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EK-LA120-TM-001

January 1980

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Document:	LA120 Technical Manual
Order Number:	EK-LA120-TM
Revision:	001
Pages:	227
Original Filename:	http://bitsavers.org/pdf/dec/terminal/la120/EK-LA120-TM-001_LA120_Technical_Manual_Jan80.pdf

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EK-LA120-TM-001

LA120
TECH N ICAl MAN UAl

digital equipment corporation • maynard, massachusetts

First Edition, January 1980

Copyright © 1980 by Digital Equipment Corporation
All Rights Reserved
The material in this manual is for informational
purposes and is subject to change without notice.
Digital Equipment Corporation assumes no responsibility for any errors which may appear in
this manual.

Printed in U.S.A.

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

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

PDP
DECUS
UNIBUS

o ECsystem-l 0
DECSYSTEM-20
DIBOL
EDUSYSTEM
VAX
VMS

MASSBUS
OMNIBUS
OS/8
RSTS
RSX

lAS

CONTENTS
Page
CHAPTER t

OPERATORS INFORMATION

1.1
1.2
1.2.1
1.2.2
1.2.3
1.2.4
1.2.5
1.2.6
1.2.7
1.2.8
1.2.9
1.2.10
1.2.11
1.3
1.4

INTRODUCTION .............................................................................................. 1-1
OPERATOR'S CONSOLE .................................................................................. 1-2
Lights ........................................................................................................... 1-2
Local Control Keys ...................................................................................... 1-4
SET-UP Keys ............................................................................................... 1-4
Control Character Keys ................................................................................ 1-5
Other Keys ................................................................................................... 1-6
Optional Numeric Keypad ........................................................................... 1-6
Power ON /OFF Switch and Voltage Selector Switch .................................... 1-6
Cover Interlock Switch ................................................................................. 1-8
Paper Adjust Knob ....................................................................................... 1-8
Tractor Adjust Knobs .................................................................................. 1-9
Carriage Adjustment Lever ........................................................................... 1-9
ALARM INDICATORS ................................................................................... 1-10
OPERATOR TESTING AND TROU BLESHOOTING ................................... 1-11

CHAPTER 2

INSTALLATION, INTERFACE, AND SPECIFICATIONS

2.1
2.1.1
2.1.2
2.1.3
2.1.4
2.2
2.2.1
2.2.1.1
2.2.1.2
2.2.1.3
2.2.1.4
2.2.1.5
2.2.1.6
2.2.1.7
2.2.1.8
2.2.1.9
2.2.1.10
2.2.1.11
2.2.1.12
2.2.1.13
2.2.1.14
2.2.2
2.2.2.1
2.2.2.2
2.2.3
2.2.4
2.2.5
2.3

INSTALLATION AND CONFIGURATION .................................................... 2-1
Unpacking and Inspection ............................................................................ 2-2
Packing Procedures ...................................................................................... 2-2
Checkout Procedure ..................................................................................... 2-5
Answerback Jumper ..................................................................................... 2-6
INTERFACE INFORMATION ......................................................................... 2-8
Interface Signals ........................................................................................... 2-8
Protective Ground ................................................................................ 2-8
Transmitted Data (TDX) ...................................................................... 2-8
Received Data (RDX) .......................................................................... 2-8
Request to Send (RTS) ......................................................................... 2-9
Clear to Send (CTS) .............................................................................. 2-9
Data Set Ready .................................................................................... 2-9
Signal Ground ...................................................................................... 2-9
Carrier Detect (RLSD) .......................................................................... 2-9
Secondary Request to Send (SRTS) ...................................................... 2-9
Speed Indicator (SPDI) ........................................................................ 2-9
Secondary Carrier Detect (SRLSD) ...................................................... 2-9
Data Terminal Ready (DTR) ................................................................ 2-9
Ring Indicator (RI) .............................................................................. 2-9
Speed Select (SPDS) ............................................................................. 2-9
EIA Interface Cables .................................................................................... 2-9
BC22A-I0, -25 .................................................................................... 2-10
BC22B-I0, -25 .................................................................................... 2-1 0
Impedance of Terminator ........................................................................... 2-10
Rise and Fall Times .................................................................................... 2-1 0
Open Circuit Voltage .................................................................................. 2-10
LA 120 SPECIFICATIONS ................................................................................ 2-10

