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Document:	LT-19 Multi-Station Teletype Control Instruction Manual Volume 2
Order Number:	DEC-09-H2AB-D
Revision:
Pages:	33
Original Filename:	http://bitsavers.org/pdf/dec/pdp15/hardware/DEC-09-H2AB-D_LT19_Multi-Station_Teletype_Control_Instruction_Manual_197105.pdf

OCR Text

Digital Equipment Corporation
Maynard, Massachusetts

PDP-15 Systems
Instruction Manual
Volume 1

L T19 Multi-Station
Teletype Control

DEC-09-H2AB-D

LT19
MUL Tl-ST A TION
TELETYPE CONTROL
INST-RUCTION MANUAL

DIGITAL EQUIPMENT CORPORATION •MAYNARD, MASSACHUSETTS

1st Printing December 1968
2nd Printing May 1971

The material in this manual is for informational purposes and is subject to change
without notice.

The fol lowing are registered trademarks of Digital
Equipment Corporation, Maynard, Massachusetts:
DEC
FLIP CHIP
DIGITAL

PDP
FOCAL
COMPUTER LAB

CONTENTS
Page

CHAPTER- 1 GENERAL DESCRIPTION

1. 1

Introduction

1-1

1.2

Functional Description

1-2

1.3

LT19H Data Communications Cable Option

1-4

1.4

Programming

1-5

1.4.1

LTl9B - (1 through 5) Device Selection Codes

1-5

1.4.2

LTl9 IOT Instruction Set

1-6

l .4.3

Program Interrupts

1-7

1.5

Engineering Drawing References

1-7

1.6

Signal Mnemonics

1-7

CHAPTER 2

INSTALLATION

2. l

Installation

2-1

2.2

Power Requirements

2-1

2.3

Interface

2-3

2.4

LT19E Baud Rate Selection

2-4

2.5

Channel Assignments

2-5

2.6

Insta Ilati on Checkout

2-7

2 .6.1

LT19D Tests

2-7

2.6.2

LT19F Tests

2-7

2.6.3

LT19H Test

2-7

2.6.4

LT19H System Verification

2-8

CHAPTER 3

PRINCIPLES OF OPERATION

3.1

Block Diagram Description

3-1

3. l • 1

Transmit Operation

3-3

3.1.2

Receive Operation

3-4

3.2

Detailed Transmit Operation

3-5

3.3

Detailed Receive Operation

3-6

CHAPTER 4

MAINTENANCE

4.1

General Maintenance

4-1

4.2

LT l 9E CI ock Adjustments

4-1

4.3

Engineering Drawings

4-2

iii

ILLUSTRATIONS
Figure No.

Title

Page

1-1

LT19 System, Typical Configuration

1..2

1-2

JOT Instruction Format

1-5

2-1

Interface Connections

2-2

LT 19-Devi ce Interface Connections

2-3

3-1

LT19 Detailed Block Diagram

3-2

Transmit Operation Timing Diagram

3-5

3-3

Read Operation Timing Diagram

3-7

TABLES
Table No.

Title

Page

1-1

Differences Between Models

l-1

1-2

Related Documentation

1-3

Specification Summary

1-3

1-4

Device Select Codes

1-5

LT19 JOT Instruction

1-6

2-1

Baud Rate Selection

2-4

2-2

Channel Assignments for One LT19

2-5

2-3

Channel Assignments for Two LT19s

2-6

2-4

Channel Assignments for Three LT19s

2-6

2-5

Channel Assignment for Fourth LT19

2-7

4-1

Recommended Spare Modules

4-1

4-2

LT19 Multi-Station Teletype Control Drawing
Index List

4-2

CHAPTER 1
GENERAL DESCRIPTION

1.1

INTRODUCTION

This manual describes the LT19 Multi-Station Teletype Control used with both the PDP-9 and PDP-15
Programmed Data Processors manufactured by Digital Equipment Corporation, Maynard, Massachusetts.
The LT19 Multi-Station Teletype Control increases the basic teletypewriter facility by permitting data
transfers between the processor and any combination of up to five teletypewriters or level-operated
data terminal devices that are EIA-compatible*.
The LT19 consists of three logic subgroups:

1/0 bus interface logic; optional Teletype® control logic;

and optional EIA-level converter logic {refer to Table 1-1). Initially, this manual covered only the
A, B, and C versions of these logic subgroups. Because the D, E, and F versions are used with the
PDP-15, portions of this manual are updated to cover these models, where they differ.

Table 1-1
Differences Between Models
Logic Subgroup

PDP-9

PDP-15

Differences

Interface Logic

LT19A

LT19D

LT19D includes wiring changes
to permit separate transmit
clocks for each channel.

Teletype Control Units

LT19B

LT19E

LT19E has an additional R401
Variable Clock module for the
separate transmit clock.

EIA-level converters

LT19C

LT19F

Identical

*Logic levels specified in Electronic Industries Association (EIA) Standard RS-232C "Interconnection of
Data Terminal Equipment with a Communication Channel".
®Teletype is a registered trademark of Teletype Corporation.

1-1

Unless otherwise indicated, references in text or illustrations to LT19A, B, or C type numbers are
interchangeable with their corresponding LTl 90, E, or E type numbers. Similarly, references to
PDP-91/0 operations are valid for the PDP-15, as well.

1.2

FUNCTIONAL DESCRIPTION

Figure 1-1 shows a typical LT19 configuration utilizing three Teletypes and two EIA devices. Under
program control, the PDP-9 sends control signals, device select signals, and parallel data words to the
LT19A through the 1/0 bus. The LT19A serves as an interface and control between the PDP-91/0 bus
and a specific LT19B or LT19C unit.

