5 (Deleted Data) will be set in the interface register upon completion of the
function.

4.1.4.9 Read Error Code Function (111) - The read error code function can be used to retrieve explicit
error information upon detection of the error flag. Upon receiving this function, the RX02 moves an
error code to the interface register and sets Done. The interface register can then be read via an XD R
command and the code interrogated to determine which type of failure occurred (Paragraph 4.1.5).
NOTE
Care should be exercised in the use of this function.
The program must perform this function before a
read status because the error register is always modified by a read status function.

4.1.4.10 Power Fail - There is no actual function code associated with power fail. When the RX02
senses a loss of power, it will unload the head and abort all controller action. All status signals are
invalid while power is low.
When the RX02 senses the return of power, it will remove Done and begin a sequence to:
1.
2.
3.
4.

Move drive I head position mechanism to track O.
Clear any active error bits.
Read sector I of track 1 of drive 0 into the buffer.
Set Initialize Done bit of the RX2ES, after which Done is again asserted.

There is no guarantee that information being written at the time of a power failure will be retrievable.
However, all other information on the diskette will remain unaltered.
INIT lOT is a method of aborting an incomplete function (Paragraph 4.1.2.7).

4.1.5

Error Recovery

4.1.5.1 RX8E - There are two error indications given by the RX8E system. The read status function
(Paragraph 4.1.4.7) will assemble the current contents ofthe RXES (Paragraph 4.1.3.6), which can be
sampled to determine errors. The read error register function (Paragraph 4.1.4.9) can also be used to
retrieve explicit error information.
The results of the read status function or the read error register function are in the interface register
when Done sets, indicating the completion of the function. The XDR lOT must be issued to transfer
the contents of the interface register to the PDP-8's AC.
NOTE
A read status function is not necessary if the D RV
READY bit is not going to be interrogated because
the RXES is in the interface register at the completion of every function.
4-11

The error codes for the read error register function are presented below.
OCtal
Code

Error Code Meaning

0010
0020
0030
0040
0050
0070
0110
0120
0130
0150
0160
0170
0200
. 0210
0220
0240

Drive 0 failed to see home on Initialize.
Drive I failed to see home on Initialize.
Found home when stepping out 10 tracks for INIT
Tried to access a track greater than 77
Home was found before desired track was reached
Desired sector could not be found after looking at 52 headers (2 revolutions)
More than 40 J.LS and no SEP clock seen
A preamble could not be found.
Preamble found but no I/O mark found within allowable time span
The header track address of a good header does not compare with the desired track.
Too many tries for an IDAM (identifies header)
Data A M not found in allotted time
eRe error on reading the sector from the disk. No code appears in the ERREG .
All parity errors
Self diagnostic error on Initialize
Density Error

4.1.5.2 RX28 - There are two error indications given by the RX28 system. The read status function
will assemble the current contents of the RX2ES which can be sampled to determine errors. The read
error register function can also be used to retrieve explicit error information.
The results of the read status function or the read error register function are in the interface register
when Done sets, indicating the completion of the function. The XDR lOT must be issued to transfer
the contents of the interface register to the PDP-8's AC.
NOTE
A read status function is not necessary if the DRV
RDY bit is not going to be interrogated because the
RX2ES is in the interface register at the completion
of every function.
The error codes for the read error register function are presented below.
Octal
Code

Error Code Meaning

0010
0020
0040
0050
0070
0110
0120
0130
0150
0160
0170
0200
0220
0240
0250

Drive 0 failed to see home on Initialize.
Drive I failed to see home on Initialize.
Tried to access a track greater than 76
Home was found before desired track was reached.
Desired sector could not be found after looking at 52 headers (2 revolutions).
More than 40 J.LS and no SEP clock seen
A preamble could not be found.
Preamble found but no ID mark found within allowable time span
The header track address of a good header does not compare with the desired track.
Too many tries for an IDAM (identifies header)
Data AM not found in allotted time
eRe error on reading the sector from the disk
R/W electronics failed maintenance mode test.
Density error
Wrong key word for Set Media Density command
4-12

4.1.6 RX8E Programming Examples

4.1.6.1 Write/Write Deleted Data/Read Functions - Figure 4-11 presents a program for implementing a write, write deleted data, or a read function with interrupts turned off (lOF). The first 3 steps
preset the PTRY, CTRY, and STRY retry counters, which are set at 10 retries but can be changed to
any number. Starting at RETRY, the program tests for 8- or 12-bit mode, type of function, and drive.
Once the command is loaded, the program waits in a loop for the controller to respond with transfer
request (TR). When TR is set, the sector address is loaded and the AC is cleared. The program loops
while waiting for the controller to respond with another TR. When TR is reset, the track address is
loaded and the AC is cleared again. The program loops to wait for the Done condition.

When the done flag is set, the program checks for an error condition, indicated by the error flag being
set. If the AC=OOOO, the error is a seek error; if bit 11 of the AC is set, the error is a CRC error. Error
status from the RXES is saved and tested to determine the error (Paragraph 4.1.3.6). The RXES will
not include the select drive ready bit. If a parity error is detected, the program increments and tests the
PTRY retry counter. If a parity error persists after 10 tries, it is considered a hard error. If 10 retries
have not occurred, a branch is made to RETRY and the sequence is repeated.

After a parity test, the program tests to see if the CRC error bit is set. If a CRC error is detected, the
program increments and tests the CTRY retry counter. If a CRC error persists after 10 retries, it is
considered a hard error. If to retries have not occurred, a branch is made to RETRY and the sequence
repeated.

A seek error is assumed if neither a CRC nor a parity error is detected. An Initialize (IN IT) instruction
is performed (Paragraph 4.1.2.8). During a write or write deleted data function, the sector buffer must
be refilled because INIT will cause sector I of track I of drive 0 to be read, which will destroy the
previous contents of the sector buffer. The instruction sequence for a fill buffer function is not included
in Figure 4-11, but is presented in Figure 4-13. After the system has been initialized, the program
increments and tests the STR Y retry counter. If a seek error persists after 10 tries, it is considered a
hard error. If 10 retries have not occurred, a branch is made to RETRY and the sequence repeated.

4.1.6.2 Empty Buffer Function - Figure 4-12 shows a program for implementing an empty buffer
function with interrupts turned off (lOF). The first instruction sets the number of retries at 10. A 2 is
set in the AC to indicate an Empty Buffer command and the command is loaded. When TR is set, the
program jumps to EMPTY to transfer a word to the BUFFER location. A jump is made back to loop
to wait for another TR. This process continues until either 64 words or 128 bytes have been emptied
from the sector buffer. When Done is set, the program tests to see if the error bit is set. If the error bit is
set, the program retries 10 times. If the error persists, a hard parity error is assumed, indicating a
problem in the interface cable.

4.1.6.3 Fill Buffer Function - Figure 4-13 presents a program to implement a fill buffer function. It is
very similar to the empty buffer example.
4-13

IPROGRAMMING EXAMPLES rOR THE RX8/RX0l FLEXIBLE OISKETTE
I

/THE rOllOWING ARE RX01 lOT CODE OErIN!110NS
I
/THE STANDARD lOT DEVICE CODE

IS 670-

I
67~1

6702
6703
6704
6705

6706
6707

IIOT TO LOAD THE CO~"ANC. (AC) IS THt COMMAND
IIOT TO LOAD OR READ THE TRANsrER REGISTER
IIOT TO SKIP UN • TRANsrER REQUEST FLAG
Ilor TO SKIP ON AN ERROR FLAG
IIOT TO SKIP ON THE DONE rL.G
I (AC) • 0 INTERRUPT ENAB!.E orF/ (AC) • 1 MEANS ON
IIOT TO INITIlLIAE T~E RXS/RX01 SUBSYSTEM

,-CO'6701
XOR'67~2

5TR'6703
SER:r67Z4
S,Jli::ll67~'

: 'IT.=6706

l'n"6707
I

/",;[ rOllO"INC IS • PROGRAM"ING EXAMPl.r or THE PROTOCOL

~EQUIREO

;

ITO "RI'£. HRlfE DELETED DATA, OR REAU AT 3EC TOR "5" (THE

I.DCHIC- SECTOR)

lIN 6 OR 12 BI' MODE

21
22

I
~2J0

23
2,

02Jl

02~2

125'
3255
1254

26
27
28
29
30

0ZZ3

3256

02~4

12"

02C5

33
3'
35
36
37

S'" ART,

TAO <1'110
DCA PTAy
TAO <HU
~CA

CTRy

ICRC RETRY COUN'ER
ISEEK RETRY COUNTeR

IrHU TE, wRPE DELErEO DA'l"A. OR READ

02"6
02J7

1260
1261

02~2

1262

~211

67~1

M~TRY •

U~ I T

I
~212

67~3

STR

0213

42
43

0214

JMP 1 .. 1
TA.O SECTOR

"216

5212
1263
6702
7200

/101 6'X3 TO
/WAI' rOR TRANsrER REQUEST ri.AG
I 1 TO 32(OCHLI
IIOT TO i.OAO SECTOR
lelA BECAUSE 10' XOR DOESN'T

xpR

CLA
/;.jA 1T
I

0217
0220
0221

6733
5217
1264

51
52

0222
0223

7200

ST.
JMP

II OT 67XJ TO
IWA I T rOA TRANSFER REQUEST
a TO 114(OCTAL)
nOT TO lOAD TRACK
ICCA BECAUSE lOT XCR DOESN'T

1-1

riO TRA;;K
XOR

67~2

Ci. A
11;;[ SECTOR AND 'RACK ADDRESSES HAVE

53
54
55
56

~[EN

TRANsrrRR"a TO THE

I~AIT

rOR THE DONE FLAG AND

CHEG~

VIA THE XOR lOT

rUR ANY ERRORS

IIF THE rUNCTION HAS COMPi.OED SUCCESSFULi.Y (NO ERROR ri..G' THEN HAL'
I

1101 67X' TO
IWAIT rOR OO~E FlAO
IIOT 67X4 SA"Pi.ES ERROR ri.A.

62
63
6'

nHE ERROR flAG

65
66
67

OK • COMPLtTED

IS SET

ITHE CONTENTS or THE TRA'ISFER

REGIST[~

15 THE ERROR STATUS

nr TRANSFER REGISTER BITS lB. AND 11 • 0 THEN SOHE TY~E or SEEK ERROR HAS aCCUREO.

68
69
70

11r TRANsrER REGISTER BIT 11 • 1 THEN
III' TRANSFER REGISTER BIT 10 ' 1 THEN

3233

73
74

02JZ

75
76

RX~l

57
58
59
60

•

T"E TRANSeE. REQ'JEST FLAG THE-, TRANsrER THE SECTOR ADDRESS

~21S

100 IF S-SIT
IF WRITE. l ' 17 wRITE OEi.ETED
lOA", O~ 6 Ir READ
I 3 I r UN IT 3, 20 Ir UNIT 1
IIOT 67Xl TO L.OAO THE CO"lMAND

~CO

45
46

n IF 12-eIT.

