Digital Equipment LT19 User manual

Digital Equipment Corporation
Maynard, Massachusetts
PDP-15 Systems
Instruction Manual
Volume 1
L T19 Multi-Station
Teletype Control

LT19
MUL Tl-ST A TION
TELETYPE CONTROL
INST-RUCTION MANUAL
DEC-09-H2AB-D
DIGITAL EQUIPMENT CORPORATION •MAYNARD, MASSACHUSETTS

1st Printing December 1968
2nd Printing May 1971
Copyright© 1968, 1971 by Digital Equipment Corporation
The material in this manual is for informa-
tional purposes and is subject to change
without notice.
The fol lowing are registered trademarks of Digital
Equipment Corporation, Maynard, Massachusetts:
DEC
FLIP CHIP
DIGITAL
ii
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 L Tl9 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 InstaIlati 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 CIock Adjustments
4-1
4.3
Engineering Drawings
4-2
iii

ILLUSTRATIONS
Figure No. Title Page
1-1 L
T19 System, Typical Configuration 1..2
1-2
JOT Instruction Format
1-5
2-1 Interface Connections
2-2
2-2
LT 19-Devi ce Interface Connections
2-3
3-1 LT19 Detailed Block Diagram 3-2
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
1-3
Specification Summary
1-3
1-4
Device Select Codes
1-5
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
iv

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.
Logic Subgroup
Interface Logic
Teletype Control Units
EIA-level converters
Table 1-1
Differences Between Models
PDP-9 PDP-15
LT19A LT19D
LT19B LT19E
LT19C LT19F
Differences
LT19D includes wiring changes
to permit separate transmit
clocks for each channel.
LT19E has an additional R401
Variable Clock module for the
separate transmit clock.
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 L T19B or L T19C unit.
PDP-9
CONTROL
SIGNALS
PARALLEL
DATA
DEVICE
SELECT
SIGNALS
1---------------------,
I LTl9 SYSTEM I
I I
I
I
I
I
SERIAL
DATA
SERIAL
DATA
SERIAL
DATA
EIA
SERIAL
DATA
L ____ _
TTY
1
EIA
DEVICE
I
* ANY COMBINATION OF UP TO FIVE L T19B AND LT19C
CONTROL UNITS MAY BE USED WITH THE LT19A.
I
I
I
I
I
EIA I
s~~!1- I
I
_ _ _J
EIA
DEVICE
2
Figure 1-1 L T19 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 man-
ner, the L T19B 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 require-
ment 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 Con-
trol. Maintenance and operation descriptions for the PDP-9 are contained in the documents listed in
Table 1-2.
Title
PDP-9 User Handbook
or
PDP-15 User's Handbook
PDP-9 Maintenance Manual,
Volumes I and II
or
PDP-15 Maintenance Manual
Digital Logic Handbook
KF09A Automatic Priority
Interrupt Instruction Manual
Technical manual for Model 32
and 33 ASR, KSR, and RO/SO
Teletype sets.
Parts list for Model 32, and 33
ASR, KSR, and RO Teletype
sets
LT19 Diagnostic PDP-9
PDP-15
LT19 Diagnostic
Characteristic
Character code
Start code
*Standard Unit
Table 1-2
Related Documentation
Document Number
F-95
DEC-15-H2DC-D
F-97
DEC-15-H2BB-D
C-105
DEC-09-15AA-D
Teletype Bulletin 273B
Volumes I and II
Teletype Bulletin 1184B
MAINDEC-09-D8CC
MAINDEC-15-D8CA
MAINDEC-09-D8CC-D
MAINDEC-15-D8CA-D
Table 1-3
Specification Summary
Description
Contains IOT instruction format
and program controlled transfer
considerations.
Provides maintenance techniques
and IOT device selection informa-
ti on.
Specifications and descriptions of
most FLIP CHIP modules, plus sim-
plified explanations for selecting
and using these modules in numer-
ous applications.
Operation and maintenance infor-
motion for the PDP-9 Automatic
Priority Interrupt option.
Volume I contains installation,
disassembly, reassembly, lubrica-
tion and operation documentation.
Volume II includes adjustment in-
formation on all component units
of these Teletypes.
Provides complete parts documen-
tation for these Teletypes.
Fault isolating maintenance pro-
gram.
Program description.
Specification
5- or 8-bit* character code
1 unit start code*
1-3