1---------------------,
I
LTl9 SYSTEM
I
I

CONTROL
SIGNALS

PDP-9

PARALLEL
DATA
DEVICE
SELECT
SIGNALS

I
I
I
I
I
I
I

SERIAL
DATA

EIA

SERIAL
DATA

s~~!1-

SERIAL
DATA

L ____ _

I
I
I
I

_ _ _J

TTY

EIA

DEVICE

* CONTROL
ANY COMBINATION OF UP TO FIVE L T19B AND LT19C
UNITS MAY BE USED WITH THE LT19A.
Figure 1-1

LT19 System, Typical Configuration

Each LT19B includes the logic that comprises one Teletype control unit for operation with ASR, KSR,
RO, or SO Teletype devices. Under control of the LT19A, the LT19B converts parallel data words
from the PDP-9 to serial information which can be applied to the Teletype device. In a similar manner, the LT19B receives serial information from a Teletype and converts it to parallel data which can
be transmitted to the PDP-9.
The LT19C adds EIA-level converter logic, which permits data transfers between the PDP-9 computer
and a device using EIA levels.
Since the PDP-9 can service a device in approximately 4 !JS {one IOT instruction time), all of the
slower operating devices (TTY and EIA) can operate simultaneously and indicate a servicing requirement to the PDP-9 via the Program Interrupt Enable (PIE) facility. To allow this type of operation,
each device is assigned its own specific device code which enables the PDP-9 to address the device
when servicing is required.

1-2

This manual contains operation and maintenance information for the LT19 Multi-Station Teletype Control. Maintenance and operation descriptions for the PDP-9 are contained in the documents listed in
Table 1-2.

Table 1-2
Related Documentation
Title
PDP-9 User Handbook
or
PDP-15 User's Handbook

Document Number
F-95
DEC-15-H2DC-D
F-97

Description
Contains IOT instruction format
and program control led transfer
considerations.
Provides maintenance techniques
and IOT device selection informati on.

PDP-9 Maintenance Manual,
Volumes I and II
or
PDP-15 Maintenance Manual

DEC-15-H2BB-D

Digital Logic Handbook

C-105

Specifications and descriptions of
most FLIP CHIP modules, plus simplified explanations for selecting
and using these modules in numerous applications.

KF09A Automatic Priority
Interrupt Instruction Manual

DEC-09-15AA-D

Operation and maintenance informotion for the PDP-9 Automatic
Priority Interrupt option.

Technical manual for Model 32
and 33 ASR, KSR, and RO/SO
Teletype sets.

Teletype Bulletin 273B
Volumes I and II

Volume I contains installation,
disassembly, reassembly, lubricati on and operation documentation.
Volume II includes adjustment information on all component units
of these Teletypes.

Parts list for Model 32, and 33
ASR, KSR, and RO Teletype
sets

Teletype Bulletin 1184B

Provides complete parts documentation for these Teletypes.

LT19 Diagnostic PDP-9
PDP-15

MAINDEC-09-D8CC
MAINDEC-15-D8CA

Fault isolating maintenance program.

LT19 Diagnostic

MAIN DEC-09-D8CC-D
MAINDEC-15-D8CA-D

Program description.

Table 1-3
Specification Summary
Specification

Characteristic
Character code

5- or 8-bit* character code

Start code

1 unit start code*

*Standard Unit

1-3

Table 1-3 (Cont)
Spec ifi ca ti on. Summary
C haracteri sti c

Specification

Stop codes

1-, 1.5-, or 2-units* stop code

Operation

Full duplex

Service

Up to five units per LT19A or LT19D

Speed
LT198

10,000 baud, maximum. All units operate at the
same speed.

LT19E

Variable to 30,000 baud. See Note.

Transmission distance

2000 ft, maximum. 20 mA Current Loop only 110 baud. Maximum length of LT19H is 250 feet.

Operating temperature range

55-122 °F (15-50 °C)

Operating humidity range

10-95%

Primary power requirements

115V, 60 Hz, 250W (approx.)

*Standard Unit

NOTE
The overall speed for all LT19E channels is limited to
30,000 baud, for all N channels combined, where N = 1
to 16. This limitation is imposed so that the normal processor service routines may handle all N channels simultaneously.
Assign the highest speed channels to the first channels in
the system to keep the skip chain short. In a multiple
LT19D System, all high-speed channels must be first to
prevent a low-speed channel from locking out a highspeed unit.

1.3

LT19H DATA COMMUNICATIONS CABLE OPTION

The LT19H is a data communications cable option used for interprocessor buffer applications. It is used
between an LT19 and PTOB, between two LT19s, or between the LT19 and other devices with equivalent
interface and timing characteristics. The cable is available in five lengths:
Option

Length
(ft.)

LT19HA
LT19HB
LT19HC
LT19HD
LT19HE

50
100
150
200
250

1-4

1 .4

PROGRAMMING

Communication between the PDP-9 or PDP-15 and the LT19 units is accomplished by IOT instructions.
The keyboard and teleprinter circuits of a Teletype are considered independent devices. Therefore
each circuit is assigned a different device code to control its operation. The first Teletype has a device code of 400X assigned to its teleprinter circuit and a device code of 410X assigned to its keyboard
(or paper-tape reader) circuit.
The LT19 employs the IOT instruction format discussed in the PDP-9 and PDP-15 User Handbook. The
format example in Figure 1-2 shows the bit assignments.

OPE RAT I ON CODE

CLEAR
AC

DSO-DS5

IOPZ

o 1J2131415 sJ1 sl9l10l11l12J13l14l15l1sl11J
'---y---.J

'---v---1

'-yJ

UNUSED

SDO-SD1

IOP1

IOP4

Figure 1-2

IOT Instruction Format

The main components of the IOT instruction are as follows; four operation code bits, six device selection bits (DSO through DS5), two subdevice selection bits (SDO and SDl), and three IOP bits (IOPl, 2,
and 4). In all IOT instructions the operation code is 708 . The device selection bits identify the device selected and the type of operation to be performed. The subdevice selection bits identify theselected circuit within the LT19 and the IOP pulses initiate the required function within the selected
circuit. A 1 in bit 14 clears the processor accumulator prior to an input data transfer. Bits 4 and 5 are
not used.

1.4.1

LT19B - (1 through 5) Device Selection Codes

The IOT format for the first five LT19B units is shown in Table 1-4. The specific device select coding
for each control unit is underlined. Channel assignments for systems with more than one LT19 unit are
described in Paragraph 2 .5 of Chapter 2, Installation.