iii

CONTENTS (Coot)
Page

CHAPTER 3

PROGRAMMER'S INFORMATION

3.1

G ENERAL .......................................................................................................... 3-1
ESCAPE SEQUENCES ....................................................................................... 3-2
Parser Program ............................................................................................ 3-2
Sequence Descriptions .................................................................................. 3-2
Printer Character Sets ........................................................................... 3-S
Active Position ..................................................................................... 3-6
Linefeed-Newline Mode ....................................................................... 3-7
Horizontal Pitch ................................................................................... 3-7
Horizontal Margins .............................................................................. 3-8
Horizontal Tabs ................................................................................... 3-8
Vertical Pitch ........................................................................................ 3-8
Form Length ........................................................................................ 3-8
Vertical Margins ................................................................................... 3-8
Vertical Tabs ........................................................................................ 3-9
Product Identification .......................................................................... 3-9
Alternate Keypad Mode ....................................................................... 3-9
CONTROL CHARACTERS ............................................................................. 3-10
Null or Delete (NULL or DEL) .................................................................. 3-10
End of Text (ETX) ...................................................................................... 3-10
End of Transmission (EaT) ........................................................................ 3-1 0
Enquiry (ENQ) ........................................................................................... 3-10
Bell (BEL) .................................................................................................. 3-11
Backspace (BS) ........................................................................................... 3-11
Horizontal Tab (HT) .................................................................................. 3-11
Line Feed (LF) ........................................................................................... 3-\\
Vertical Tab (VT) ....................................................................................... 3-\\
Form Feed (FF) .......................................................................................... 3-\1
Carriage Return (CR) ................................................................................. 3-\1
Shift In (SI) ................................................................................................. 3-\\
Shift Out (Sa) ............................................................................................. 3-\\
Data Link Escape (OLE) ............................................................................ 3-\1
Cancel (CAN) ............................................................................................. 3-1\
Substitute (SU B) ......................................................................................... 3-\1
Escape (ESC) .............................................................................................. 3-\2
APL CHARACTER SET ................................................................................... 3-12
SAMPLE FORM SETUP USING ESCAPE SEQUENCES .............................. 3-13
SYNCH RON IZA TION .................................................................................... 3-\3
Synchronization Limits .................................................... :.......................... 3-\5
Fill Time Formulas ..................................................................................... 3-15
Horizontal Movement ........................................................................ 3-\S
Vertical Movement ............................................................................. 3-\5
KEYBOARD OPERATION ............................................................................. 3-\6
A uto Repeat ............................................................................................... 3-\6
Printable Character Keys ............................................................................ 3-\6
Control Character Keys .............................................................................. 3-17
CTRL (Control) Key .................................................................................. 3-\7

3.2
3.2.1
3.2.2
3.2.2.1
3.2.2.2
3.2.2.3
3.2.2.4
3.2.2.S
3.2.2.6
3.2.2.7
3.2.2.8
3.2.2.9
3.2.2.10
3.2.2.11
3.2.2.12
3.3

3.3.1
3.3.2
3.3.3
3.3.4
3.3.S
3.3.6
3.3.7
3.3.8
3.3.9
3.3.10
3.3.11
3.3.12
3.3.13
3.3.14
3.3.15
3.3.16
3.3.17
3.4
3.5
3.6
3.6.1
3.6.2
3.6.2.1
3.6.2.2
3.7
3.7.1
3.7.2
3.7.3
3.7.4

CONTENTS (Cont)
Page
3.7.5
3.7.6
3.7.7

Optional Auxiliary Keypad ......................................................................... 3-18
BREAK Key ........... :.................................................................................. 3-18
VIEW Key .................................................................................................. 3-18

CHAPTER 4

LA120 THEORY OF OPERATION

4.1
4.1.1
4.1.2
4.1.2.1
4.1.2.2
4.1.3
4.1.4
4.1.5
4.1.6
4.1.6.1
4.1.6.2
4.1.6.3
4.1.7
4.1.7.1
4.1.7.2
4.1.8
4.1.9
4.1.10
4.1.11
4.2
4.2.1
4.2.2
4.2.3
4.2.4
4.2.5
4.2.6
4.2.7
4.2.8
4.3
4.3.1
4.3.2
4.3.3
4.4
4.4.1
4.4.2
4.4.3
4.5
4.5.1
4.5.2
4.5.3
4.5.4
4.6
4.6.1