TAO "ODE
TAO COMMAND

/"4 A 1 T ro·

48
49

·U

IPARITy RETRy COUNTER

TAO KHU
DCA STPy

3257

31
32

or PROGRAM

CO~TENTS

or TRACK "T" (THE CONTENTS OF PROGRAM LOCATiO~ TRACK)

~Z31

0233
023'
0235

XOR

67C2
3265
7305
,,"'265
7650
5241

76
79
8?

CRC ERROR HAS OCCUREO.
PARITY ERROR HAS OCGUREO
IGET CONTENT,
lAND SAVE

DCA ASTATUS
CLio CL,' lAG RAi.
AND 'STATUS

or TR ( ERROR STATUS)

2
ITEST rOR PARITY ERROR
15K I' II' PARITY [RROR
I~Ol A PlRtTY ERROR - MAYBE eRe
I

SNA CLA

UH" TeRc

I, P,R!TY ERROR HAS aCCUREO
I

a1
a2

IANO RETRY THE" COM"ANO " UNTIL TH£

I
lOR J~ni.

;INCREMENT AND TEST THE

P'~ITY

ERROR METRY COUNTER pqOGRAM LOCATION
PA~ITV

PTqy "

ERROR RECOVERS

THE PTRY COUNTER OVERflOW' TO 0

3236

2255

86
89
ge

023'

5206
740<

0242

ISl PTRy
JMP RE'rFh

IRETRT THE COMMAND
I"ARO OAR I Tr ERROR

"L T
I

; iii£:

IrEST

94
95
96
97
95

02-1
0242
02<3
~244

7301

"'eRe,

c'265
7650
5250

Figure 4-11

CU CL A lAC
AND ASh TUS

1
IT[ST rOR A eRC ERROR
ISKIP II' A CRC ERROR
INOT A CRC • MUST SE A SEEK

SNA Clio

J"P SE[K

RX8E Write/Write Deleted Data/Read Example (Sheet 1 of 2)

4-14

14 CRC ERROR HAS OCCURED

100

121
122
103
124
105
126
127
138
139

/INCREMENT AND TEST THE CRC ERROR RETRY COUNTER

'ROGRA~

1.0CATION " CTRY •

IANO RETRy THE COMMAND UNTIl. THE CRC ERROR RECOVERS
I

lOR UNTIl. THE CTRY COUNTER OVERrLOWS TO 0
I

IS! CTRY
JM' RETRV
HI. T

124'
1246

8247

118
111

112

IREUY THE COMMAND
IHARD CRC ER~OR

/THE ERROR rl.AG IS SET

113

ITHE ERROR IS tNOTl A PARITY ERROR AND IS CNOTl A CRC ERROR

11'
115

,/THERErORE 15 MUST BE A SEEK ERROR

116

117

118
119
120
121
122
123

825.

6707

lAND RETRy THE COMMAND UNTIl. THE SEEK ERROR RECOVERS
I

lOR UNTIl. THE CTRY COUNTER OVERrLOWS TO 0
I

1$1 STAY
JHP RETRV
MI.T

8251
1252
8253

IREUV THE COMMAND,
IHARD SEEK E~ROR

/THE rOl.1.0W I HG PROCRAM LoOCAT IONS ARE HtHRENCEO WITH I N T~ IS EXAMPL.E
I

8254

777.

KHU.

-18

133
13'
135

136
137
138
139
140
141
142
1.3

IIOT 67X7 TO INITII\,IAE

INIT

IINCREHENT AND TEST THE SEEK ERROR RETRY COUNTER PROGRAM 1.0CATION " STNY •

130
131

132

SEEK.
I

l24
125

126
127
128
129

ICONTENTS or THE TRANsrER REGISTER HITS 11. AND 11 , II

1255
1256
8257

/THE rOI.L.OWING J PROcRAM I,OCATIONS ARE THE ERROR RETRY COUNTERS
I
IPARITY ERRO~ RETRy COUNTER
PTRY.
I
ICRC ERROR RETRV COUNTER
e
CTRy.
ISEEK [R~OR ~ETRV COUNTER
STRY.
e
I

IPROCRAM 1.0CA Tl ON • HODE • CONH 1NS A e I r 12-1 IT 'OOE. OR
ICO~TAINS A 1I~ Ir 8-BIT HODE

• OR UI

'lODE.

,1.44

145

IPROCRAM 1.0CATJOti " COMMAND" CONTAINS THE

146
147
148
149
150
151
152
153
15'

155

TO BE ISSUED VIA THE loCO lOT

IWRITE 141, WRITE DELETED DATA (14). OR READ (6). OR
I

0261

COMMA'ID. f

E~PTY

aUrrER (2)

4. 14. OR •• OR

IPROCRAM 1.0CATION " UNIT" CONTAINS
I

IUNIT

T~[

UNIT

O[$JG~ATION

(fl. OR UNIT 1 (2.,

1262

UNIT.

•• OR

156
157
158

159
160
161
162
163
164
165
166
167
168
169

COMHA~D

IPROGRAM 1.0CATlON " SECTOR· CONHINS THE SECTOR AOO_US 11 TO 32 OCTALoI
I

,s.crOR. I
IPROGRAM 1.0cnlON "

I
TRAC~

1 TO

a OCTAL

" CONTAINS THE TUCK ADDRESS II TO 114 OCTAI.I

1264

TRACK.
I

IPROCRAM 1.0CATION • ,STATUS· CONTAINS THE

•

CONTt~TS

IAT THE OETECTION or AN ERROR IERRQH rLAG • 1) WHICH

TO 114 OCTAl.
0' TWE UANsrER REGISTER
COR~ESPONDS

TO THE

'ERROR STATUS

17~

l71
172
173

• 3 I' SEEK [RROR. 1 I' CRe ERROR. 2 Ir ~ARITY ERROR

ISTATUS AT [UQR

'STATUS.

Figure 4-11

RX8E Write/Write Deleted Data/Read Example (Sheet 2 of 2)

4-15

228
229
2311
231
232
233
234
235
236
237
238
239
2411
241
242
243
244
245
246
247
248
249
2511
251
252
253
254
255
256
257
258
259
2611
261
262
263
264
265
266
267
268
269
2711
271
272

ITHE rO~~OWING IS A PROGRAMMING £XAHP~[ or PROTOCO~ REQUIRED TO
I

IEMPTY T~E SECTOR BurrER or 64 12-SIT WOROS (12 BIT HODEl, OR
I

IEMPTY THE SECTOR BurrER or 128 a-BIT BYTES (8 BIT MODE)
I

8H2

12'4
32"

IlJl4
831'
8316
111317
03211

1377
31118
1268
1261

[ENTRY, TAO KM11!
DCA PTRy
ESETUP, TAD (BUrrER-l)
DCA Ale
TAD MoDE
TAD COMMAND

8 TRYS TO [MPTy THE lECTOR 8urrER
IPARITY ERRO. RETRy COUNTER
IPROGRAMS DATA BurrER
IAUTO INDEX REGISTER 11
I I I' 12-BIT, 11111 Ir • alT
I 2 MEANI EH'TY Bu,rER
IIOT TO ISSUE THE COMMAND
I

~CO

67e1
I

IWAIT ro~ A TRANsrER REQUEST r~AG BErORE TRANsrERRING DATA TO THE ~ROGRAHS
I

10ATA BurrER rROM THE Rxal SECTOR BUrrEp.
I

IWAIT rOR A DONE r~AG TO INDICATE THE COHP~ETION or THE EMPTY BurrER COMMANO P~IOR TO

ITESTING THE ERROR 'LAG

8321

6703

11322

7410

111323

'333

11324

6795

1132'

5274

ITEST ro_ TR r~AG
ITA NOT lET, TEST 'OR DONE r~AG
ITA rL.AG SET
ITE5T rD~ DONE r~AO
INOT T~, OR OONE YET

[LOOP,

ITHE OONE 'LAG IS SET
I

ITEST rOR ANY [RRORS

(ON~Y

ERROR POSSIBLE IS A ~ARITY ERROR)

11326
11327

ITE&T 'OA THE ERROR r~AG
INO [RROIIS • OK

67114
7402
I

IINCREMENT AND TEST THE PARITY ERROR MfTRY PROGRA~ LOCATIoN· PTRY •

14NO RETRY THE COMMAND UNTI~ THE ERROM RECOVERS
I

lOR UNTI~ THE PTRY COUNTER OVERfLOWS TO 9
I

113311
111331
11332

2255
'314

I $I PTRY
JHP ESETuP

IRE TRY TO EM.TY THE SECTOR Bur'ER
IHARC PAftlTY ERROR

H~T

74~2

273

ITHE TRANS'ER REQUEST r~AG IS SET

274
275

276
277

278
279
2811

281
282

ITRANsrER OATA TO THE PROGRAMS DATA BurrER rROM THE Rxel SECTOR Bu,rER
I

111333
11334
1l33'

eJ77

67112
34U

EMPTY,

XDR
DCA I AU

'321

JM~ £~OOP

a4U

PAGE

0377

THC RXgl SECTOR BurFER
ITO THE 'ROG.AHS DATA IUFrER
ILOOP UNTIL THE DONE rLAG SETS
IrRO~

ITHE rO~~OWING PROGRAM ~OCAT!ONS ARE RESERVED roq THE PROGRA~S DATA BurrER
I

283

BUrrER, 9

284
285

eBurrER+2111

Figure 4-12

RX8E Empty Buffer Example

4-16

174
175
176
177
178
179
18B
181
182
183
18~

185
186
187
188
189
19B
191
192
193
194
195
196
197
198
199
2BII
201
232
2113

ITHE rO~~OWING IS A PROGRAMMING EXAHP~E or PROTOCO~ ~EQUIREO TO
I

IrlLL THE SECTOR BurrER WITH 64 12-SIT WORDS (12 BIT HODE), OR

IrlLL THE SECTOR BurrER WITH 128 a-SIT BYTES (8 SIT ~ODE)

011U

4111 0 19

12,4
32"
1377
301111
1261
671111

rENTRY, TAD KM18
DCA PTRy
SETUP, TAD IBurrER-l)
DCA Ale
TAO MODE
LCD

11266

8267

82711
111271
11272
11273

IWAiT rOR A TRANsrER REQUEST rLAG BEroRE TRANSrERRING DATA ,qOM THE PROGRAMS

10ATA BurrER TO THE Rxel SECTOR BurrEM
I

IWAIT rOR A DONE ,LAG TO 1.0ICATE THE COMPLETION 0' THE rILL BurrER COMMAND PRIOR TO

ITESTING T~E ERROR rLAC
I

1274
1il27'

111276
8277
830111

6783
671115

227

ITEST ro_ DO~E rLAG
I~OT T~, OR DONE YET

JM' ~OOP
ITHE DONE 'LAG IS SET

ITEST FOR ANY ERRORS (ONLY ERROR POSSIBLE IS A PARITy [RROR)

.,3111
8302

ITE5T roq THE ERROR rLAG
INO [RROIIS • OK

SEA
HLT

67e4

7402
/

IINCREHENT AND TEST THE PARITY ERROR HETRY PROGRAM LOCATIoN· prRY "
I

lAND RETRY THE COMMAND UNTIL THE ERROR RECOVERS

lOR UNTIL THE PTRY COUNTER OVERfLOWS TO e

215

219
2211
221
222
223
224
225
226

IU NOT lET,
/U 'LAG SET

211
212
213
214

218

ITtlT ro~ TR FLAG
TEST rOR DONE ,LAC:

ST~

SK'
JM' riLL
$D'I

5274

211'

216
217

coop,

7416

'306

211~

295
206
207
208
209

/ a TRYS TO 'ILL THE SECTOR BurrER
IPARITY ERROR RETRY COUNTER
IPROGRAM' DATA SUrrER
IAUTO INOEX REGISTER 11
I II I' 12-IIT, lee Ir a BIT
IIOT TO ISSUE THE COMMAND

113113
1304
83'"

22"
'27.