Table 1-4
Device Select Codes

Unit

Transmitter Code
(Teleprinter)

Receiver Code
(Keyboard)

LT19B-1

70400X

70410Y

LT19B-2

70402X

70412Y

(continued on next page)

1-5

Table 1-4 (Cont)
Device Select Codes

Unit

Transmitter Code
(Te Iepri nter)

Receiver Code
(Keyboard)

LT19B-3

70404X

70414Y

LT19B-4

70406X

70416Y

LT19B-5

7042ZX

7043ZY

The letter X in the transmitter codes represents either IOP l, IOP2 or IOP4. The letter Y in the receiver codes represents either IOPl or IOP2. The subdevice code for LT19B-5 (the fifth unit in each
LT19 system) is represented by the letter Zin Table 1-4 because subdevice codes have not been assigned
to this unit. The subdevice code assigned to this line is dependent upon the number of Teletypes (or
EIA devices) that are connected to the processor via the LT19 interface(s). These subdevice codes
therefore, are hand wired after the user's requirements have been determined.
Device selection and the functions performed within the LT19B units are accomplished by Wl03 Device
Selector modules which decode the device selection signals, subdevice signals and IOP pulses. The
appropriate diodes are removed from the inputs of the Wl03 modules to obtain the proper selection codes.

1.4.2

LT19 IOT Instruction Set

Table 1-5 shows the complete set of IOT instructions for the LT19 teleprinter and keyboard circuits and
identifies the function(s) of each instruction. Identical functions are performed by the LTl9- l through
LT19B-5 IOT instructions. Programming examples are provided in the PDP-15 User's Handbook, Volume 2, Chapter 4.

Table 1-5
LT19 IOT Instructions
Teleprinter Instructions
IOT

Function

704001

Skip if transmitter flag is set

704002

Clears transmitter flag

704004

Loads transmitter module and sends character to teleprinter
(continued on next page)

1-6

Table 1-5 (Cont)
LTl 9 JOT Instructions
Keyboard Instructions
Function

JOT

l .4.3

704101

Skip if receiver flag is set

704102

Reads contents of receiver module and clears receiver flag.

Program Interrupts

The LT19A or LT19D supplies API and program interrupt (PI) facilities for each of the Teletype controls.
All transmit flags are ORed together to cause interrupts on either PI or API. When API is implemented
in the processor, a transmit interrupt causes a trap to location 748 on priority level 3. A receive interrupt causes a trap to location 75 8 on priority level 3.

1.5

ENGINEERING DRAWING REFERENCES

Engineering drawings provided in Volume 2 of this manual are referenced by the letter-number combination appearing at the end of the compiete drawing designation. For exampie, drawing D-BS-L T19-A-l
is referred to as drawing A-1. Similarly, drawing D-BS-LT19B-l (sheet l of 5) is referred to as drawing B-1-1 while drawing D-BS-LT19B-l (sheet 4 of 5) is referenced as drawing B-1-4. In the LT19B
and LT19C units, sheet numbers correspond to channel numbers.

l .6

SIGNAL MNEMONICS

Uncommon signal mnemonics are explained parenthetically the first time they are mentioned in the
discussion, e.g., TSO (Teletype Serial Output).

1-7

CHAPTER 2
INSTALLATION

2.1

INSTALLATION

The LT19 system is contained within two module mounting panels of a standard PDP-9, 19-in. optional
cabinet. Complete installation consists of inserting the LT19A interfacing modules and additional
LT19B/LT19C control modules into prewired locations on the mounting panels. The LT19 operates via
program control, therefore, location on the I/O bus is not critical.
The exact number of LT19B and LT19C subsystems contained within the LT19 depends upon each user's
requirements. One LT19B subsystem is required for each Teletype and an LT19B with an LT19C is required for each EIA-level operated device. Any combination of up to five of these subsystems may be
incorporated into an LT19 system. Because device codes assigned to the LT19 will handle up to 16 devices, additional LT19 systems can be connected to the PDP-9.

2 .2

POWER REQUIREMENTS

The LT19 receives de operating power from one DEC Type 728 Power Supply. This supply is mounted on
the back door of the optional bay in which the LT19 is installed. When the PDP-9 is turned on, primary ac power from a Type 841A Power Control, mounted in the optional bay, energizes the 728 Power
Supply. In a similar manner, ac power is removed from the 728 when the PDP-9 is turned off. The
LT19 does not require any special power controls or fan assemblies other than those utilized in the
PDP-9 multibay system. The maximum load for the + lOV supply is 7 .2A and 2 .SA for the -15V supply.
The following chart indicates typical current drain for each supply for various LT19E configurations:

Number of
LT19Es

+lOV Supply
(amperes}

-15V Supply
(amperes}

1
2
3
4
5

1.47
2.88
4.30
5.72
7.14

1.58
1.86
2.14
2.42
2.70

2-1

l T I9
PDP - 9

OUT

IO SIGNAL

IO BUS 10
IO BUS ti

IO BUS 12
IO BUS I 3
IO BUS 14
IO BUS 15
IO BUS 16
IO BUS 17

825
POP~9

OUT

I 0 SYNC
IOP

IOP 2

IOP 4
SKIP RQ
PROG

INT RQ

RO RO
IO PWR CLR

A26

PDP-9

OUT

DSO

OSI
052
DS3
DS4

055
500
SD I

826

[J""

3 GR ( 1)

AP!

3 EN OUT

AP!

3 RO

API 3 EN OOT

IO ADOR 12

---<>

10 ADOR 13

IO AOOR 14
IO AODR 15
IO AODR 16

IO AODR t7
82T

APIENIN

Figure 2-1

Interface Connections

2-2

2 .3

INTERFACE

All connections between the LT19 and the PDP-9/15 Processor are made through the I/O bus, using
standard I/O bus cables. Each teletypewriter (TTY) or EIA-level device is connected to the LT19 by a
single control cable supplied with the device. The TTY cable is terminated with DEC W078A cable
connector modules that plug into assigned locations in the logic mounting panels. EIA-level devices
are connected with a data set cable, DEC part no. 70-05717.
Each LT19 receives al I I/O bus signals and sends them to the next device on the I/O bus. Figure 2-1
shows only those interface connections between the processor that are pertinent to LT19 operation. The
interface between the LT19 and its devices is shown in Figure 2-2. For additional interface information, refer to the PDP-9 User Handbook or the PDP-15 Interface Manual.