BASIC SYSTEM CONFIGURATION ............................................................... 4-1
Microprocessor ............................................................................................ 4-1
Device Addressing ........................................................................................ 4-1
Memory Space ..................................................................................... 4-3
I/O Space ............................................................................................. 4-3
Interrupts ..................................................................................................... 4-3
ROM ........................................................................................................... 4-4
RAM ........................................................................................................... 4-5
Keyboard ..................................................................................................... 4-5
Keyboard Addressing ........................................................................... 4-5
Switch Matrix ....................................................................................... 4-7
Separately Decoded Keys ..................................................................... 4-7
Display ......................................................................................................... 4-7
LEDs ................................................................................................... 4-7
Seven Segment Display ......................................................................... 4-7
Non-Volatile Memory .................................................................................. 4-8
DC305 Printer Controller ............................................................................. 4-9
8251A USART .............................................................................................4-9
Utility I/O Ports ......................................................................................... 4-10
DC305 PRINTER CONTROLLER .................................................................. .4-10
Dot Print Control ....................................................................................... 4-1 0
Carriage Position Count ............................................................................. 4-11
Carriage Speed Control .............................................................................. 4-11
Line Feed Control ...................................................................................... 4-11
Bell Control ................................................................................................ 4-11
Frequency Generation ................................................................................ 4-11
Tick Alarm ................................................................................................. 4-11
Interrupt Vectors ........................................................................................ 4-12
LA 120 FIRMWARE OVERViEW ................................................................... .4-12
Scheduling .................................................................................................. 4-12
ROM Layout .............................................................................................. 4-12
RAM Layout .............................................................................................. 4-13
PRINT CONTROL FIRMW ARE .................................................................... .4-13
Starting the Printing Operation .................................................................. .4-13
Flight Time Compensation ........................................................................ .4-15
Dot Rate Limiting ...................................................................................... 4-15
CARRIAG E SERVO FIRMWARE ................................................................. .4-16
Transitions ................................................................................................. 4-16
Reading the Position Counter .................................................................... .4-16
Carriage Speed Command .......................................................................... 4-16
Error Conditions ........................................................................................4-16
COMMUNICATION FIRMWARE ................................................................ .4-17
Communication Modes .............................................................................. 4-17

CONTENTS (Cont)
4.6.2
4.6.3
4.6.4
4.6.5
4.6.5.1
4.6.5.2
4.6.5.3
4.6.5.4
4.6.6
4.6.6.1
4.6.6.2
4.6.6.3
4.6.6.4
4.6.6.5
4.6.6.6
4.6.7
, 4.6.7.1
4.6.7.2
4.6.8
4.6.8.1
4.6.8.2
4.6.8.3
4.6.9
4.7
4.7.1
4.7.1.1
4.7.1.2
4.7.1.3
4.7.1.4
4.7.1.5
4.7.1.6
4.7.1.7
4.7.2
4.7.3
4.7.3.1
4.7.3.2
4.7.3.3
4.7.4
4.7.5
4.7.6
4.8
4.8.1
4.8.1.1
4.8.1.2
4.8.2
4.8.3
4.9
4.9.1
4.9.2
4.9.3
4.9.4

Page
Local Mode ................................................................................................ 4-17
Disconnects ................................................................................................4-17
Full Duplex Without EIA Controls ............................................................ .4-17
Full Duplex with EIA Controls .................................................................. .4-17
Full-Duplex Break .............................................................................. 4-18
Full-Duplex Disconnect ...................................................................... 4-18
Restraint Mode .................................................................................. 4-19
Speed Control Mode ........................................................................... 4-19
Half Duplex ................................................................................................ 4-19
Initial Direction Determination ......................................................... .4-19
Reverse Channel ................................................................................. 4-19
Request to Send Delay ........................................................................ 4-19
Turnaround Characters ......................................................................4-20
Half-Duplex Break ............................................................................. 4-20
Half-Duplex Disconnect ..................................................................... 4-20
Communication State Control ................................................................... .4-21
Communication State Table ......................................... ,.................... .4-21
Communication Handler .................................................................... 4-21
Control Code Generation and Detection .................................................... .4-23
Input Scanning ................................................................................... 4-23
Transmit Scanning .............................................................................. 4-23
Control Code Generation ...................................................................4-23
Functional State Diagrams ........................................................................ .4-23
ESCAPE SEQUENCE PROCESSING ............................................................. .4-28
Escape Sequence State Transition Table ..................................................... .4-28
Element No. 1..................................................................................... 4-29
Element No. 2 ..................................................................................... 4-30
Element No. 3..................................................................................... 4-30
Element No. 4 ..................................................................................... 4-30
Element No. 5..................................................................................... 4-30
Element No. 6..................................................................................... 4-31
Element No. 7..................................................................................... 4-31
Escape Sequence Jump Table ...................................................................... 4-31
Escape Sequence Parser .............................................................................. 4-31
Begin Parsing ...................................................................................... 4-31
Initialize Parser ................................................................................... 4-32
Flow Controller .................................................................................. 4-32
CSI Parameters ........................................................................................... 4-33
Control Strings ........................................................................................... 4-33
Final Character Perform-Function Routines .............................................. .4-33
SET-UP COMMAND PROCESSING ............................................................. .4-33
SET-UP Command Implementation ........................................................... 4-34
Multiple Choice SET-UP Commands ................................................. 4-34
Immediate Action SET-UP Commands ............................................. .4-34
SET-UP Handler ........................................................................................ 4-35
SET-UP/Keyboard Handler Relationship ................................................. .4-36
CHARACTER PROCESSING ........................................................................ .4-36
Character Reception ................................................................................... 4-36
Background Executive ................................................................................ 4-36
Print Line Builder ....................................................................................... 4-37
Answerback Entry Handler ........................................................................ 4-38
vi