Table 1-3 (Cont)
Speci fi ca tion. Summary
Characteristic Specification
Stop codes
Operation
Service
Speed
LT198
LT19E
1-, 1.5-, or 2-units* stop code
Full duplex
Up to five units per LT19A or L T19D
10,000 baud, maximum. All units operate at the
same speed.
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
Operating humidity range
Primary power requirements
55-122 °F (15-50°C)
10-95%
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 proc-
essor service routines may handle all N channels simul-
taneously.
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 high-
speed 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
50
LT19HB
100
LT19HC
150
LT19HD 200
LT19HE
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 de-
vice 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
DSO-DS5
CLEAR
AC IOPZ
o 1J2131415 sJ1 sl9l10l11l12J13l14l15l1sl11J
'---y---.J '---v---1 '-yJ '-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 selec-
tion 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 de-
vice selected and the type of operation to be performed. The subdevice selection bits identify these-
lected 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.
Unit
LT19B-1
LT19B-2
Table 1-4
Device Select Codes
Transmitter Code
(Teleprinter)
70400X
-
70402X
-
1-5
Receiver Code
(Keyboard)
70410Y
-
70412Y
-(continued on next page)

Unit
LT19B-3
LT19B-4
LT19B-5
Table 1-4 (Cont)
Device Select Codes
Transmitter Code
(Te Ieprinter)
70404X
-
70406X
-
7042ZX
-
Receiver Code
(Keyboard)
70414Y
70416Y
-
7043ZY
-
The letter X in the transmitter codes represents either IOP l, IOP2 or IOP4. The letter Y in the re-
ceiver 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 L Tl9- l through
LT19B-5 IOT instructions. Programming examples are provided in the PDP-15 User's Handbook, Vol-
ume 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)
LTl9 JOT Instructions
Keyboard Instructions
JOT Function
704101 Skip
if receiver flag is set
704102 Reads contents of receiver module and clears receiver flag.
l .4.3 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 in-
terrupt causes a trap to location 758 on priority level 3.
1.5 ENGINEERING DRAWING REFERENCES
Engineering drawings provided in Volume 2 of this manual are referenced by the letter-number combin-
ation 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 draw-
ing 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 re-
quired 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 de-
vices, 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, pri-
mary 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 +lOV Supply -15V Supply
LT19Es (amperes} (amperes}
1
1.47 1.58
2 2.88 1.86
3 4.30
2.14
4 5.72 2.42
5
7.14 2.70
2-1

PDP - 9
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
I 0 SYNC
IOP !
IOP 2
IOP 4
SKIP RQ
PROG INT RQ
RO RO
IO PWR CLR
A26
PDP-9
DSO
OSI
052
DS3
DS4
055
500
SD I
826
[J""
3 GR ( 1)
AP! 3 EN OUT
AP!
3 RO
8
M
82T
IO ADOR 12
10 ADOR 13
IO AOOR 14
IO AODR 15
IO AODR 16
IO AODR t7
~ APIENIN
~
Figure 2-1
l T I 9
'"
OUT
01 05
'"
OUT
M
c 2 C6
'N
OUT
02 06
I : I I : I
API 3 EN OOT
---<>
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 alI 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 informa-
tion, refer to the PDP-9 User Handbook or the PDP-15 Interface Manual.
LT l 98- l
o---+--::: ----}DEVICE l
M RRE --0
0 '3
LTl98-2
~Tso--!
1
LT l 98-3
PSM -J DEVICE 2
RRE--<>
o---+.._ __ :::----} DEVlCE 3
M~ RRE --0
A02
LT19B-4
0---+--:::----} DEVlCE 4
o---t-- RRE --<>
H~
M~
BlO
LTl98-5
0---1-- :::----}DEVICE 5
D~
~
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 as-
sociated 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) be-
tween 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 toler-
ances. 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 Rand T Jumper Pin R
to -
59 -106
3.3K
L
106 -122
1.2K
L
116 -146 1.0K L
133 -142 750 L
137 -146 680 L
146 -155 560
L
155 - 161 470 L
(continued on next page)
2-4