LT l 98- l

o---+--:::
M

RRE

----}DEVICE l

--0

0 '3
LTl98-2

-J

~Tso--!
PSM

DEVICE 2

RRE--<>

1
LT l 98-3

o---+.__ :::----}
M~

RRE

DEVlCE 3

--0

A02
LT19B-4

0---+--:::----}

DEVlCE 4

o - - - t - - RRE - - < >

BlO
LTl98-5
D~

0---1--

:::----}DEVICE 5

M o---+-- RRE

--0

818
TSO - TELETYPE SERIAL OUTPUT
PSM- PRINT SELECTOR MAGNET
RRE - READER RUN ENABLE

Figure 2-2

LT19-Device Interface Connections

2-3

2.4

LT19E BAUD RATE SELECTION

Each R401 Clock module provides a selectable clock frequency that is twice the baud rate for the associated channel. The doubled output frequency is required by the W706/VV707, which divides the
clock frequency by two.
To select a specific baud rate, locate the appropriate range in Table 2-1. Connect a jumper from
pin Ron the R401 to the indicated pin (L, M, N, or P). Then connect the indicated resistor (Rx) between pins Rand T. Fine tune the R401 Clock output by adjusting the internal potentiometer (Rl 1) on
the R401.
NOTE
The Rx values listed in Table 2-1 are design center
values, with 10 percent capacitor and resistor tolerances. Other values of Rx may be used if necessary.
Use the lowest value of Rx that allows adjustment to
the required frequency.
Some examples of common baud rates are:
110 baud:

Jumper pin R to L, Rx= 1.2K

2000 baud:

Jumper pin R to M, Rx = 750

2400 baud:

Jumper pin R to M, Rx = 470

11,000 baud:

Jumper pin R to N, Rx= 3.3K

30,000 baud:

Jumper pin R to P, Rx is open circuit.

Table2-1
Baud Rate Selection
Baud Rate Range

Connect Rx Between R and T

Jumper Pin R to -

59 - 106
106 - 122
116 - 146
133 - 142
137 - 146
146 - 155
155 - 161

3.3K
1.2K
1.0K
750
680
560
470

L
L
L
L
L
L
L
(continued on next page)

2-4

Table2-1 {Cont)
Baud Rate Selection
Baud Rate Range

Connect Rx Between R and T

Jumper Pin R to -

159 - 860
860 - 1297
1560 - 1795
1710 - 1910
1910 - 2084
2010 - 2150
2150 - 2265
2270 - 2400

open
3.3K
1.2K
1.0K
750
680
560
470

M
M
M
M
M
M
M
M

1590 - 8600
8600 - 12,970
15,600 - 17,950
17, 100 - 19, 100
19, 100 - 20' 840
20, 100 - 21 '500
21,500 - 22,600
22,700 - 24,000

open
3.3K
1.2K
1.0K
750
680
560
470

N
N
N
N
N
N
N
N

18,600 - 98,000*

open

*Maximum baud rate is 30,000

2.5

CHANNEL ASSIGNMENTS

Table 2-2 lists the channel assignments for one LT19 that includes from one to five channels.
NOTE
When the system includes an LT15, it becomes
logical unit number 1.

Table 2-2
Channel Assignments for One LT19
Unit No.

Transmitter Code

Receiver Code

Logical Unit No.

1
2
3
4
5

xx400x
xx402x
xx404x
xx406x
xx420x

xx410x
xx412x
xx414x
xx416x
xx430x

1
2
3
4
5

Table 2-3 lists the channel assignments for a system with two LT19s, containing up to 10 channels.

Table 2-3
Channel Assignments for Two LT19s
Unit No.

Transmitter Code

Receiver Code

Logical Unit No.

xx400x
xx402x
xx404x
xx406x
xx440x

xx410x
xx414x
xx414x
xx416x
xx450x

1
2
3
4
11

xx420x
xx422x
xx424x
xx426x
xx442x

xx430x
xx432x
xx434x
xx436x
xx452x

5
6
7
10
12

LT19 #1
1
2
3
4
5
LT19 #2
1
2
3
4
5

Table 2-4 lists the channel assignments for a system with three LT19s, containing up to 15 channels.

Table 2-4
Channel Assignments for Three LT19s
Unit No.

Transmitter Code

Receiver Code

Logical Unit No.

xx400x
xx402x
xx404x
xx406x
xx460x

xx410x
xx412x
xx414x
xx416x
xx470x

1
2
3
4
15

xx420x
xx422x
xx424x
xx426x
xx462x

xx430x
xx432x
xx434x
xx436x
xx472x

5
6
7
10
16

xx440x
xx442x
xx444x
xx446x
xx464x

xx450x
xx452x
xx454x
xx456x
xx474x

12
13
14
17

LT19 #1
1
2
3
4
5
LT19 #2
1
2
3
4
5
LT19 #3
1
2
3
4
5

2-6

For a system containing four LT19s, the channel assignments for the first three LT19 units would be the
same as listed in Table 2-4. Table 2-5 lists the channel assignment for the single channel serviced by
the fourth LT19.

Table 2-5
Channel Assignment for Fourth LT19

2.6
2 . 6. l

Unit No.

Transmitter Code

Receiver Code

Logical Unit No.

l
2
3
4
5

Not Used
Not Used
Not Used
Not Used
xx466x

Not Used
Not Used
Not Used
Not Used
xx476x

INSTALLATION CHECKOUT
LTl 9D Tests

Test each LT19 unit using program tape MAINDEC-09-DBCC-PH or -15-DBCA-PH and test procedure
MAINDEC-09-DBCC-D or -15-DBCA-D under normal +lOVand -15V margins.

2 •6 • 2

LT l 9F Tests

The LT19F EIA-level converters are intended to drive a Dataset cable or an LT19H option. To simulate
the cable and perform test procedures, add the following temporary jumpers to slot A25, A26, A27,
A28 or A29:
Jumper pin S to H
Jumper pin T to V
Jumper pin E to P (output-to-input jumper)
Then run the appropriate sections of diagnostic -09-DBCC or -15-DBCA. Remove temporary jumpers on
completion of test procedure.

2.6.3

LT19H Test

The LT19H test procedure consists of two parts. Part l is to run the LT19F tests described in Paragraph
2.6.2, with the LT19H option installed. Perform part 2 as follows:
Procedure
Insert one end of the LT l 9H cable into the appropriate output slot for
the channel under test.
(continued on next page)
2-7

Step

2.6.4

Procedure

Insert the opposite end into the unused slot A32.

Remove the jumper between pins E and P and instal I between pins A32E
and P.

Repeat test described in Paragraph 2.6.2.