CONTENTS (Coot)
Page
CHAPTERS

TROUBLESHOOTING THE LA120

5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8
5.9
5.10

GENERAL .......................................................................................................... 5-1
DC SERVO TEST ............................................................................................... 5-8
ENCODER DUTY CYCLE CHECK/ADJUSTMENT ..................................... 5-9
CLOCK TEST ................................................................................................... 5-12
WAKE UP TEST ............................................................................................... 5-12
PRINT CHARACTER TEST ............................................................................ 5-14
USART TEST .................................................................................................... 5-17
KEYBOARD TEST ........................................................................................... 5-21
LINE FEED TEST ............................................................................................ 5-24
BELL TEST ....................................................................................................... 5-27

CHAPTER 6

LA120 SUBASSEMBLY REMOVAL AND INSTALLATION

6.1
6.2
6.2.1
6.2.2
6.3
6.3.1
6.3.2
6.4
6.4.1
6.4.2
6.5
6.5.1
6.5.2
6.6
6.6.1
6.6.2

GENERAL .......................................................................................................... 6-1
PRINTER HOUSING ........................................................................................ 6-1
Printer Housing Removal ............................................................................. 6-1
Printer Housing Installation ......................................................................... 6-3
PRINT HEAD ASSEMBLY ............................................................................... 6-3
Print Head Assembly Removal ..................................................................... 6-4
Print Head Assembly Installation ................................................................. 6-4
PRINT HEAD CABLE ....................................................................................... 6-5
Print Head Cable Removal ........................................................................... 6-5
Print Head Cable Installation ....................................................................... 6-5
TIMING BELT ................................................................................................... 6-6
Timing Belt RemovaL ................................................................................... 6-6
Timing Belt Installation ................................................................................ 6-6
PRINT BAR ........................................................................................................ 6-8
Print Bar RemovaL ....................................................................................... 6-8
Print Bar Installation .................................................................................... 6-8
CARRIAGE ASSEMBLY AND FRONT CARRIAGE SHAFT ........................ 6-9
Carriage Assembly and Front Carriage Shaft Removal ................................. 6-9
Carriage Assembly and Front Carriage Shaft Installation ........................... 6-11
CARRIAGE ECCENTRIC BEARING AND LEVER ..................................... 6-11
Carriage Eccentric Bearing and Lever Removal .......................................... 6-11
Carriage Eccentric Bearing and Lever Installation ....................................... 6-11
REAR CARRIAGE SHAFT AND PLAIN BUSHING .................................... 6-13
Rear Carriage Shaft and Plain Bushing Removal ........................................ 6-13
Rear Carriage Shaft and Plain Bushing Installation ..................................... 6-14
RIBBON DRIVE PULLEY ............................................................................... 6-14
Ribbon Drive Pulley Removal .................................................................... 6-14
Ribbon Drive Pulley Installation ................................................................ 6-14
RIBBON DRIVE ASSEMBLy .......................................................................... 6-15
Ribbon Drive Assembly Removal ............................................................... 6-15
Ribbon Drive Assembly Installation ........................................................... 6-17
RIBBON DRIVE FAFNIR BEARING ............................................................. 6-18
Ribbon Drive Fafnir Bearing Removal ....................................................... 6-18
Ribbon Drive Fafnir Bearing Installation ................................................... 6-18
RIBBON ECCENTRIC AND BACKSTOP SPRING ....................................... 6-19
Ribbon Eccentric and Backstop Spring Removal ........................................ 6-19