IS! PTRy
JH' SETUP

IRtTRY TO 'ILL" THE SECTOR BUFFER
IHARD ~ARITY ERROR

H~T

7402
I

ITHE TRANS'ER REQUEST 'LAG IS SET

ITRANSFEA OAT. ,ROM THE PRoeRAMS DATA BU,rER TO THE Axel SECTOR BU,rER

11306

141111

11307

"02

11318
11311

7211.
'274

riLL,

IVIA AUTO INDEX REGISTER Ie
ITO THE _Xll SECTOR Bu,rER
ICLA BECAUSE lOT XDR DOESN'T
ILOOP UNTIL THE DONE FLAG SETS

TAO I AU

XDA
CLA
JH' LOOP

Figure 4-13

RX8E Fill Buffer Example

4.1.7 RX28 Programming Examples
Figures 4-14,4-15, and 4-16 are programming examples for write, write deleted data or read functions,
for fill buffer functions, and for empty buffer functions, respectively. These examples are very similar
to the RX8E programming examples described in Paragraph 4.1.6. Basically, there are two differences
between the RX8E and RX28 examples. First, for the RX28 when a command is transferred in the 8bit mode of operation, it is transferred in two 8-bit words using an XDR to transfer the second
command word (see location 0225 in Figure 4-14); second, for the RX28, there is no parity error check
as there is in the RX8E; instead there is a density error check.

4-17

IP~O,"HI'G

flAMPLES ~O~ T.E R'28/! 'LEXI81.[ DISKETTE

""! rJL\.OwING ARE RX01 lOT COlE nE'INtTIo'S
I

H"O.OD lOT nVIC£ ODE IS b75.

IT"E
I

Leo.

lilT Tl I.DAO
lilT Tl 1.0iO
II)T TO S(I'
IIJT TO 5(1'

THE CO""ANO, (ACI IS THE CO".ANO
OR "ElO THE TUNS.ER REGISTER
ON T.ANSFER REQUEST 'LA.
ON to.OR FLA.
IIOT TJ 5(1" ~N 00"£ FLAG
J('CI.~ I"ER.U", ENAaLE OFF/CACI"1 "EANS ON
IIOT TO INITIALIZE THE RX 5u85'51["

xrl;jl.

5flfa

SEq.
SO~.
TNT~I:
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IT"! nLlD_IN_ IS • '.OG.'.I"G E''''LE OF THE .RDToeOL REQuIRED
I

ITJ .'ITE. WRrTE eE\.fTED Do", OR REAO AT SECTOR '5'

(THE tONTENTS O' .ROG.,"

It.-leAf lOr..!

"5fCTO~N)

0' TItAeJ( l'IT iI

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(THe: CONTENTS OF PIlOGtt''''

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OR 12 BIT

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l~"A.T'JS

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Figure 4·14

FOR CAe ERROR DIT

zno CRe

'Sh,TuS

/ I ' AC NUT

'E'5!T

II' At • " TIoIEIiol CHEt1( 'Ol:l

~E'T~'(

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OCCJRED SO

S~lp

oE~StTY

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Rn~H5

I' •

RET~lf5

TH!~

cl~

I-.AI..T

RX28 Write/Write Deleted Data/Read Example
(Sheet 2 of 2)

4·18

ERIHIOq

U T"E" SKIP
AGAI~I

IT.!

!~RO • • 'S

cqc S~ CMEC< 'OR WRO"

'JT •

DENSITY, IF CE'5!TY ERROR

I
I~JO

EXUT TojE, .. '~T, I' T"IS EO.J. OCCURS IT COULD JJST HAH

ISEE" !ECAUn wE .HGOf TO sn T"E O'GHT nfNSIT. 1_ T"E co .... n .D.~
I

InO IT COULD SE fME .RO.S

'IS'~'TE

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INSERTED I' fHE DRiVE OR

liT COWLO Af SOME JTHeO REas"

BUT Of

"'0. ,HAT CAUSED IT

SN"U~O

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I

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lAC •

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ITote !"MOIii MUS'

lAC. 20, 11151( FOR DEJ,iSlTY EI.,~OR
/I" STATUS .0"0 I' SET 5<1"
I I ' NOT oe'SIT' ER.OR "USf 8E SF-E. fUM
IHALT "'tTIoI O!NSITY ERROR ByT ~ET till At:

'STHUS

04&VE e.EEIt,j A 3F.!K EQIHH~

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I
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ill

1111 OCTA.L

TS uSE'

1'['1

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IF 1"4 EqilJQ JCClIqS.
q)~~E" IS SET.

I~EGI5TtQ

Tote:

TI-<l;.

tJ"IH.NT5

STAT1l5 15 11>,1 Tl"lf.

T-IE

5'1'.&1.)5

TQA~jSFF'"

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ASfALJS,

Figure 4-14

RX28 Write/Write Deleted Data/Read Example
(Sheet 2 of 2)

4-19

art

""E '~LLowl~; IS •

~RDG.A'"I~.

"ILL IHE IECID' 8J,nR
Ule

AlhlP
I

n'''Y, UO

SETU',

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DCl
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IGET COMMAND " AC
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IGH SAYEO CO. "AND -0.0
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'caM.ANO WOAD 00 •• TO THE
I. L5S'S (RITS 8",I~,ltl O' Ae
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I I ' r. NOT SET Lno. U"TIL IT nOES
"SSUE SECOND to."AN~ -nRD
IClEAR TH! Ae IN' no 'ILL LOOP

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I

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I

100 J.rIL THE ETO, tOU_TE" ry'FO'L~'S TO
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I

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I

FJi..L,

TAD I ' I '
10'

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ITO THE Axel SEtTO' ijd'ff.
ItlA REClUSE IJT I~' ~OfS_'T
'LJO' U~TIL T"E QO.E 'LAG 5ETS

c.>

J"' LJD'
Figure 4-15

RX28 Fill Buffer Example

4-20

•• ,n. TO

IT~f

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IfoPTY

nl5

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IP.OGR1M, DATA BU',ER
IA~TD INDEX REGISTER II
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~u'H.

~UI

lOt

J.'

'LOO' UNTIL T.! nONE 'L.; IE IS

1341
U'2
.6U

"if
""£ ,JLLowlk'
"oG'"

Ja'1
IlU

Bu'F fit, "

LOt.'IOYS .O! R£5£ •• £0 FO' THE "OGo,_s OAT' BuFFER

aU0

<euFFER·'sa

•

Figure 4-16

RX28 Empty Buffer Example

4-21

4.1.8

Restrictions and Programming Pitfalls

A set of 11 restrictions and programming pitfalls for the RX8E is presented below.

When performing the following sequence of instructions, interrupts must be off.
STR
SKP
JMP
SON
JMP
(done)
(fill or empty buffer)

If interrupts are not off, the following sequence of events will occur. Assume interrupts are
enabled and the RX8E issues an interrupt request just before the SON instruction; the SDN
instruction will be executed as the last legal instruction before the processor takes over.
However, since the done flag is cleared by the SON instruction, the processor will not find
the device that issued the interrupt.
2.

The program must issue an SER instruction to test for errors following an SON instruction.

For maximum data throughput for consecutive writes or reads in 8-bit mode, interleave
every three sectors; in 12-bit mode, interleave every two sectors. (This of course depends on
program overhead.)

When issuing the lOT XOR at the end of a function to test the status, the instruction AND
377 must be given because the most significant bits (0-3) contain part of the previous command word.

If an error occurs and the program executes a read error register function (Ill) (Paragraph
4.1.4.9), a parity error may occur for that command. The error code coming back would not
be for the original error in which the read error register function was issued, but for the
parity error resulting from the read error register function. Therefore, check for parity error
with the read status function (101) before checking for errors with the read error register
function (lIl).

The SEL OR V ROY bit is present only at the time of the read status function (10 1) for
either drive, or at completion of an Initialize for drive O.

It is not necessary to load the drive select bit into the command word when the command is
Fill Buffer (000) or Empty Buffer (001).

Sector Addressing: 1-26 or 1-328 (No sector 0)
Track Addressing: 0-76 or 1-1148

If a read error register function (Ill) is desired, the program must perform this function
before a read status function (101), because the content of the error register is always modified by a read status function.
4-22

lO.

The instructions STR, SDN, SER also clear the respective flags after testing so that the
software must store these flags if future reference to them is needed after performing one of
these instructions.

II.

Excessive use of the read status function (101) will result in drastically decreased throughput
because a read status function requires between one and two diskette revolutions or about
250 ms to complete.

4.2 RXl1 AND RXVU PROGRAMMING INFORMATION
This section describes device registers, register and vector address assignments, programming specifications, and programming examples for the RXII and RXVII interfaces.
All software control ofthe RXIl/RXVll is performed by means of two device registers: the command
and status (RXCS) register and a multipurpose data buffer (RXDB) register. These registers have been
assigned bus addresses (Paragraph 4.2.1) and can be read or loaded, with certain exceptions, using any
instruction referring to their addresses.
The RX02, which iricludes the mechanical drive(s), read/write electronics, and ,uCPU controller, contains all the control circuitry required for implied seeks, automatic head position verification, and
calculation and verification of the CRC; it has a buffer large enough to hold one full sector of diskette
data (128 8-bit bytes). Information is serially passed between the interface and the RX02.

A typical diskette write sequence, which is initiated by a user program, would occur in two steps:
1.

Fill Buffer - A command to fill the buffer is moved into the RXCS. The Go bit (Paragraph
4.2.2.1) must be set. The program tests for transfer request (TR). When TR is detected, the
program moves the first of 128 bytes of data to the RXDB. TR goes false while the byte is
moved into the RX02. The program retests TR and moves another byte of data when TR is
true. When the RX02 sector buffer is full, the Done bit will set, and an interrupt will occur if
the program has enabled interrupts.

Write Sector - A command to write the contents of the buffer onto the disk is issued to the
RXCS. Again the Go bit must be set. The program tests TR, and when TR is true, the
program moves the desired sector address to the RXDB. TR goes false while the RX02
handles the sector address. The program again waits for TR and moves the desired track
address to the RXDB, and again TR is negated. The RX02 locates the desired track and
sector, verifies its location, and writes the contents of the sector buffer onto the diskette.
When this is done, an interrupt will occur if the program has enabled interrupts.

A typical diskette read occurs in just the reverse way: first locating and reading a sector into the buffer
(read sector) and then unloading the buffer into core (empty buffer). In either case, the content of the
buffer is not valid if Power Failor Initialize follows a fill buffer or read sector function.