LT19H System Verification

Verify the LT19H system in the field as follows:
Step

Procedure
Perform the checkout procedure described in Paragraph 2. 6. 2.

Check the opposite terminal on the data communications link. This
may be another LT19 or a PT08-F. Use MAINDEC-08-D8PA if it is
the latter.

Verify that the baud rates are identical. Then connect the LT19H
cable into both terminals of the data communications link.

Load the most recent version of the LT19 diagnostic program into the
PDP-9/15.

Instead of adding the output-to-input jumper, use a "turnaround"
program in each processor.
a.

A sample PDP-8 turnaround program is as follows:
LOC

Content

Comment

20
21
22
23
24
25
26
27

6401
5020
6406
3040
1040
7000
6416
5020

Skip on R flag
JMP .-1
Read IOT
DCA 40
TAD 40
NOP
XMIT
JMP 20

A sample PDP-9/15 turnaround program is as follows:
LOC

Content

Comment

200
201
202
203
204
205

704101
600200
704112
740000
704006
600200

Skip on R flag
JMP .-1
Read
NOP
XMIT
JMP 200
(continued on next page)

2-8

Procedure
NOTE
Both sample turnaround programs assume channel 1.
Revise IOT codes as required for each specific channel.

Check the channel as described in Paragraph 2 .6 .2.

2-9

CHAPTER 3
PRINCIPLES OF OPERATION

The LT19 system performs two types of programmed-controlled operations during which data is transferred between a processor and a Teletype or EIA device (for example, dataphone interface). A transmit
operation is performed to transfer data from a processor to a teleprinter {or EIA device) and a receive
operation is performed to transfer data from a Teletype keyboard (paper tape reader or EIA device) to a
processor.

3.1

BLOCK DIAGRAM DESCRIPTION

Figure 3-1, a detailed block diagram of the LT19 system, shows the LT19A and LT19B-1 control unit
(one of the LT19B units). the other four LT19B units (LT19B-2 through LT19B-5) are connected to the
LT19A in a similar fashion and operate in a similar manner. The LT19B-1 receives data from the Teletype keyboard via the TSO (Teletype Serial Output) line and sends data to the teleprinter via the PSM
(Print Selector Magnet) line. A signal sent to the Teletype over the RRE (Reader Run Enable) line advances the paper tape reader if the Teletype is equipped with a relay controlled paper tape reader. To
communicate with an EIA-level operated device instead of a Teletype, EIA-level converters which
change DEC standard logic levels to EIA levels are added to the control unit. The control unit is then
designated LT19C.
The transmit and receive IOT decoders are used to decode the signals on the device select, subdevice,
and IOP lines and to generate the required control signals. The control signals are sent to the transmitter and receiver modules and the IOT control register. The control register consists of three flipflops which are set to perform LT19 control functions. The flip-flops within the register are cleared by
either the CLR IOT 1 CONTROL or CLR IOT 2 CONTROL signal. These signals are initiated by an
IOPl or IOP2 pulse, respectively. They are also generated during initial processor turn-on by the IO
PWR CLR signal or whenever the IO SYNC signal is generated. Output signals from the IOT control
register generate a SKIP RQ, RD RQ, or initiate a receive operation.
LT19 system operation can be controlled via the Program Interrupt Enable (PIE) facility or the Automatic
Priority Interrupt (API) facility. In the description of the transmit or receive operations, both types of
operation are discussed.
3-1

LT19A

IOT 4301(1)
!OT 420t {1)

JOT 4161 (tl

FROM

JOT 4061 (I)

LT198-2
THROUGH
LTl9B-!i

IOT 4141 (1)
IOT 404H1)

LT 198- I

!OT 4121(1)

SKP RQ

lOT 402'11)

JOT 4001(1)
IOT 4101{1)
IDT 4102(1)
RD

JOT 4122(1) }
JOT 4t42(1)

FROM
LTl9B-2

IDT 4162 (1)

THROUGH
LT19B-5

JOT 4302(0

r- CLR IOT I CONTROL

RRE
JO PWR CLR
KEYBOARD

RECVR FLG I
CLR IDT 2 CONTROL

RECEIVER

MODULE
{W706)

IO
CONTROL
LOGIC

TSO

RECVR
FLG 1

PDP- 9
INVERTER

I
r-------I

10 BUS

INVERTER

f---+--__.

TAPE

TELETYPE

INPUT

IO PWR

10 SYNC

OR
PAPER
READER

EIA

CLRI

CONVERTER

IO SYNC

EIA
DEVICE

10-17

TELEPRINTER

PSM

10 BUS

10-17(8)

IOP1, 2 ,4

IO
PWR CL
RANSMTR

XMTR

MODULE

DSG-055

FLG I

(W707)

PROG INT RQ
500-SDI

PROG

INT RO

XMTR

AP! 3 RQ

FLG

XMTR FLG 2} FROM
XMTR FLG 3
XMTR FLG 4

f~~G~
LT19B-5

XMTR FLG 5

IO ADDA 12-17

APl 3 EN IN

RECVR

APl 3 GR (I)