6.7
6.7.1

6.7.2
6.8
6.8.1
6.8.2
6.9
6.9.1

6.9.2
6.10
6.10.1
6.10.2
6.11
6.11.1
6.11.2
6.12
6.12.1
6.12.2
6.13
6.13.1

vii

CONTENTS (Cont)
Page

6.13.2
6.14
6.14.1
6.14.2
6.15
6.15.1
6.15.2
6.16
6.16.1
6.16.2
6.17
6.17.1
6.17.2
6.18
6.18.1
6.18.2
6.19
6.19.1
6.19.2
6.20
6.20.1
6.20.2
6.21
6.21.1
6.21.2
6.22
6.22.1
6.22.2
6.23
6.23.1
6.23.2
6.24
6.24.1
6.24.2
6.25
6.25.1
6.25.2
6.26
6.26.1
6.26.2

Ribbon Eccentric and Backstop Spring Installation .................................... 6-20
DC MOTOR AND ENCODER ASSEMBLY ................................................... 6-20
DC Motor and Encoder Assembly Removal ............................................... 6-20
DC Motor and Encoder Assembly Installation ........................................... 6-21
TRACTOR DRIVE SHAFTS AND TRACTOR ASSEMBLIES ...................... 6-22
Tractor Drive Shaft and Tractor Assembly Removal.. ................................. 6-22
Tractor Drive Shaft and Tractor Assembly Installation ............................... 6-23
IDLER GEAR ASSEMBLy .............................................................................. 6-24
Idler Gear Assembly Removal .................................................................... 6-24
Idler Gear Assembly Installation ................................................................ 6-24
STEPPING MOTOR ASSEMBLY .................................................................... 6-25
Stepping Motor Assembly Removal. ........................................................... 6-25
Stepping Motor Assembly Installation ........................................................ 6-26
RIBBON CHASSIS ASSEMBLY ...................................................................... 6-27
Ribbon Chassis Assembly Removal ............................................................ 6-27
Ribbon Chassis Assembly Installation ........................................................ 6-28
RIBBON SPOOL RATCHET WHEELS AND FRICTION DISKS .................. 6-29
Ribbon Spool Ratchet Wheel(s) and Friction Disk Removal ....................... 6-29
Ribbon Spool Ratchet Wheel(s) and Friction Disk Installation ................... 6-30
KEYBOARD/NUMERIC PAD ASSEMBLY .................................................. 6-30
Keyboard/Numeric Pad Assembly Removal .............................................. 6-30
Keyboard/Numeric Pad Assembly Installation ........................................... 6-31
POWER SUPPLY ASSEMBLY ........................................................................ 6-32
Power Supply Assembly Removal ............................................................... 6-33
Power Supply Assembly Installation ........................................................... 6-34
PRINTER MECHANISM ASSEMBLY ........................................................... 6-35
Printer Mechanism Assembly Removal.. ..................................................... 6-35
Printer Mechanism Assembly Installation ................................................... 6-35
CVT POWER SUPPLY MODULE ................................................................... 6-38
CVT Power Supply Module Removal ......................................................... 6-38
CVT Power Supply Module Installation ..................................................... 6-39
POWER ENTRY BRACKET ASSEM'BL Y ...................................................... 6-39
Power Entry Bracket Assembly Removal .................................................... 6-40
Power Entry Bracket Assembly Installation ................................................ 6-40
FAN .................................................................................................................. 6-40
Fan Removal .............................................................................................. 6-40
Fan Installation .......................................................................................... 6-40
LOGIC/POWER BOARD ................................................... ~ ............................ 6-41
Logic/Power Board Removal ..................................................................... 6-41
Logic/Power Board Installation ................................................................. 6-42

CHAPTER 7

ADJUSTMENT PROCEDURES AND LUBRICATION

7.1
7.2
7.3
7.4
7.5
7.6

PRINT HEAD ADJUSTMENT .......................................................................... 7-1
PRINTER MECHANISM ADJUSTMENT ....................................................... 7-1
PAPER GUIDE ADJUSTMENT ....................................................................... 7-4
PAPER OUT SWITCH ADJUSTMENT ............................................................ 7-5
RIBBON TENSION ADJUSTMENT ................................................................. 7-6
RIBBON DRIVE ASSEMBLY ADJUSTMENT ................................................ 7-8

viii

CONTENTS (Coot)
Page
7.7
7.8
7.9
7.10

IDLER GEAR ASSEMBLY ADJUSTMENT ................................................... 7-11
BUMPER ASSEMBLY ADJUSTMENT .......................................................... 7-12
PRINT BAR ADJUSTMENT ........................................................................... 7-13
LUBRICATION ................................................................................................ 7-15