4.2.1 Register and Vector Addresses
The RXCS register is normally assigned Unibus address 177170 and the RXD B register is assigned
Unibus address 177172. The normal BR priority level is 5, but it can be changed by insertion of a
different priority plug located on the interface module. The vector address is 264.
4-23

4.2.2

RXCS - Command and Status (177170) - Loading this register while the RX02 is not busy and
with bit 0= 1 will initiate a function as described below and indicated in Figure 4-17. Bits 0-4 are writeonly bits.

4.2.2.1

INT
ENB

RX
INIT

Figure 4-17

UNIT
SEL

RXCS Format(RXII, RXVII)

Bit No.

Description

Go - Initiates a command to RX02. This is a write-only bit.

1-3

Function Select - These bits code one of the eight possible functions listed below and described in Paragraph 4.2.3. These are write-only bits.
Code
000
001
010
011
100
101
110
111

Function
Fill Buffer
Empty Buffer
Write Sector
Read Sector
Not used
Read Status
Write Deleted Data Sector
Read Error Register

Unit select - This bit selects one of the two possible disks for execution of the desired
function. This is a write-only bit.

Done - This bit indicates the completion of a function. Done will generate an interrupt when
asserted if Interrupt Enable (RX2CS bit 6) is set. This is a read-only bit.

Interrupt Enable - This bit is set by the program to enable an interrupt when the RX02 has
completed an operation (Done). The condition of this bit is normally determined at the time
a function is initiated. This bit is cleared by Initialize and is a read/write bit.

Transfer Request - This bit signifies that the RXII or RXV11 needs data or has data available. This is a read-only bit.

8-13

Unused

RX Initialize - This bit is set by the program to initialize the RXll or RXV11 without
initializing all devices on the Unibus. This is a write-only bit.
CAUTION
Loading the lower byte of the RX CS will also load
the upper byte of the RX CS.
4-24

Upon setting this bit in the RXCS, the RX 11 or RXVll will negate Done and move the
head position mechanism of drive 1 (if two are available) to track O. Upon completion of a
successful Initialize, the RX02 will zero the error and status register, set Initialize Done, and
set RXES bit 7 (DRV ROY) ifunit 0 is ready. It will also read sector 1 of track 1 on drive O.
15

Error - This bit is set by the RX02 to indicate that an error has occurred during an attempt
to execute a command. This read-only bit is cleared by the initiation of a new command or
an Initialize (Paragraph 4.2.6).

4.2.2.2 RXOB - Data Buffer Register (177172) - This register serves as a general purpose data path
between the RX02 and the interface. It may represent one of four RX02 registers according to the
protocol of the function in progress (Paragraph 4.2.3).
This register is read/write if the RX02 is not in the process of executing a command; that is, it may be
manipulated without affecting the RX02 subsystem. If the RX02 is actively executing a command, this
register will only accept data if RXCS bit 7 (TR) is set. In addition, valid data can only be read when
TR is set.
CAUTION
Violation of protocol in manipulation of this register
may cause permanent data loss.
4.2.2.3 RXTA - RX Track Address (Figure 4-18) - This register is loaded to indicate on which of the
77 (1148) tracks a given function is to operate. It can be addressed only under the protocol of the
function in progress (Paragraph 4.2.3). Bits 8-15 are unused and are ignored by the control.
15

I I

,
0-114,

NOT USEO

Figure 4-18

RXTA Format (RXlljRXVll)

4.2.2.4 RXSA - RX Sector Address (Figure 4-19) - This register is loaded to indicate on which of the
26 (32 8) sectors a given function is to operate. It can be addressed only under the protocol of the
function in progress (Paragraph 4.2.3). Bits 8-15 are unused and are ignored by the control.
15

I I I I I I I I I I

I I I

NOT USEO
CP 1511

Figure 4-19

RXSA Format (RXlljRXVll)

4.2.2.5 RXOB - RX Data Buffer (Figure 4-20) - All information transferred to and from the floppy
media passes through this register and is addressable only under the protocol of the function in progress (Paragraph 4.2.3).
15

I I II I I I I I I II

I III
MA-1866

Figure 4-20

RXDB Format (RXI IjRXVI I)

4-25

4.2.2.6 RXES - RX Error and Status (Figure 4-21) - This register contains the current error and
status conditions of the drive selected by bit 4 (U nit Select) of the RXCS. This read-only register can be
addressed only under the protocol of the function in progress (Paragraph 4.2.3). The RXES content is
located in the RXD B upon completion of a function.

'----~'Y

NOT USED

Figure 4·21

UNIT

III II I

SEL DRV

DRV

RDY

DEN

CRC

RXES Format (RXII, RXVII)

RXES bit assignments are:
Bit No.

Description

CRC Error - A cyclic redundancy check error was detected as information was retrieved
from a data field of the diskette. The RXES is moved to the RXDB, and Error and Done are
asserted.

Initialize Done - This bit is asserted in the RXES to indicate completion of the Initialize
routine which can be caused by RX02 power failure, system power failure, or programmable
or Unibus Initialize.

Density Error - This bit is asserted to indicate the density of the function in progress does
not match the drive density. Upon detection of this error the control terminates the operation and Error and Done are asserted.
NOTE
Bits 4 and S are asserted for the occurrence of double
density when the system is RXOl-compatible.

Drive Density - This bit indicates the density of the diskette in the drive selected. When
asserted, double density is indicated.

Deleted Data Detected - During data recovery. the identification mark preceding the data
field was decoded as a deleted data mark (Paragraph 1.5.3.2).
4·26

Drive Ready - This bit is asserted if the unit currently selected exists, is properly supplied
with power, has a diskette installed correctly, has its door closed, and has a diskette up to
speed.
NOTE 1
The drive ready bit is only valid when retrieved via a
read status function or at completion of Initialize
when it indicates status of drive O.
NOTE 2

If the error bit was set in the RXCS but error bits are
not set in the RXES, specific error conditions can be
accessed via a read error register function (Paragraph 4.2.3.7).
8

Unit Select - Drive 0 is selected if this bit is "0"; drive 1 is selected if this bit is a "I."

4.2.3 Function Codes
Following the strict protocol of the individual function, data storage and recovery on the RX 11 and
RXVII occur with careful manipulation of the RXCS and RXDB registers. The penalty for violation
of protocol can be permanent data loss.
A summary of the function codes is presented below:
000

001
010
011
100
101
110
III

Fill Buffer
Empty Buffer
Write Sector
Read Sector
Not used
Read Status
Write Deleted Data Sector
Read Error Register

The following paragraphs describe in detail the programming protocol associated with each function
encoded and written into RXCS bits 1-3 if Done is set.
4.2.3.1 Fill Buffer (000) - This function is used to fill the RX02 buffer with 128 8-bit bytes of data
from the host processor. Fill buffer is a complete function in itself; the function ends when the buffer
has been filled. The contents of the buffer can be written onto the diskette by means of a subsequent
write sector function, or the contents can be returned to the host processor by an empty buffer function.
RXCS bit 4 (Unit Select) does not affect this function since no diskette drive is involved. When the
command has been loaded, RXES, OUT, and Done are cleared. When the TR bit is asserted, the first
byte of the data may be loaded into the data buffer. The control then clears TR and after supplying the
appropriate number of shift pulses to store the data, again asserts TR. The same TR cycle will occur as
each byte of data is loaded. The RX02 counts the bytes transferred; it will not accept less than 128
bytes and will ignore those in excess. Any read of the RXDB during the cycle of 128 transfers is
ignored by the RX II jRXVll. When the complete buffer has been filled, the control asserts Done.
4.2.3.2 Empty Buffer (001) - This function is used to empty into the interface the buffer of the 128
data bytes loaded from a previous Read Sector or Fill Buffer command. This function will ignore
RXCS bit 4 (Unit Select) and negate Done. For this function, TR and shift pulses are generated in the
same manner as for the fill buffer but the buffer is emptied.

4-27

When TR sets, the program may unload the first of 128 data bytes from the RXDB. Then the
RX IljRXVll again negates TR. When TR resets, the second byte of data may be unloaded from the
RXDB, which again negates TR. Alternate checks on TR and data transfers from the RXDB continue
until 128 bytes of data have been moved from the RXDB. Done sets, ending the operation.
NOTE
The empty buffer function does not destroy the contents of the sector buffer.

4.2.3.3 Write Sector (010) - This function is used to locate a desired track and sector and write the
sector with the contents of the internal sector buffer. The initiation of this function clears TR and
Done.
When TR is asserted, the program must move the desired sector address into the RXDB, which will
negate TR. When TR is again asserted, the program must load the desired track address into the
RXDB, which will negate TR. If the desired track is not found, the RXII jRXVl1 will abort the
operation, move the contents of the RXES to the RXDB, set RXCS bit 15 (Error), assert Done, and
initiate an interrupt if RXCS bit 6 (Interrupt Enable) is set.
TR will remain negated while the RX02 attempts to locate the desired sector. If the RX02 is unable to
locate the desired sector within two diskette revolutions, the RXII jRXVll will abort the operation,
move the contents of the RXES to the RXDB, set RXCS bit 15 (Error), assert Done, and initiate an
interrupt if RXCS bit 6 (Interrupt Enable) is set.

If the desired sector is successfully located, the RXl1jRXVll will write the 128 bytes stored in the
internal buffer followed by a 16-bit CRC character that is automatically calculated by the RX02. The
RXII jRXVII ends the function by asserting Done and initiating an interrupt if RXCS bit 6 (Interrupt
Enable) is set.
NOTE 1
The contents of the sector buffer are not valid data
after a power loss has been detected by the RX02.
The write sector function, however, will be accepted
as a valid function, and the random contents of the
buffer will be written, followed by a valid eRe.
NOTE 2
The write sector function does not destroy the contents of the sector buffer.

4.2.3.4 Read Sector (011) - This function is used to locate a desired track and sector and transfer the
contents of the data field to the jLCPU controller sector buffer. The initiation of this function clears
RXES, Done, and OUT.
When TR is asserted, the program must load the desired sector address into the RXDB, which will
negate TR. When TR is again asserted, the program must load the desired track address into the
RXD B, which will negate TR.

If the desired track is not found, the RX II jRXVll will abort the operation, move the contents of the
RXES to the RXDB, set RXCS bit 15 (Error), assert Done, and initiate an interrupt if RXCS bit 6
(Interrupt Enable) is set.
4-28

TR and Done will remain negated while the RX02 attempts to locate the desired track and sector. If
the RX02 is unable to locate the desired sector within two diskette revolutions after locating the
presumably correct track, the RX II jRXVll will abort the operation, move the contents of the RXES
to the RXDB, set RXCS bit 15 (Error), assert Done, and initiate an interrupt if RXCS bit 6 (Interrupt
Enable) is set.
If the desired sector is successfully located, the control will attempt to locate a standard data address
mark or a deleted data address mark. If either mark is properly located, the control will read data from
the sector into the sector buffer.