LA~ ~N~o.:_ _ _ _ _ _ _

API 03 RQ (8)
NOTE
IN lT\90, THE XMTRCLK IS
LOCATED IN EACH l T19E CHANNEL

-1

09- 0150

Figure 3-1 LT19 Detailed Block Diagram

3. 1 • 1 Transmit Operation
The transmit operation is performed to print a single character on the teleprinter. An IOT 704004 instruction is used to initiate a character print on the teleprinter connected to LT19B-1. Prior to executing the instruction, the 8-bit code of the character is placed in bits 10 through 17 of the accumulator
(AC) (bits 13 through 17 for 5-bit character codes). During the execution of the instruction, the contents of the AC are present on the 1/0 bus. The signals on the IO BUS 10 through 17 lines are applied
to emitter fol lowers and the resultant signals are sent to the transmitter module 0/V707).
The device code for the IOT 704004 instruction is decoded by the transmit IOT decoder 0/V103 module}
and the IOP4 pulse produces the IOT 4004 pulse. The IOT 4004 pulse strobes the signals on the IOB
10 (B) through 17 (B) lines into the transmitter module shift register and the module shifts the character
to the teleprinter in a serial fashion via the PSM line. The rate of transfer is determined by the TCLO
clock pulse from the LT19A.
After the transfer is complete, a stop signal is placed on the PSM line, the transmitter flag is set generating the XMTR FLG 1 signal. The XMTR FLG 1 signal is sent to the transmitter flag gate generating
the XMTR FLG signal. The XMTR FLG signal conditions the transmitter API module, generating the
API 3 RQ that is sent to the processor (if a receiver flag is also raised, the receiver has a higher priority
and the XMTR EN IN signal disables the transmitter API module).
The processor detects the request and sends the API 3 GR (1) signal to the transmitter API module in the
LT19 order of priority. The API 3 GR (1) signal enables the transmitter API module sending a preset
address to the processor via the IO ADDR 12 through 17 I ines and the program executes the preset location. In this case, the program executes location 748 • The processor performs a series of IOT instructions which checks for a raised transmitter flag because the API has identified a transmitter interrupt.
When the IOT 704001 instruction is executed, the IOT 4001 signal is ANDed with the XMTR FLG 1
signal generating the IOT 4001 (1) signal. The skip request gate is enabled and the SKP RQ is generated
indicating that the next character can be sent.

If API is not used in a particular system, the PIE facility of the processor must be turned on to generate
a program interrupt. In this case, the XMTR FLG signal is inverted generating the XMTR API 03 RQ
(B) signal that is sent to the transmitter module. The PROG INT RQ is generated and sent to the processor. After detecting the PROG INT RQ, the PDP-9 enters a routine to check all its 1/0 devices for
a raised flag. When the processor executes an JOT 704001 instruction, the skip request gate is enabled
and the SKP RQ is generated and sent to the processor.
The SKP RQ causes program control to be transferred to a service routine and the next character is sent
and an JOT 704004 is performed. If the processor does not have additional data for the transmitter
module, it can clear the transmitter flag and remove the XMTR FLG l signal by performing an JOT
704002 instruction.
3-3

The XMTR FLG l signal removes the XMTR FLG signal when the IOT 704002 instruction is performed if
the XMTR FLG 2 through XMTR FLG 5 signals from the other LT19B (or LT19C) units are not present.
If one or more of these signals is present, the API 3 RQ is generated and/or PROG INT RQ remains in

the true condition. The processor must enter the appropriate checking routine to locate the raised flag
and perform the necessary service routine.

3.1.2

Receive Operation

The receiver operation is performed when the shift register in the receiver module is loaded via the
TSO line. It can be initiated in one of the following ways: a Teletype key is pressed, a paper tape
reader is enabled sending out a character, or an EIA device is enabled.
When a receive operation is initiated, a start bit appears on the TSO line, it is followed by the serial
word bits and triggers the W706 receiver module.
The presence of data on the TSO line causes the RCLE signal to enable the receiver l clock. The RCLO
signals are generated and sent to the receiver module loading the serial data into the shift register of
the module. After the last data bit is loaded, the receiver flag is set and the RECVR FLG l signal is
generated. The RECVR FLG l signal is used to generate the API 3 RQ, if API is used, and the PROG
INT RQ. These signals perform functions that are similar to the functions explained in the transmit operation with the following differences: the receiver API module causes a program execute of location
758 when it receives the API 3 GR(l) signal from the PDP-9; the PDP-9 enters a subroutine which
checks for the raised receiver flag; if the PIE facility is in use instead of API, the PDP-9 must check
all of its 1/0 devices for a raised flag.
When the IOT 704101 instruction is performed, a SKP RQ is generated by ANDing the RECVR FLG l
and IOT 4101 signals which generate the IOT 4101 (1) signal. The PDP-9 detects the SKP RQ and
transfers program control to a service routine.
To fetch the data from the receiver module, the PDP-9 performs an IOT 704102 instruction and the receiver IOT decoder generates the IOT 4102 pulse. The IOT 4102 pulse is sent to the IOT control register generating the IOT 4102 (1) signal. The IOT 4102 (1) signal enables the read request gate generating the RD RQ that enables the PDP-9 AC to accept data, transfers the data to the PDP-9 in parallel
form via the IO BUS 10 through 17 lines, and removes the RECVR FLG l signal by clearing the receiver
module flag. The API 3 RQ and/or PROG INT RQ are also removed if all RECVR FLG and XMTR FLG
signals from the other LT19B (L Tl9C) unit are cleared.

3-4

3.2

DETAILED TRANSMIT OPERATION

Figure 3-2 shows the timing sequence of a transmit operation within the LT19B-1. Engineering drawings
A-1, A-2 and B-1 are used as a reference during the following discussion.

IOT

4004 _ 3 V

_J] INITIATE.TRANSFER

INITIATE NEXT TRANSFER

__.,..

Tc L0 -

PSM

.c...:4:.:;:.0;;:..0: . : _ : N S ' - ! . e : : . : . c s ' - - - - - - - - - - - - - - - - - - - - - - - - ' · L · - - -

.,...._ 4.5 MSec/i400 NSecs

~: __.__,l_l'----'---1...__I_._I_._I_._I_._I_._I__._I__._I__.l_l'----'---1...__I_._I_._I_._I_._I_._I_._I__._I__._I__.l_l.__..__I_._I_._I_.__I_.._I__._I
ov--~

STOPI STOP2

-3V
XMTR

FLAG I

_ 3 V --------------------~

IOT
4001 11)

ov---------------------~.--5'

-u--

-3V

I µ!:"ec.

n--1u

SKIP RO _ 3 V - - - - - - - - - - - - - - - - - - - - - - - ! Y · < . . - S e _ c _ .- - - - - - !OT

4002 _ 3V

-h-- 400 NSecs.