CHAPTERS

20 rnA LAI2X-AL OPTION

8.1
8.2
8.3
8.4
8.4.1
8.4.2
8.4.3

GENERAL .......................................................................................................... 8-1
INSTALLATION ................................................................................................ 8-1
TEST AFTER INSTALLATION ........................................................................ 8-3
ELECTRICAL CHARACTERISTICS ............................................................... 8-3
Transmitter .................................................................................................. 8-3
Receiver ....................................................................................................... 8-3
Pin Assignments ........................................................................................... 8-3

CHAPTER 9

EXPANDED BUFFER OPTION LAI2X-DL

CHAPTER 10

LAI20-RE

10.1
10.2

INTRODUCTION ............................................................................................ 10-1
INSTALLATION .............................................................................................. 10-1

CHAPTER 11

LAI2X-HL KEYBOARD OPTION

11.1
11.2
11.3

INTRODUCTION ............................................................................................ 11-1
INSTALLATION .............................................................................................. 11-1
OPERATOR'S INFORMATION ..................................................................... 11-6

CHAPTER 12

LAI2X-YL OPTION

12.1
12.2
12.3
12.3.1
12.3.2
12.3.3
12.3.4
12.3.5
12.3.6
12.3.7
12.3.8
12.3.9
12.3.10
12.3.11

INTRODUCTION ............................................................................................ 12-1
INSTALLATION .............................................................................................. 12-1
OPERATOR'S INFORMATION ..................................................................... 12-7
Indicator Lights .......................................................................................... 12-7
Control Keys .............................................................................................. 12-7
SET-UP Mode ............................................................................................ 12-9
Baud Rate (Speed) .................................................................................... 12-1 0
Parity and Data Bits .................................................................................. 12-1 0
Setting Form Length ................................................................................. 12-11
Printer New Line Character ...................................................................... 12-12
Modem ..................................................................................................... 12-13
Secondary Channel ................................................................................... 12-14
Status ....................................................................................................... 12-15
Store/Recall ............................................................................................. 12-16

APPENDIX A

LA120 OPERATOR REFERENCE CARD

APPENDIX B

FACTORY PARAMETER SETTINGS

FIGURES
Figure
1-1
1-2
1-3
1-4
1-5
1-6
1-7
2-1
2-2
2-3
2-4
2-5
2-6
3-1
3-2
3-3
4-1
4-2
4-3
4-4
4-5
4-6
4-7
4-8
4-9
4-10
4-11

5-1
5-2
5-3
5-4
5-5
5-6
5-7
5-8
5-9
5-10

5-11
5-12
5-13
5-14
5-15
5-16
5-17
5-18
5-19
5-20
5-21

Title

Page

Operator's Console .............................................................................................. 1-3
Basic System Using LA120 ................................................................................... 1-3
Location of Power ON/OFF Switch and Voltage Selector Switch ......................... 1-7
Location of Cover Interlock Switch ...................................................................... 1-8
Paper Adjust Knob .............................................................................................. 1-8
Tractor Adjust Knobs .......................................................................................... 1-9
Carriage Adjustment Lever .................................................................................. 1-9
LA120 Site Considerations ................................................................................... 2-1
Unpacking/Packing ............................................................................................. 2-3
Location of Nylon Cable Tie ................................................................................ 2-4
Location ofLA120 SET-UP Label ....................................................................... 2-4
Self-Test Printout ................................................................................................. 2-6
Location of Answerback Jumper .......................................................................... 2-7
Sample Form SET-UP ........................................................................................ 3-14
Octal Codes Generated by Keyboard .................................................................. 3-16
Characters Generated by Keyboard with CTRL Key Held Down ......................... 3-8
LA120 Block Diagram ......................................................................................... 4-2
ROM Placement .................................................................................................. 4-4
RAM Address Map .............................................................................................. 4-5
Forward Print Start ............................................................................................4-14
Reverse Print Start ............................................................................................. 4-15
Note A Branch Form .......................................................................................... 4-23
Full Duplex ........................................................................................................ 4-24
Supervisory Control ........................................................................................... 4-25
Coded Control with Reverse Channel ................................................................ .4-26
Coded Control Without Reverse ChanneL ......................................................... .4-29
Entry Organization Within a Table Element ...................................................... .4-29
Logic/Power Board Connectors ........................................................................... 5-7
DC Servo Signals .................................................................................................. 5-9
Encoder Output Waveform ................................................................................ 5-1 0
Encoder Circuit Board ........................................................................................ 5-11
c/> 1 and c/>2 Clock Signals ..................................................................................... 5-12
8080A Addressing Output .................................................................................. 5-13
DC Wake Up Waveform .................................................................................... 5-13
Solenoid Signal Output of DC305 ....................................................................... 5-15
Drive Signal to Print Solenoid ............................................................................ 5-16
Head Enable vs Drive SignaL .............................................................................. 5-17
LA120 Baud Rate Clocks ................................................................................... 5-18
USART I/O Signals ........................................................................................... 5-20
Keyboard Scan Waveform .................................................................................. 5-21
Keyboard Scan Waveform with Key Pressed ...................................................... 5-22
Key Circuit Waveform ....................................................................................... 5-23
Keyboard Scan for Chip E8 ................................................................................ 5-23
Line Feed Signal Output of DC305 ..................................................................... 5-24
Line Feed Amplifier Input vs Output .................................................................. 5-25
Line Feed Run Signal ......................................................................................... 5-26
Bell Amplifier Input ........................................................................................... 5-27
Bell Amplifier Output ......................................................................................... 5-28