[f the deleted data address mark was detected, the control will assert RXES bit 6 (DD). As data enters
the sector buffer, a CRC is computed, based on the data field and CRC bytes previously recorded. A
non-zero residue indicates that a read error has occurred. The control sets RXES bit 0 (CRC Error)
and RXCS bit 15 (Error). The RXlljRXVll ends the operation by moving the contents of the RXES
to the RXD B, sets Done, and initiates an interrupt if RXCS bit 6 (Interrupt Enable) is set.
4.2.3.5 Read Status (101) - The RX II jRXVll will negate RXCS bit 5 (Done) and begin to assemble
the current contents of the RXES into the RXDB. RXES bit 7 (Drive Ready) will reflect the status of
the drive selected by RXCS bit 4 (Unit Select) at the time the read status function was given. All other
RXES bits will reflect the conditions created by the last command. RXES may be sampled when
RXCS bit 5 (Done) is again asserted. An interrupt will occur if RXCS bit 6 (Interrupt Enable) is set.
RXES bits are defined in Paragraph 4.2.2.6.
NOTE
The average time for this function is 250 ms. Excessive lise of this function wm result in substantially
reduced throughput.
Deleted Data (nO) - This operation is identical to function 010 (write
4.2.3.6 Write Sector
sector) with the exception that a deleted data address mark precedes the data field instead of a standard data address mark (Paragraph 1.5.3.2).
4.2.3.7 Read Error Code Function (111) - The read error code function can be used to retrieve explicit
error information provided by the ,uCPU controller upon detection of the general error bit. The function is initiated, and bits 0-6 of the RXES are cleared. Out is asserted and Done is negated. The
controller then generates the appropriate number of shift pulses to transfer the specific error code to
the interface register and completes the function by asserting Done. The interface register can now be
read and the error code interrogated to determine the type of failure that occurred (Paragraph 4.2.6).
NOTE
Care should be exercised in the use of this function,
since under certain conditions, erroneous error information may result (Paragraph 4.2.5).
4.2.3.8 Power Fail - There is no actual function code associated with Power Fail. When the RX02
senses a loss of power, it will unload the head and abort all controller action. All status signals are
invalid while power is low.
When the RX02 senses the return of power, it will remove Done and begin a sequence to:
I.
2.
3.
4.
5.

Move drive 1 head position mechanism to track O.
Clear any active error bits.
Read sector 1 of track 1 of drive 0 into the sector buffer.
Set RXES bit 2 (Initialize Done) (Paragraph 4.2.2.6) after which Done is again asserted.
Set Drive Ready of the RXES according to the status of drive O.
4-29

There is no guarantee that information being written at the time of a power failure will be retrievable.
However, all other information on the diskette will remain unaltered.
A method of aborting a function is through the use of RXCS bit 14 (RX Initialize). Another method is
through the use of the system Initialize signal that is generated by the PDP-II RESET instruction, the
console START key, or system power failure.
4.2.4

Programming Examples

4.2.4.1 Read Data/Write Data - Figure 4-22 presents a program for implementing a write, write
deleted data, or a read function, depending on the function code that is used. The first instructions set
up the error retry counters, PTR Y, CTR Y, and STR Y. The instruction RETRY moves the command
word for a write, write deleted data, or read into the RXCS.
The set of three instructions beginning at the label 1$ moves the sector address to the RXll/RXVll
after transfer request (TR), which is bit 7, has been set. The three instructions beginning at the label 2$
move the track address to the RXll/RXVll after TR has been set. The group of instructions beginning at the label 3$ looks for the done flag to set and checks for errors.
An error condition, indicated by bit 15 setting, is checked beginning at ERFLAG. If bit 0 is set, a CRC
error has occurred, and a branch is made to CRCER. If a parity error has occurred, a branch is made
to PARER. If neither of the above occurs, a seek error is assumed to have occurred and a branch is
made to SEEKER, where the system is initialized. In the case of a write function, the sector buffer is
refilled by a JMP to FILLBUF. In the case of a read function, a JMP is made to EMPBUFF.
In each of the PAR, CRC, and SEEK routines, the command sequence is retried 10 times by decrementing the respective retry counter. If an error persists after 10 tries, it is a hard error. The retry
counters can be set up to retry as many times as desired.
NOTE
A fill buffer function is performed before a write
function, and an empty buffer function is performed
after a read function.
4.2.4.2 Empty Buffer Function - Figure 4-23 shows a program for implementing an empty buffer
function. The first instruction sets the number of error retries to 10. The address of the memory buffer
is placed in register RO, and the Empty Buffer command is placed in the RXCS. Existence of a parity
error is checked starting at instruction 3$. If a parity error is detected, the Empty Buffer command is
loaded again. If an error persists for 10 retries, the error is considered hard.
If no error is indicated, the program looks for the transfer request (TR) flag to set. The error flag is
retested if TR is not set. Once TR sets, a byte is moved from the RXII /RXVII sector buffer to the
core locations of BUFFER. The process continues until the sector buffer is empty and the Done bit is
set.
4.2.4.3 Fill Buffer Function - Figure 4-24 presents a program to implement a fill buffer function. It is
very similar to the empty buffer example.
4.2.5 Restrictions and Programming Pitfalls
A set of restrictions and programming pitfalls for the RXll/RXVll is presented below.
I.

Depending on how much data handling is done by the program between sectors, the minimum interleave of two sectors may be used, but to be safe a three-sector interleave is recommended.
4-30

.AlS

,
,

,PRO'RAMMI~G EXAMPLES

'OR THE RXll/RWil 'LLXlIlE ~ISKETTE

,TH[ rOLLOWING IS THE AX1l STANDARD OEVICE ADDRESS AND VECTOR AOORUS

177170
177112
177172

8
9

117172

11
12
13
1,

15
16
17
18

eue',

eeiiS.
00BIl4

RXCS·PH"

COMMAND STATUS REGISTER

RXOhl71172
RXSAll77172

SEC'OR ADDRESS RIIHITER

RXTA'177172
RXESol11172

T.ACK AOORUS .UIITrR
E.ROR ITA 'US R[O I STER

,
e12 767
H27&?
012767

171770
111773
177773

000329
010114
BUllS

19
20
21

S'!'A~TI

BIT • • 1 "EANS UNIT 1 ( • II MUHlI UNIT "

,, ep! J TWRU
RETRY: "OV CO""AND, .xes
,

1 II I~t COM. AND I • • WRITt,

001022

oeeel'

1.,767
001715

•• ee36

116767

~0Be3e

eEQ 11
171126
I

lB
)9

08eS<4
S80050

.03852

1o,767
08117,
116767

17712J

28:

ISTB RXCS
BEQ ZS

Mova HUCK,

41
'2
43

~xrA

ITHE SECTOR 'NO TR.eK 'OORESSES "AVE BEEN TRANS'ERREO TO THE .XIl1

,;WS.I T 'OR 'WE DONE '1.'. 'NO CHECK '0" ,., ERRORS

"45

' I ' THE 'UNCTlo" HAS CO".I.£T£O SJCC[SSru", INa [RROR 'LAG)

" <anas
48

~J2767

0001166

,2101714

eBU'8

00!P67

0~"e74

0eHh~1

52
5,
55
5.
57
58
59
60
01

0eU76

Z~~00e

S80100
088106

MOV8 SECTOR • • XS'

,,WA I I 'OR THE TRANS't" REgUtST rl..G TWEN ro"SrER TWE rUCK AOORtn

Tsn Axes

15:

l' , W~ITt OEI-ETtD DATA, 6 • RUD,

; UNIT. IWRITE, WRITt ounco DHA, OR R[ADI

,;W'IT rO" THE TR.Nsr," R[gUEST rl.AG THEN UANsrE" THt 'ECTOR ADORUS

30
31
l'
35
36

MOV '-11. STRV

9115 • THRU 1 O' PROOHAM 1.0CATION CO""ANO OONTAIN THE 'UNCTiON

32
33

; ml~h:~T:~u~~~=TtR
, SEEK RnR' COUNTU

!"lOV '-11, pTRY
MQV '-lS, eTAY

;WRITE. WRITE DELETED DATA, OR RUO

22
23
2'
26
27
26

DATA lu.rER REG liTER

BED 35
1ST Axes
SNE ERrLA.

117074

1H[N HALT

m' J~~~\' T~~[ Dg~~(~~~G SETS

91' 'OON[OP, AXCS

TtST rOR THE [RROR 'LAG
BNE I r AN [RROR HAS aCcuRtO
O~ • COM'\,flEO

i1AI.. T

iTIolE ERROR rLAG IS srT
I n.1£

CON'I'(~fS

oF'

T\.4(

~u:(S

T~E

EftllOR STATUB

'I'
THE AXES 91 IS 1 AND a .
THEN SOME TYPE 0' 5tt< ['.OR OCCUR to
'Ir 'HE .XES 51 T e • 1 THEN' CRC [RROR HAS aCcuRtO
; I; THE AXES BIT 1 • 1 'MEN' .upv ERROR "AS OCCUR EO
;

8J8110
iH!!IiiH16

an '3, RXES

001'14
232767

aEe SEE"

TOT rOR cRe AND ••• pv E.RO'$
NOT' ' •• ITY OR CRe tMUS') BE • SEEK

Bl'!" 1112, lUES

TEST rOR PARITV fRROR

001'0'

BED CRe

NOT' ""ITY E•• OR lMusn It , eRe

~J.2 76 7

(RF'\.. .. CI

66
67

;

; I'ICREMt~T .NO TEST THE

70
71

76
77

E".o. RORV COUNTER 'RoORAM LOCATiON' ,TRY •

lOR UNTIl. THE pTRV COV"ER OVER'_Ow5 TO

73
74

"~Py

;AND Rnov THE· CO""ANO " UNTIL TME PARITV E.'OR "(COHRS

08i120
.8112'
000126

00'267

•• ,336

! Ne PTRV
SNE RETRy

080808

Io!A\". T

RElAY !HE COMMANO
"UO PARITY tRROR

; ACRe ER.O" "AS atCUNEO

,INeRt"E'1T '"0 'EST THE CRC E•• O. RETRY COUNTER .ROGRAM ,0CHloN " CTRY "

81
82
63

;

,,.NO

8'
6.
87

88
89

R(TRY

THE COMMAND UNTIl. THE CRC tR'OR RECoVERI

lOR V"l'l"U. 'l'HE: CT~Y COUNTE:R OVOI'I,.OWS To
;

65
000130
00813"
000136

005267
JHl32

CRe I

J000J0

91
92

t ~c CTRY
aNE RETRy

RETRY THE CO"M,NO

WAL T

>IMP eRC ERROR

,"HE ERROR 'LAC IS SET
;

95
96

;THERE' ORE IT MUST BE A SHK ERROR

;THE ERROR IS [NOTl A .ARITY ERROR ''0 II [NOT) , eRe [RRO'

••

, (STATE or AxeS BIlS

'NO 1 U[ I)

96
99

SEEK :

100

101

) INCREHENT AND TEST TN[ SEEK ER~O~ ~[TRY eoU~TER PROGRA. "OCATION • SUV •

102
103

lAND RETOV THE COM"AND UNril. TWE SEE~ ERAOR RECovERS

104
105
10.

107

108
109

lOR UNTIl. THE CTRY COUNTER oVERr"OW$ TO
I

001146
eU152
eU15'

005267
0B1323
000000

Figure 4-22

INC STRY
8N( RETRV

~[!.Y

104J.1..'!'