- - - - - - - - - - - - - - - - - - - - - - - + - :_ _.,~~
-l

Figure 3-2

:- n~~ ~uEfi~~R CLR

Transmit Operation Timing Diagram

During initial processor turn-on, the IO PWR CLR pulse generates the CLR JOT l CONTROL and CLR
JOT 2 CONTROL pulses {drawing A-1) clearing the JOT control register flip-flops (B-1). The IO PWR
CLR pulse also clears the transmitter module (W707 - CD15) and the transmitter API module (Wl04 CD32).
The PDP-9 gates the character to be transferred into its AC register and onto the IO BUS 10 through 17
lines. The signals are buffered by inverters and applied to the parallel data inputs of the transmitter
module. To initiate the transfer, the PDP-9 executes an JOT 704004 instruction that is decoded by the
transmitter JOT decoder (Wl03 - CD16) generating the JOT 4004 pulse. The JOT 4004 pulse is applied
to the transmitter module gating the data into the shift register of the transmitter module. At this time,
the transmitter module is enabled to transfer the character in a serial fashion to the teleprinter via the
PSM line. Shifting commences with the first TCLO pulse following the JOT 4004 pulse. The TCLO
pulse is a 400 ns pulse generated by the XMTR clock (R401 - D09) every 4.5 ms. The frequency of the
TCLO pulse is twice the baud rate which allows for sampling each bit during the middle of the bit time.
The first bit on the PSM line is a START bit which synchronizes operation between the Teletype and the
LT19. Bit 1, which corresponds to the original information on the IO BUS 17 (B) line, is sent to the
teleprinter via the PSM line and bits 2 through 8 are shifted out in a similar manner. Jumper connections on the W707 transmitter module allow selection of either an 8-bit or 5-bit code and either a 1 .0,
1 .5 or 2 .0 unit stop code.

3-5

As data is shifted out of the register, binary Os are shifted into the other end of the register. When
the register contains all Os (after bit 8 is sampled), transfer of the character is complete and the transmitter module generates a STOP bit(s) that is sent to the teleprinter via the PSM line.
One-half unit after the STOP bit is placed on the PSM line, the XMTR FLG 1 signal is generated and
either the API or PIE facility is enabled. The operation of the PIE facility is described first.
The XMTR FLG 1 signal is sent to a NOR gate (drawing A-1) generating the XMTR FLG signal that is
inverted generating the XMTR API 03 RQ (B) signal. The XMTR API 03 RQ (B) signal is applied to the
CV terminal of the W707 module and causes the PROG INT RQ line to go to OV. After receiving the
PROG INT RQ, the PDP-9 enters a subroutine to check all its 1/0 devices for the raised flag. When
an IOT 704001 instruction is performed, the transmitter IOT decoder generates the IOT 4001 pulse that
is applied to the DCD gate at the set side of the IOT 4001 flip-flop (drawing B-1). Since the XMTR
FLG 1 signal has conditioned the DCD gate, the IOT 4001 flip-flop is set. The IOT 4001 (1) output
signal from the flip-flop is applied to a NOR gate generating a SKP RQ (drawing A-1) and causing the
PDP-9 to jump to a service routine. The IOT 4001 flip-flop is cleared by the CLR IOT 1 CONTROL
pulse that is generated by the IOPl signal.
For API, the XMTR FLG signal enables the transmitter API module (drawing A-2) sending an API 3 RQ
signal to the PDP-9 (assuming no receiver flag is set). The PDP-9 services the interrupt request by
sending the API 3 GR (1) signal to the transmitter API module in the LT19 order of priority. A 748
address is sent to the PDP-9 via the IO ADDR 12 through 15 lines. The program executes this location
and enters a routine which checks the LT19 transmitter flags. An JOT 704001 instruction causes a SKP
RQ to be generated and program control is transferred to a service routine.
At this time, the PDP-9 can send the next character by executing an JOT 704004 instruction. If it does
not have additional data for this teleprinter, it clears the XMTR FLG 1 signal by performing an JOT
704002 instruction •
The transmit operation of the other four LT19B (or LT19C) units takes place in a manner that is similar
to the LT198-1. The main difference between the units is in the transmitter JOT decoders which are
coded for their specific codes.

3.3

DETAILED RECEIVE OPERATION

Figure 3-3 shows the timing sequence of the serial input from a paper tape reader. The tape is placed
into the reader and the START lever is pressed. The paper tape is advanced one line, the content of
the line is read and shifted to the receiver module (W706 - CD18) in a serial fashion via the TSO line
(the TSO line also carries the data from the keyboard or EIA device).

3-6

The first bit on the TSO line is a START pulse that causes the RCLE pulse to go to -3V enabling the
CLK module (R401 - D19). The CLK module generates the 400 ns RCLO pulses at a 4.5 ms rate to
synchronize the incoming signals on the TSO line and load the character bits into the shift register of
the receiver module. After all character bits have been loaded, the receiver module flag is set and
the RECVR FLG 1 signal is generated.
JOT

4102 {I) _ 3 V

INITIATE TRANSFER

o v - - I- - ,
TSO

-3V
RRE

INITIATE NEXT TRANSFER

.~l_J.J._S_ec_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ____,_,_ _ _ __

START

BIT 1

BITZ

BIT 8

STOP 1 STOP 2

-3V
·av---~

RCLE
- 3V
-+I

RCLO _

I+- 4.5 MSecs.

/ i 400 NSecs.

:~ --~I~I_._I_._I_. _I~I__._I__. I__.l__.l..__.__I..__I. ___.__I_._I_._I__.___.____.___..____._.____.......__.__._

ov
RECVR

FLG 1 -3V

JOT
ov--------------------.r---------~
4101 {1) _ 3 v
..... +-- 1 JJ,Sec.

SKIP RO

- . +- t µ.Sec.

-3V----------------------'•---------~

Figure 3-3

Read Operation Timing Diagram

The function performed by the RECVR FLG 1 signal is dependent upon which interrupt facility is in
use. If the PIE facility is used, a RECVR FLG 1 signal is applied to a NOR gate (drawing A-1) generating the RECVR FLG signal. The RECVR FLG signal is inverted generating the RECVR API 03 RQ (B)
signal (drawing A-2) which enables the receiver module to generate a PROG INT RQ. After detecting
the PROG INT RQ, the PDP-9 enters a subroutine to check all I/0 devices. When an JOT 704101
instruction is performed, the receiver IOT decoder {W103 - CD17) generates the IOT 4101 pulse that
enables the DCD gate at the set side of the IOT 4101 flip-flop. Since the RECVR FLG 1 signal has
conditioned the DCD gate, the IOT 4101 flip-flop is set and the IOT 4101 (1) signal is generated.
The IOT 4101 (1) signal from the flip-flop is applied to a NOR gate {drawing A-1) generating a SKP
RQ that causes the program to enter a service routine. Flip-flop IOT 4101 is cleared when the IOPl
signal goes true generating the CLR IOT 1 CONTROL pulse.
With API, the RECVR FLG signal enables the receiver API module {W104 - CD31) if the API 3 EN IN
line is at -3V (drawing A-2) and sends the API 3 RQ signal to the PDP-9. The PDP-9 returns the API
3 GR (1) signal to the receiver API module in the LT19 order of priority. The API 3 GR (1) signal
enables the receiver API module sending a 758 address to the PDP-9 via the IO ADDR 12 through 17
I ines. The program executes location 75 8 and enters a routine that checks the receiver flags. When

the IOT 704101 instruction is performed, the SKP RQ is generated causing the program to enter a service routine.
3-7