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

Title

Page

Assembly Removal Sequence ............................................................................... 6-2
Printer Housing Removal and Installation ............................................................ 6-3
Print Head Removal and Installation ................................................................... 6-4
Print Head Cable ................................................................................................... 6-6
Belt Tension Spring Location ............................................................................... 6-7
Belt Tension Spring (Detailed View) ..................................................................... 6-8
Carriage Assembly and Front Carriage Shaft Removal and Installation ................ 6-9
Carriage Eccentric Bearing and Lever Removal and Installation ......................... 6-12
Rear Carriage Shaft and Plain Bushing Removal and Installation ....................... 6-13
Ribbon Drive Pulley Removal and Installation ................................................... 6-15
Ribbon Drive Assembly Removal and Installation ............................................. 6-16
Ribbon Drive Assembly (Detailed View) ............................................................ 6-17
Fafnir Bearing and Ribbon Eccentric Removal and Installation .......................... 6-19
DC Motor/Encoder Assembly Removal and Installation ................................... 6-21
Tractor Drive Shaft and Tractor Assembly Removal and Installation ................. 6-22
Tractor Phasing Adjustment ............................................................................... 6-23
Idler Gear Assembly Removal and Installation ................................................... 6-24
Stepping Motor Assembly Removal and Installation .......................................... 6-25
Stepping Motor Mounted on Side Plate .............................................................. 6-26
Ribbon Chassis Assembly Removal and Installation ........................................... 6-27
Cover Interlock' Switch ..~ ..................................................................................... 6-28
Ribbon Spool Ratchet Wheel and Friction Disk Replacement ............... :............ 6-29
Keyboard/Numeric Pad Removal and Installation ............................................. 6-31
Power Supply Assembly Removal and Installation ............................................. 6-32
Power Supply Assembly in Position .................................................................... 6-34
PrinterMechanism Assembly Removal and Installation ..................................... 6-36
Cabinet Reference Holes .................................................................................... 6-37
.CVT Power Supply Module Removal and Installation ........................................ 6-38
Power Entry Bracket Assembly Removal and Installation ................................... 6-39
Fan Removal and Installation ............................................................................ 6-41
Logic/Power Board Removal and Installation .................................................... 6-42
Print Head Adjustment ........................................................................................ 7-2
Printer Mechanism Alignment .............................................................................. 7-3
Paper Guide Adjustment ...................................................................................... 7-4
Paper Out Switch Adjustment .............................................................................. 7-5
Ribbon Spool Tension Adjustment. ...................................................................... 7-6
Ribbon Threading/Drag Test. .............................................................................. 7-7
Ribbon Drive Adjustment .................................................................................... 7-9
Ribbon Drive Assembly ..................................................................................... 7-10
Idler Gear Assembly ........................................................................................... 7-11
Bumper Assembly Adjustment ........................................................................... 7-12
Print Bar Adjustment ......................................................................................... 7-14
Carriage Shaft Lubrication ................................................................................. 7-15
Ribbon Drive Assembly Lubrication .................................................................. 7-16
Installation of 20 rnA LA 12X-AL Option ............................................................. 8-2
20 rnA Current Loop Connector ........................................................................... 8-3
LAI2X-HL Keyboard ........................................................................................ 10-2
LAI2X-YL Keypad ............................................................................................ 10-3

FIGURES (Coot)
Figure No.