HUO stEK fRROR

THE eO"HAND

RX II /RXVII Write/Write Deleted Data/Read Example

4-31

16e
161
162
163
164
165
166
167
168
169
179
171
172
173
174
115
176
177
178
179

ITHE rO~LOWING IS A PROGRAHMING [XAM'LE or P~OTOeOL REQUIRED TO

I EMpTY

UI254

312767
a12799

1711711
O!lU42

~16767

~00.'4

IWAIT FOR A DoNE r~AC TO
IP~loR

ln767
0eU14

ELOOPI

176722

~~pn

HMI

001171
I

ITHE DoNE rLAG IS SET

,TEST FOR ANY [RRORS (oNLY ERROR poSSIBLE IS A PARITY [RRORI

~U3011

~0'767

IlU314

0018111

\lU306

00UU

TST RXCS

176664

BNt 15

HALT

IINCFEHE~T

AND TEST THt PARITY ERROR R[T~Y P_OCRAM LOCATioN' pTRY •

lAND RETRY THE COMMANU UNTIL THE ERROR RECoVERS

lOR UNTIL THE PTRY CUNTER oVERrLoWS To I

~003lS

JUJl4
J~9316

J0'267
391355
il0U00

~98

I
I

INC PTRY
BNt ESETuP
HALT

RETRY TO E~PTY THE SECTOR BurrER
PARITV ERROR

~ARD

ITHE TRANSrER REQUEST 'LAG Is SET

ITRAN5rER DATA TO THe PHDGRAH

2~1

176646

000320
000324

EMPTYI

DATA BUrrER FROM THE RXll SECTOR BUrFeR

~2V~~~~~B. '(Hal-

ITHE rOLLOW!NG J PROCH AM LOCATIO~S ARE

elle326
310330
aU332

3~1Il00
~JU0e

"~U09

T~E

[_ROR RETRY COUNTERS

I 'ARITY ERROR RETRY COUNTER
; CRe ER~OR _tTRy COUNTEI SEEK [qROR RETRY COU~TER

PTRy:
CTRy:
STRV:
I

IPROGRAM ~OCATIDN " COMMAND • CO~TAI~S T~E COMHAND To BE ISSUED VIA THE LCO loT

2~2

IWRITE (41. HRIH DELeTED DATA (141. oQ ~EAO (61. OR EH~TV BUFrER (21

088334

03uae

COHMA~DI

; •• 14, 6. OR 2 • (GO BIT 1 • 11

IPROCRAM LOCATION • S~CTOR • CONTAINS THC SECTOR AOOREIS (1 TO 32 OCTA~I

091336

ouelll

SECTOR I 2

; 1

TO H OCTAL

221

'PROGRAM ~OCATloN " THACK • CONTAINS T~E TRACK AODAESS (e TO 114 OCTAL)

222

0011340

00111000

225
226
227
228
229
231
231
232

TEST rOR T.ANSFER REQUEST 'LAG
INE Ir TRA~srER REQUrST 'LAG IS SET
TEST rOR DONE rLAG
IEQ UNTIL THE DONE FLAG ItTS

T5TB RXCS
81 T 'OONES IT. AXCS
BEQ ELOOP

176672

~32767

199
200

223
224

THE Co~pLETloN 0' THE EMPTY BUrrER COMMAND

TO TESTIN G THE ERROR r~AG

081262
1188266
00827111
US276

15:

220

I~DICATE

;

213
214
2.5
216
217
218
219

PROHGRAMS DATA BUFrt~
ISSUE THE eOMHANO

;DATA BurFER rRoN THE RXSl SECTOR Bur'ER

192

2.,,6
207
208
2e9
211
211

8 TRYS TO [MPTY THE lECTOR Bur FER

;WAIT FOR A TRANSFER REgUEST FLAG 8£'0_£ TRA~S'ERRING OATA TO THE PROGRAMS

193
194
195
196
197

202
203
204

'-u.

[ENTRY I MOV
pTRY
[SETUP I HOV nurFER. H0
COMHA~D.
Rxes
HOV
I

lSS
181
182
183
18 4
185
186
187
188
189
199
191

SECTOR HUrrER or 12. a·81T BYTES

TilE

U1242
81125111

TRACK I

; a TO 114 OCTAL

IPROCRAM EQUIVALE~TS

oaU41l
34\1800

aU342
308542
a00801

OONEBITo4B
INIT.4UU
BUFrER- •
.>auFFER-zea
.ENO

Figure 4-23

RXII/RXVII Empty Buffer Example

4-32

,,THE

111
112
113
114
115

,
,
e.1156
SSI164
eel17'

~1276'

0127ee
016767

17777a
00e342
D3014e

I TAYS TO 'ILL THE SECTOR Bu,rER
'ROGRl"S OATA BurrER
ISSUE THE COH"AND

rENTRY; HOV '-11, PTRY
SETUP' MOV 'BUFrER, RI
MOV CO"HAND, HXCS
I

;WlIT rOR A TRANSFER H[QUEST 'LAG 8E'ORE TRANSFERRING DATl 'ROM THE PROGRA~S
I

,DATA sUrrER TO THE RXll SECTOR !Urr[R

'WAIT rON A DONE rLAT TO

I~OICAT[

TH[ COMPLETIoN

or THE 'I,L SUrrER COMMAND

;PRloR Yo TESTING THE ERROR rLAG

,
ell176
08'2S2
sel214
SSI212

le,767
001414
032767
101771

176766

,OOP'

e~ee40

TtST rOR T.ANSrER REaUEST 'LAG
IEQ Ir T~ANsrEA REQUEST rLAG SET
TEST 'OR TWE DONt 'LAG
Ita UNTIL THE DONE r~AG SETS

TSTB RXCS
n~1

n~L

BIT 'DONEBIT,
BEO LOOP

Rxes

,ITHE DONE rLAG IS SET

'TEST rcR ANY ERReRS CONLY ERROR POSSIBLE IS A PARITY ERRORI

00e214
se822.
01'222

0S,767

TST RXCS

176750

001801
eeeosl

aNE 15

HA,T

;INCREM[NT AND TEST THE PARITY ERROR RETRY PftOGRAM ,OClTIOH • PTAY "
I

'AND RETRY THE

CO~MANO

UNTIL THE ERROR RtCQVERS

lOR UNTI~ THE pTRY COUNTER

148

149
15S
151
152
153
154
155
156
157
158

IS A PAOGRA""ING EXlH'LE or TWE PROTOCOL REQUIRED TO

, NOTE; THE DlTA TO riLL THE SECTOR BU,rER CAN BE ASSEMBLED IN COAE IN THE
I
EVEN ADDRESSES BYTES or lze WORO' OR IN BOTH BYT[S or 64 WORDS

116
117

118
119
120
121
122
123
124
125
126
127
128
129
13S
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147

rO~~OWING

,riLL THE lECTOR BurrER WITH 121 8-BIT BYTES

OVE~r,OwS

0ee224
001231
001232

0S5267
S0135'
S0SIee

030076

11:

INC PTAY
BNE SETUP
HALT

RETRY TO riLL THE SECTOR 8urrE~
HARD PARITY ERROR

,THE TRANsrER REQUEST 'LAG IS SET
I

ITRANsrEA DATA ,ROM THE PROGRAMS QAT A BurrER TO THE RXll SECTOR BurrER
I

0el234
01a248

113867
eee'"

176732

rILL:

MOve '(Rel+, AXCS

PRoGRA~S

DATA BurrER IS 6~ WORDS IN LENGTH

all LOOP

Figure 4-24

RXlljRXVl1 Fill Buffer Example

If an error occurs and the program executes a read error code function (Ill), a parity error
may occur for that command. The error status would not be for the error in which the read
error code function was originally required.

The DRV SEL RDY bit is only updated at the time of a read status function (101) for both
drives, and after an Initialize, depending on the status of drive O. At the termination of any
other functions it reflects the drive status of the last Read Status or Initialize command.

It is not required to load the Drive Select bit into the RXCS when the command is Fill
Buffer (000) or Empty Buffer (010).

Sector Addressing: 1-26 (No sector 0)
Track Addressing: 0-76

A power failure causing the recalibration of the drives will result in a Done condition, the
same as finishing reading a sector. However, during a power failure, RXES bit 2 (Initialize
Done) wiII set. Checking this bit will indicate a power fail condition.

Excessive use of the read status function (101) will result in drastically decreased throughput, because a read status function requires between one and two diskette revolutions or
about 250 ms to complete.

4-33

4.2.6 Error Recovery
There are two error indications given by the RXlljRXVll system. The read status function (Paragraph 4.2.3.5) will assemble the current contents of the RXES (Paragraph 4.2.2.6), which can be
sampled to determine errors. The read error code function (Paragraph 4.2.3.7) can also be used to
retrieve explicit error information. The RX 11 jRXV II interface register can be interrogated to determine the type of failure that occurred. A list of error codes follows.

NOTE
A read status function is not necessary if the DRV
RDY bit is not going to be interrogated because the
RX2ES is in the interface register at the completion
of every fundion.

Octal
Code
0010
0020
0040
0050
0070
0110
0120
0130
0140
0150
0160
0200
0220
0240

4.3

Code Meaning
Drive 0 failed to see home on Initialize
Drive I failed to see home on Initialize
Tried to access a track greater than 77
Home was found before desired track was reached
Desired sector could not be found after looking at 52 headers (2 revolutions)
More than 40 JlS and no SEP clock seen
A preamble could not be found
Preamble found but no 10 mark found within allowable time span
CRC error on what appeared to be a header. Error is not asserted
The header track address of a good header does not compare with the desired track
Too many tries for an lOAM (identifies header)
CRC error on reading the sector from the disk
RjW electronics failed maintenance mode test
Density Error

RX2U AND RXV21 PROGRAMMING INFORMATION

This section describes device registers, register and vector address assignments, programming specifications, and programming examples for the RX211 and RXV21 interfaces.
All software control of the RX211 jRXV21 is performed by means of two device registers: the command and status register (RX2CS) and a multipurpose data buffer register (RX2DB) which have been
assigned bus addresses and can be read or loaded.
The RX02 contains all the control circuitry required to read from and write on the disk and to calculate and verify the C RC. I t has a buffer large enough to hold one full sector of diskette data (128 or 256
8-bit bytes). Information is serially passed between the interface and the RX02.
A typical diskette write sequence, which is initiated by a user program, would occur in two steps:
Fin Buffer - A command to fill the buffer is moved into the RX2CS. The Go bit must be set. The
program tests for TR. When TR is detected, the program moves the desired word count into the
RX2DB. TR goes false while the word count is moved to the RX02. The program retests TR and
moves the bus address into the RX2DB. The device now requests bus mastership and DMA's one data
word at a time into the RX2DB and shifts it across the RX02 data bus serially one 8-bit byte at a time
into the sector buffer. When the word count register overflows (if necessary, the RX02 control zerofills the remainder of the sector buffer) the Done bit is set, and an interrupt will occur if the program
has enabled interrupts.