After detecting a service require~ent, the PDP-9 executes an JOT 704102 instruction and the receiver
JOT decoder generates the JOT 4102 pulse setting the JOT 4102 flip-flop. The JOT 4102 (1) signal performs the following functions: it is sent fo the read request gate (drawing A-1) generating the RD RQ
that goes to the PDP-9 and enables its AC to receive the data from the receiver module; it is applied
to the DT terminal of the receiver module gating the data in the shift register onto the IO BUS 10
through 17 lines (if an 8-bit character is read); it is applied to the CD terminal of the receiver module
clearing the RECVR FLG l signal; and it causes the receiver module to generate the RRE pulse that advances the paper tape to the next line. The JOT 4102 flip-flop is cleared by the IOP2 signal generating
the CLR JOT 2 CONTROL pulse. The next receive operation is performed in an identical manner.
The receive operation of the other four LT19B (or LT19C) units is similar except that the receiver JOT
decoders are coded for the specific codes.

3-8

CHAPTER 4
MAINTENANCE

4. 1

GENERAL MAINTENANCE

The general maintenance practices described in the PDP-9 Maintenance Manual also apply to the LT19
System. No special data formats, status bits, programming considerations, operator control or indicators are required for the LT 19.
With the assumption that the processor is operating properly, faults within the LT19 system will be
detected by the LT19 diagnostic program. This program determines which Teletype, EIA device, or
control unit is at fault by error halts. Because of the simplicity of the system, most faults can be
localized to a few modules. Defective modules are replaced by spares to restore proper operation
while the defective module is repaired. Table 4-1 lists recommended spare modules.

Table 4-1
Recommended Spare Modules
Modules

Unit

4.2

LT19A/D

S 123 Input Bus Gate
S603 Pulse Amplifier
S 107 Inverter
Wl07 Bus Driver
Wl04 I/O Bus Multiplexer

LT19B/E

R401 Variable Clock
S203 Triple Flip-Flop
W005 Clamped Load
W078 Teletype Connector
Wl03 Device Selector

LT19C/F

W5 l l Negative Input Converter
W602 Bipolar Output Converter
(plus modules listed for LT19B/E)

LT19E CLOCK ADJUSTMENTS

The following steps are recommended to set up clocks for each channel:

4-1

Procedure
Setup and adjust the free-running transmit clock first. Baud rate selection
data is presented in Paragraph 2.4.
2

Remove the W706 Receiver module to allow the receive clock to run free.
Set the oscilloscope to ALTERNATE Sweep, INT. Trigger. Do not trigger
on CHl; this will allow the pulses from the receive clock to be matched to
the transmit clock.
NOTE
For 110-baud channels, each data bit is 9 .09 ms duration, which requires an R401 Clock to be set for 4.545
ms. Each character has 11 bits of 9.09 ms, so that '
character duration is 100 ms. Because it is difficult to
measure a c Iock i nterva I of 4. 545 ms, set up to measure an entire character of 100 ms. The oscilloscope
calibration can be checked by displaying six complete
cycles of 60 Hz in exactly 10 cm. With the oscilloscope calibrated to 100 ms, fine-tune the R401 to provide 23 clock pulses in 10 cm (22 clock pulses plus the
first pulse of the next character).

4.3

ENGINEERING DRAWINGS

A complete set of LT19 Multi-Station Teletype Control engineering drawings is provided in Volume 2 of
this manual. The drawings are under DEC revision control and are updated as required by ECOs (Engineering Change Orders). The Drawing Index List, Table 4-2, lists the drawings included in Volume 2
in the sequence that they appear.

Table 4-2
LT19 Multi-Station Teletype Control Drawing Index List
Size

Type

Title

Number
LT19D

LT19-D-0

Teletype Control, Unit Assembly

LT19-D-O

Teletype Control, Parts List

LT19-D-1

1/0 Bus Interface Logic

LT19-D-2

1/0 Bus Interface

LT19-D-3

Module Utilization
LT19E

LT19-E-l

Teletype Control Unit Channel l

LT19-E-2

Teletype Control Unit Channel 2
(continued on next page)
4-2

Table 4-2 (Cont)
LT19 Multi-Station Teletype Control Drawing Index List
Size

Type

Title

Number
LT19E (Cont)

LT19-E-3

Teletype Control Unit Channel 3

LT19-E-4

Teletype Control Unit Channel 4

LT19-E-5

Teletype Control Unit Channel 5
LT19F

LT19-F-1

Teletype Control Unit Channel 1

LT19-F-2

Teletype Control Unit Channel 2

LT19-F-3

Teletype Control Unit Channel 3

LT19-F-4

Teletype Control Unit Channel 4

LT19-F-5

Teletype Control Unit Channel 5
LT19H

7005891-0-0

Data Communications Cable

Module Circuit Schematics
B
B
B
B
B
B
B

c
D
B
B

c
B

c
c

cs
cs
cs
cs
cs
cs
cs
cs
cs
cs
cs
cs
cs
cs
cs

R401-0-1

R401 Variable Clock

S107-0-1

S107 Inverter

s123•0-1

S123 Diode Gate

S203-0-1

S203 Triple Flip-Flop

S603-0-1

S603 Pulse Amplifier

W005-0-1

W005 Clamped Loads

W078-0-1

W078 Teletype Connector

W103-0-1

W103 Device Selector

W104-0-1

W104 1/0 Bus Multiplexer Control

W107-0-1

W107 1/0 Bus Receiver Circuit

W511-0-1

W511 Negative Level Converter

W602-0-l

W602 Bi-polar Level Amplifier

W705-0-1

W705 +3.6V Integrated Circuit Power Supply

W706-0-1

W706 Teletype Receiver

W707-0-1

W707 Teletype Transmitter

4-3

Digital Equipment Corporation
Maynard, Massachusetts

printed in U.S.A.