Table2-1 {Cont)
Baud Rate Selection
Baud Rate Range Connect
Rx Between Rand T Jumper Pin R
to -
159 -860 open M
860 -1297 3.3K
M
1560 -1795 1.2K M
1710 -1910 1.0K M
1910 -2084 750 M
2010 -2150 680 M
2150 -2265 560 M
2270 -2400 470 M
1590 -8600 open N
8600 - 12,970
3.3K N
15,600 - 17,950 1.2K N
17, 100 - 19, 100
1.0K N
19, 100 - 20' 840 750 N
20, 100 - 21 '500 680 N
21,500 - 22,600
560 N
22,700 - 24,000 470 N
18,600 - 98,000*
open p
*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.
Unit No.
1
2
3
4
5
NOTE
When the system includes an LT15, it becomes
logical unit number 1.
Table 2-2
Channel Assignments for One LT19
Transmitter Code Receiver Code
xx400x xx410x
xx402x xx412x
xx404x xx414x
xx406x xx416x
xx420x xx430x
Logical Unit No.
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.
LT19 #1
1 xx400x xx410x 1
2 xx402x xx414x 2
3 xx404x xx414x 3
4 xx406x xx416x 4
5 xx440x xx450x
11
LT19 #2
1 xx420x xx430x 5
2 xx422x xx432x 6
3 xx424x xx434x 7
4 xx426x xx436x
10
5 xx442x xx452x
12
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.
LT19 #1
1 xx400x xx410x 1
2 xx402x xx412x 2
3 xx404x xx414x 3
4 xx406x xx416x 4
5 xx460x xx470x
15
LT19 #2
1 xx420x xx430x 5
2 xx422x xx432x 6
3 xx424x xx434x 7
4 xx426x xx436x
10
5 xx462x xx472x 16
LT19 #3
1 xx440x xx450x 11
2 xx442x xx452x 12
3 xx444x xx454x
13
4 xx446x xx456x
14
5 xx464x xx474x 17
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
Unit No. Transmitter Code Receiver Code Logical Unit
No.
l
Not Used Not Used
-
2
Not Used Not Used
-
3 Not Used Not Used -
4 Not Used Not Used
-
5 xx466x xx476x 20
2.6 INSTALLATION CHECKOUT
2. 6. l 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 l9H cable into the appropriate output slot for
the channel under test.
(continued on next page)
2-7

Step
2
3
4
Procedure
Insert the opposite end into the unused slot A32.
Remove the jumper between pins Eand P and instal I between pins A32E
and P.
Repeat test described in Paragraph 2.6.2.
2.6.4 LT19H System Verification
Verify the LT19H system in the field as follows:
Step
2
3
4
5
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.
b.
A sample PDP-8 turnaround program is as follows:
LOC Content Comment
20 6401 Skip on Rflag
21 5020 JMP .-1
22 6406 Read IOT
23 3040 DCA 40
24 1040
TAD 40
25 7000 NOP
26 6416 XMIT
27 5020 JMP 20
A sample PDP-9/15 turnaround program is as follows:
LOC
200
201
202
203
204
205
Content
704101
600200
704112
740000
704006
600200
2-8
Comment
Skip on Rflag
JMP .-1
Read
NOP
XMIT
JMP 200
(continued on next page)