4-34

Write Sector - A command to write the contents of the sector buffer onto the disk is moved into the
RX2CS. The program tests TR and when TR is set, moves the desired sector address to the RX2DB.
TR remains false while the sector address is shifted to the RX02 control. The control retests TR and
when it is again set, moves the desireq track address register to the RX2DB. Again TR is negated. The
RX02 locates the desired track and sector and compares the diskette density against the assigned
function density and writes the contents of the sector buffer onto the disk if the densities agree. When
the write operation is completed, the Done bit is set and an interrupt will occur if the program has
enabled interrupts.
A typical disk read operation occurs in the reverse order. First, the desired track and sector are located
and the contents of the sector are read into the sector buffer (read sector). Then the contents of the
sector buffer is unloaded into memory (empty buffer). In either case, the contents of the sector buffer
are not valid if either a Power Failor Initialize follows a fill buffer or read sector function.

4.3.1 Register and Vector Addresses
The RX211/RXV21 use two registers for communicating with the host computer: the command and
status register (RX2CS) normally assigned bus address 177170 and the data buffer register (RX2DB)
normally assigned b us address 177172. The vector address is 264.
4.3.2

Status (177170) - Loading this register while the RX02 is not busy
4.3.2.1 RX2CS - Command
and with bit 0= 1 will initiate a function as described below and indicated in Figure 4-25.

Figure 4-25

RX2CS Format RX211 jRXV21

Bit No.

Description

Go - Initiates a command to RX02. This is a write-only bit.

1-3

Function Select - These bits code one of the eight possible functions described in Paragraph
4.3.3 and listed below. These are write-only bits.

Code

Function

000
001
010
oII
100
10 I
110
III

Fill Buffer
Empty Buffer
Write Sector
Read Sector
Set Media Density
Read Status
Write Deleted Data Sector
Read Error Code

U nit select - This bit selects one of the two possible disks for execution of the desired
function. This bit is readable only when Done is set, at which time it indicates the unit
previously selected. This is a read/write bit.
4-35

Done - This bit indicates the completion of a function. Done will generate an interrupt when
asserted if Interrupt Enable (RX2CS bit 6) is set. This is a read-only bit.

Transfer Request - This bit signifies that the RX211 /RXV21 needs data or has data available. This is a read-only bit.

Density - This bit determines the density of the function to be executed. This bit is readable
only when Done is set, at which time it indicates the density of the function previously
executed. This is a read/write bit.

9-10

Reserved for future use. Must be written as a zero.

RX02 - This bit is set by the interface to inform the programmer that this is an RX02
system. This is a read-only bit.

12-13

Extended address - These bits are used to declare an extended bus address. These are writeonly bits.

RX211/RXV21 Initialize - This bit is set by the program to initialize the RX211/RXV21
without initializing all devices on the Unibus. This is a write-only bit.

CAUTION
Loading the lower byte of the RX2CS will also load
the upper byte of the RX2CS.

Upon setting this bit in the RX2CS, the RX211/RXV21 will negate Done and move the
head position mechanism of both drives (if two are available) to track O. Upon completion
of a successful Initialize, the RX02 will zero the error and status register, and set Initialize
Done. It will also read sector I of track 1 on drive 0 into the buffer.
15

Error - This bit is set by the RX02 to indicate that an error has occurred during an attempt
to execute a command. This read-only bit is cleared by the initiation of a new command or
an Initialize.

4.3.2.2 RX1DB - Data Buffer Register (177172) - This register serves as a general purpose data path
between the RX02 and the interface. It may represent one of six RX02 registers according to the
protocol of the function in progress (Paragraph 4.3.3).

This register is read/write if the RX02 is not in the process of executing a command; that is, it may be
manipulated without affecting the RX02 subsystem. If the RX02 is actively executing a command, this
register will only accept data if RX2CS bit 7 (TR) is set. In addition, valid data can only be read when
TR is set.
CAUTION
Violation of protocol in manipulation of this register
may cause permanent data loss.
4-36

4.3.2.3 RXlT A - RX Track Address (Figure 4-26) - This register is loaded to indicate on which of the
1148 (0-76\0) tracks a given function is to operate. It can be addressed only under the protocol of the
function in progress (Paragraph 4.3.3). Bits 8-15 are unused and are ignored by the control.
15

NOT USED

0·114,

I I
CI'ISl0

Figure 4-26

RX2TA Format (RX21IjRXV21)

4.3.2.4 RX2SA - RX Sector Address (Figure 4-27) - This register is loaded to indicate on which of the
328 (1-26\0) sectors a given function is to operate. It can be addressed only under the protocol of the
function in progress (Paragraph 4.3.3).
15

I I

I I I I I
0

I I.

1·32.

NOT USED

CP 1 ~>ll

Figure 4-27

RX2SA Format (RX211 jRXV21)

4.3.2.5 RX2WC - RX Word Count Register (Figure 4-28) - For a double density sector the maximum
word count is 128\0. For a single density sector the maximum word count is 64\0. If a word count is
beyond the limit for the density indicated, the control asserts Word Count Overflow (bit 10 of
RX2 ES). This is a write-only register. The actual word count and not the 2's complement of the word
count is loaded into the register.
15

0128, "

Figure 4-28

RX2WC Format (RX21IjRXV21)

4.3.2.6 RX2BA - RX Bus Address Register (Figure 4-29) - This register specifies the bus address of
data transferred during fill buffer, empty buffer, and read definitive error operations. Incrementation
takes place after a memory transaction has occurred. The RX2BA, therefore. is loaded with the ad
dress of the first data word to be transferred. This is a l6-bit, write-only register (Paragraph 4.3.3).
15

II
Figure4-29

RX2BA and RX2DBFormat(RX21IjRXV~I)

4.3.2.7 RX2DB - RX Data Buffer (Figure 4-29) - All information transferred to and from the floppy
media passes through this register and is addressable only under the protocol of the function in progress (Paragraph 4.3.3).
4-37

4.3.2.8 RXlES - RX Error and Status (Figure 4-30) - This register contains the current error and
status conditions of the drive selected by bit 4 (Unit Select) of the RX2CS. This read-only register can
be addressed only under the protocol of the function in progress (Paragraph 4.3.3). The RX2ES is
located in the RX2DB upon completion of a function.

WC
OVFL

RESERVED

Figure 4-30

CRC

RESERVED
MA 1870

RX2ES Format (RX211/RXV21)

RXES bit assignments are:
Bit No.

Description

CRC Error - A cyclic redundancy check error was detected as information was retrieved
from a data field of the diskette. The data collected must be considered invalid. The RX2ES
is moved to the RX2DB, and Error and Done are asserted. It is suggested that the data
transfer be retried up to 10 times, as most errors are recoverable (soft).

Initialize Done - This bit is asserted in the RX2ES to indicate completion of the Initialize
routine which can be caused by RX02 power failure, system power failure, or programmable
or bus Initialize.

RX AC LO - This bit is set by the interface to indicate a power failure in the RX02 subsystem.

Density Error - This bit indicates that the density of the function in progress does not match
the drive density. Upon detection of this error the control terminates the operation and
asserts Error and Done.

Drive Density - This bit indicates the density of the diskette in the drive selected (indicated
by bit 8). The density of the drive is determined during read and write sector operations.

Deleted Data - This bit indicates that in the course of recovering data, the "deleted data"
address mark was detected at the beginning of the data field. The Drv Den bit indicates
whether the mark was a single or double density deleted data address mark. The data following the mark will be collected and transferred normally, as the deleted data mark has no
further significance other than to establish drive density. Any alteration of files or actual
deletion of data due to this mark must be accomplished by user software.

Drive Ready - This bit indicates that the selected drive is ready if bit 7 = 1 and all conditions
for disk operation are satisfied, such as door closed, power okay, diskette up to speed, etc.
The RX02 may be presumed to be ready to perform any operation. This bit is only valid
when retrieved via a read status function or initialize.

Unit Select - This bit indicates that drive 0 is selected if bit 8=0. This bit indicates the drive
that is currently selected.

Word Count Overflow - This bit indicates that the word count is beyond sector size. The fill
or empty buffer operation is terminated and Error and Done are set.

Nonexistent Memory Error - This bit is set by the interface when a DMA transfer is being
performed and the memory address specified in RX2BA is nonexistent.
4-38

4.3.3

Function Codes
Following the strict protocol of the individual function, data storage and recovery on the
RX211jRXV21 occur with careful manipulation of the RX2CS and RX2DB registers. The penalty for
violation of protocol can be permanent data loss.
A summary of the function codes is presented below:
000
001

010
all
100
101
110
III

Fill Buffer
Empty Buffer
Write Sector
Read Sector
Set Media Density
Read Status
Write Deleted Data Sector
Read Error Code

The following paragraphs describe in detail the programming protocol associated with each function
encoded and written into RX2CS bits 1-3 if Done is set.

4.3.3.1

Fill Buffer (000) - This function is used to fill the RX02 data buffer with the number of words
of data specified by the RX2WC register. Fill buffer is a complete function in itself: the function ends
when RX2WC overflows, and if necessary, the control has zero-filled the remainder of the buffer. The
contents of the buffer may be written on the disk by means of a subsequent Write Sector command or
returned to the host processor by an Empty Buffer command. If the word count is too large, the
function is terminated, Error and Done are asserted, and the Word Count overflow bit is set in
RX2ES.
To initiate this function the RX2CS is loaded with the function. Bit 4 of the RX2CS (Unit Select) does
not affect this function since no disk operation is involved. Bit 8 (Density) must be properly selected
since this determines the word count limit. When the command has been loaded, the Done bit (RX2CS
bit 5) goes false. When the TR bit is asserted the RX2WC may be loaded into the data buffer register.
When TR is again asserted, the RX2BA may be loaded into the RX2DB. The data words are transferred directly from memory and when RX2WC overflows and the control has zero-filled the remainder of the sector buffer, if necessary, Done is asserted ending the operation. If bit 6 RX2CS (Interrupt
Enable) is set, an interrupt is initiated. Any read of the RX2DB during the data transfer is ignored by
the interface. After Done is true the RX2ES is located in the RX2DB register.

4.3.3.2

Empty Buffer (001) - This function is used to empty the contents of the internal buffer
through the RX211 jRXV21 for use by the host processor. This data is in the buffer as the result of a
previous Fill Buffer or Read Sector command.
The programming protocol for this function is identical to that for the Fill Buffer command. The
RX2CS is loaded with the command to initiate the function. (This function will ignore bit 4 RX2CS,
Unit Select). RX2CS bit 8 (Density) must be selected to allow the proper word count limit. When the
command has been loaded, the Done bit (RX2CS bit 5) goes false. When the TR bit is asserted, the
RX2WC may be loaded into the RX2DB. When TR is again asserted the RX2BA may be loaded into
the RX2DB. The RX21ljRXV21 assembles one word of data at a time and transfers it directly to
memory. Transfers occur until word count overflow, at which time the operation is complete and
Done goes true. If bit 6 RX2CS (Interrupt Enable) is set, an interrupt is initiated. After Done is true,
the RX2ES is located in the data buffer register.

4.3.3.3

Write Sector (010) - This function is used to locate a desired sector on the diskette and fill it
with the contents of the internal buffer. The initiation of the function clears RX2ES, TR, and Done.

4-39

When TR is asserted, the program must load the desired sector address into RX2DB, which will drop
TR. When TR is again asserted, the program must load the desired track address into the RX2DB,
which will drop TR. TR will remain unasserted while the RX02 attempts to locate the desired sector.
The diskette density is determined at thi-s time and is compared to the function density. If the densities
do not agree, the operation is terminated; bit 4 RX2ES is set, RX2ES is moved to the RX2DB, Error
(bit 15 RX2CS) is set, Done is asserted, and an interrupt is initiated, if bit 6 RX2CS (Interrupt Enable)
is set.
If the densities agree but the RX02 is unable to locate the desired sector within two diskette revolutions, the interface will abort the operation, move the contents of RX2ES to the RX2DB, set Error (bit
15 RX2CS), assert Done, and initiate an interrupt if bit 6 RX2CS (Interrupt Enable) is set.
If the desired sector has been reached and the densities agree, the RX211jRXV21 will write the 12810
or 6410 words stored in the internal buffer followed by a CRC character which is automatically calculated by the RX02. The RX211jRXV2J ends the function by asserting Done and if bit 6 RX2CS
(Interrupt Enable) is set, initiating an interrupt.

CAUTION
The contents of the sector buffer are not valid data
after a power loss has been detected by the RX02.
However, write sector will be accepted as a valid instruction and the (random) contents of the buffer will
be written, followed by a valid eRe.
NOTE
The contents of the sector buffer are not destroyed
during a write sector operation.
4.3.3.4 Read Sector (011) - This function is used to locate the desired sector and transfer the contents
of the data field to the internal buffer in the control. This function may also be used to retrieve rapidly
(5 ms) the current status of the drive selected. The initiation of this function clears RX2ES, TR, and
Done.
When TR is asserted the program must load the desired sector address into the RX2DB, which will
drop TR. When TR is again asserted, the program must load the desired track address into the
RX2DB, which will drop TR.
TR and Done will remain negated while the RX02 attempts to locate the desired sector. If the RX02 is
unable to locate the desired sector within two diskette revolutions for any reason, the RXV21 jRX211
will abort the operation, set Done and Error (bit 15 RX2CS), move the contents of the RX2ES to the
RX2DB, and if bit 6 RX2CS (Interrupt Enable) is set, initiate an interrupt.

If the desired sector is successfully located, the control reads the data address mark and determines the
density of the diskette. If the diskette (drive) density does not agree with the function density the
operation is terminated and Done and Error (bit 15 RX2CS) are asserted. Bit 4 RX2ES is set (Density
Error) and the RX2ES is moved to the RX2DB. If bit 6 RX2CS (Interrupt Enable) is set, an interrupt
is initiated.
If a legal data mark is successfully located, and the control and densities agree, the control will read
data from the sector into the internal buffer. If a deleted data address mark was detected, the control
will set bit 6 RX2ES (DO). As data enters the internal buffer, a CRC is computed based on the data
field and the CRC bytes previously recorded. A non-zero residue indicates that a read error has occurred and the control sets bit 0 RX2ES (CRC error) and bit 15 RX2CS (Error). The RX211jRXV21
ends the operation by asserting Done and moving the contents of the RX2ES into the RX2DB. Ifbit 6
RX2CS is set, an interrupt is initiated.

4-40

If the desired sector is successfully located, the densities agree, and the data is transferred with no CRC
error, Done will be set and ifbit 6 RX2CS (Interrupt Enable) is set the RX211/RXV21 initiates an
interrupt.

4.3.3.5 Set Media Density (100) - This function causes the entire diskette to be reassigned to a new
density. Bit 8 RX2CS (Density) indicates the new density. The control reformats the diskette by writing new data address marks (double or single density) and zeroing all of the data fields on the diskette.

The function is initiated by loading the RX2CS with the command. Initiation of the function clears
RX2ES and Done. When TR is set, an ASCII "I" (111) must be loaded into the RX2DB to complete
the protocol. This extra character is a safeguard against an error in loading the command. When the
control recognizes this character it begins executing the command.

The control starts at sector I, track 0 and reads the header information, then starts a write operation. If
the header information is damaged, the control will abort the operation.

If the operation is successfully completed, Done is set and if bit 6 RX2CS (Interrupt Enable) is set an
interrupt is initiated.

CAUTION
This operation takes about 15 seconds and should not
be interrupted. If for any reason the operation is interrupted, an mega I diskette has been generated
which may have data marks of both densities. This
diskette should again be completely reformatted.

4.3.3.6 Maintenance Read Status (UH) - This function is initiated by loading the RX2CS with the
command. Done is cleared. The Drive Ready bit (bit 7 RX2ES) is updated by counting index pulses in
the control. The Drive Density is updated by loading the head of the selected drive and reading the first
data mark. The RX2ES is moved into the RX2DB. The RX2CS may be sampled when Done (bit 5
RX2CS) is again asserted and if bit RX2CS (Interrupt Enable) is set, an interrupt will occur. This
operation requires approximately 250 ms to complete.

4.3.3.7 Write Sector with Deleted Data (lIO) - This operation is identical to function 010 (write
sector) with the exception that a deleted data address mark is written preceding the data rather than
the standard data address mark. The Density bit associated with the function indicates whether a
single or double density deleted data address mark will be written.

4.3.3.8 Read Error Code (111) - The read error code function implies a read extended status. In
addition to the specific error code a dump of the control's internal scratch pad registers also occurs.
This is the only way that the word count register can be retrieved. This function is used to retrieve
specific information as well as drive status information depending upon detection of the general Error
bit.

4-41

The transfer of the registers is a DMA transfer. The function is initiated by loading the RX2CS with
the command and then Done goes false. When TR is true, the RX2BA may be loaded into the RX2DB
and TR goes false. The registers are assembled one word at a time and transferred directly to memory.

Register Protocol
Word 1<7:0>
Word 1< 15:8>
Word 2<7:0>
Word 2< 15:8>
Word 3<7:0>
Word 3< 15:8>
Word 4<7>
Word 4<5>
Word4<6><4>
Word 4<0>
Word 4< 15:8>

Definitive Error Codes
Word Count Register
Current Track Address of Drive 0
Current Track Address of Drive 1
Target Track of Current Disk Access
Target Sector of Current Disk Access
Unit Select Bit
Head Load Bit
Drive Density Bit of Both Drives
Density of Read Error Register Command
Track Address of Selected Drive

...

*
...*
t

* For DMA interfaces the controller status soft register is sent to the interface at the end of the command. The
four status bits are included in an 8-bit word. Unit Sele~t = bit 7, Density of Drive 1 = bit 6, Head Load = bit
5, Density of Drive 0 = bit 4, Density of Read Error Register Command = bit O.

tThe Track Address of the Selected Drive - Error is only meaningful on a code 150 error. The register contains
the address of the cylinder that the head reached on a seek error.

When the RX02 senses the return of power, it will remove Done and begin a sequence to:

1.
2.
3.
4.

Move each drive head position mechanism to track 0
Clear any active error bits
Read sector 1 of track I, on drive 0
Assert Initialize Done in the RXES.

Upon completion of the power up sequence, Done is again asserted. There is no guarantee that information being written at the time of a power failure will be retrievable; however, all other information
on the diskette will remain unaltered.

4.3.3.9 RX02 Power Fail - When the RX02 control senses a loss of power within the RX02, it will
unload the head and abort all controller action. The RXAC L line is asserted to indicate to the
RX211 jRXV21 that subsystem power is gone. The RX211 jRXV21 asserts Done and Error and sets
the RXAC L bit in the RX2ES.

4-42

4.3.4 Error Recovery
There are two error indications given by the RX211 jRXV21 system. The maintenance read status
function (Paragraph 4.3.3.6) will assemble the current contents of the RX2ES which can be sampled to
determine errors. The read error code function (Paragraph 4.3.3.8) can also be retrieved for explicit
error information. The RX211 jRXV21 interface register can be interrogated to determine the type of
failure that occurred. The error codes and their meaning are listed below.
Octal
Code

Error Code Meaning

0010
0020
0040
0050
0070
0110
0120
0130
0150
0160
0170
0200
0220
0230
0240
0250

Drive 0 failed to see home on Initialize.
Drive I failed to see home on Initialize.
Tried to access a track greater than 76
Home was found before desired track was reached.
Desired sector could not be found after looking at 52 headers (2 revolutions).
More than 40 f.1.S and no SEP clock seen
A preamble could not be found.
Preamble found but no ID mark found within allowable time span
The header track address of a good header does not compare with the desired track.
Too many tries for an IDAM (identifies header)
Data AM not found in allotted time
CRC error on reading the sector from the disk. No code appears in the ERREG.
RjW electronics failed maintenance mode test.
Word count overflow
Density Error
Wrong key word for set media density command

4.3.5

RX21ljRXV21Programming Examples

4.3.5.1 Write/Fill Buffer
Figure 4-31 illustrates a program to write data on a disk by performing write and fill buffer subroutines. Initially, the write subroutine tests to see if there is an error from the last operation. If there is
an error, a branch is made and the write subroutine is not performed; otherwise a jump is made to the
fill buffer subroutine. (Before data can be written the RX02 sector buffer must be filled.) The Fill
Buffer command is set, the density (single or double) is set, and the command is loaded in the
RX02jRXCS. After a TR is received, the word count (for either 128 or 256 bytes of data) is loaded in
the RX02jRXDB. After another TR is received, the starting address where data will be retrieved from
memory is loaded in the RX02jRXDB. The RX02 controller fills the sector buffer with the number of
bytes indicated then the RX02 controller sets the Done bit. (If an Error is detected, the Error bit is set
in the RXCS and the program halts.) The program returns to the write subroutine, the drive is selected,
the write command and interrupt enable are set, the density is set, and the command is loaded in the
RX02jRXCS. There is a wait for TR, then the sector address is loaded in the RX02jRXDB; there is
another wait for TR and the track address is loaded in the RX02jRXDB. The data loaded in the sector
buffer is written by the RX02 controller on the selected drive (disk) at the selected track and sector.
While the controller writes the data, the program waits for an interrupt (which signifies the completion
of write data) to occur in order to return to the main program.

4-43

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4-44

4.3.5.2 Read/Empty Buffer
Figure 4-32 illustrates a program to read data from the disk by performing read and empty buffer
subroutines. The drive to be read is selected, the read command and interrupt enable are set, the
density is set, and the command is loaded in the RX02/RXCS. There is a wait for TR and then the
sector address is loaded in the RX02/RXDB; there is another wait for TR, and the track address is
loaded in the RX02/RXDB. While the RX02 controller reads data from the selected location on the
selected disk into the RX02 sector buffer, the program waits for an interrupt to occur and then there is
a jump to the empty buffer subroutine. The empty buffer command is set, the density is set, and the
command is loaded into the RX02/RXCS. After a TR is received, the word count is loaded into the
RX02/RXDB; there is another wait for TR and the address in memory where the data is to be stored is
loaded into the RX02/RXDB, The data is emptied from the sector buffer by the RX02 controller, and
when the buffer is emptied, there is a return to the main program.

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Reader's Comments

RX02 FLOPPY DISK SYSTEM
USER'S GUIDE
EK-RX02-UG-OOl

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