11-1
11-2
11-3
11-4

11-5
12-1
12-2
12-3
12-4
12-5
12-6

Title

Page

Printer Housing Removal and Installation .......................................................... 11-2
Terminator Card Removal ................................................................................. 11-3
Keyboard Cable Installation ............................................................................... 11-4
Keyboard Installation ......................................................................................... 11-5
Label Installation ............................................................................................... 11-6
Printer Housing Removal and Installation .......................................................... 12-2
Terminator Card Removal ................................................................................. 12-3
Keyboard Cable Installation ............................................................................... 12-4
Keypad Installation ............................................................................................. 12-5
Self-Test Printout ..................................................... ~ ......................................... 12-6
Form Length .................................................................................................... 12-11

TABLES
Table

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

1-5
1-6
1-7
1-8
1-9
2-1
2-2
2-3
2-4
2-5
2-6
3-1.
3-2
3-3
3-4
3-5
3-6
3-7
3-8
3-9
3-10
4-1
4-2
4-3
4-4

Title

Page

Related Documentation ....................................................................................... 1-1
LA120 Console Indicators ..................................................................................... 1-2
LA 120 Console Local Control Keys ..................................................................... 1-4
LA120 Console SET-UP Keys .............................................. ;............................... 1-4
LA 120 Console Control Character Keys ............................................................... 1-5
LA 120 Console Miscellaneous Keys ..................................................................... 1-6
Alarm Indicators ................................................................................................ 1-10
LA120 Internal Tests .......................................................................................... 1-11
Operator Troubleshooting .................................................................................. 1-11
Summary of LA 120 EIA Interface Signals ............................................................ 2-8
Printer Specifications .......................................................................................... 2-1 0
Keyboard Specifications ..................................................................................... 2-12
Communications Specifications .......................................................................... 2-13
Physical Specifications ........................................................................................ 2-14
Paper Specifications ........................................................................................... 2-15
LA 120 Escape Sequences ....................................................................................... 3-3
United States ASCII Character Set ....................................................................... 3-6
Code Differences Among National Character Sets ................................................ 3-7
Escape Sequences Transmitted in Alternate Keypad Mode ................................... 3-9
LA 120 Control Characters ................................................................................. 3-1 0
APL Character Set ..... ~ ....................................................................................... 3-12
Escape Sequences for Sample Form ............................. ~ ...................................... 3-13
Synchronization Limits ...................................................................................... 3-15
Control Character Keys ........................................................... ~ .......................... 3-17
Variations in Control Character Locations ......................................................... 3-17
LA120 Memory Read/Write Decoding ................................................................ 4-3
I/O Space Allocation ........................................................................................... 4-3
Interrupt Vectors ..................................................................................................4-4
Keyboard Addressing ........................................................................................... 4-6

xii

TABLES (Coot)
Table No.
4-5
4-6
4-7
4-8
4-9
4-10
5-1
5-2
5-3
7-1
8-1
11-1
12-1
12-2
12-3
12-4
12-5
12-6
12-7
12-8
12-9
12-10
12-11
12-12
12-13
12-14

Title

Page

LAI20LEDs ........................................................................................................ 4-7
Seven Segment Display Counter ........................................................................... 4-8
Non-Volatile Memory Operations ....................................................................... .4-8
8251A USART Ports ............................................................................................4-9
Utility I/O Ports ................................................................................................. 4-10
Disconnect Generation vs SET-UP Commands .................................................. 4-18
LA 120 Troubleshooting Procedure ....................................................................... 5-2
DC Supply Voltages ............................................................................................. 5-8
Line Feed Amplifier Test .................................................................................... 5-26
Lubrication Points .............................................................................................. 7-15
20 rnA LAI2X-AL Option Kit .............................................................................. 8-1
LAI2X-HL Installation Kit ................................................................................ ll-l
LAI2X-YL Installation Kit ................................................................................ 12-1
Printing Self-Test ................................................................................................ 12-6
Nonprinting Self-Test ......................................................................................... 12-6
Entering/Exiting SET-UP Mode ........................................................................ 12-9
Baud Rate Selection .......................................................................................... 12-10
Parity/Data Bits Selection ................................................................................ 12-11
. Form Length Selection ..................................................................................... 12-12
Carriage Return/Line Feed Responses ............................................................ .12-12
Selection of Carriage Return/Line Feed Responses .......................................... .12-13
Modem Selection .............................................................................................. 12-13
Secondary Channel Selection ............................................................................ 12-14
Status Printout Procedure ................................................................................. 12-1 5
LA120 Store Procedure ..................................................................................... 12-16
LA120 Recall Procedure ................................................................................... 12- 16

xiii

MA-2313A

LA120 DECwriter III

xiv

CHAPTER 1
OPERATORS INFORMATION
1.1 INTRODUCTION
The LAl20 DECwriter III terminal is basically a typewriter, with a wide range of features, that communicates with a computer.
The LAl20 is easily integrated into most systems. It is compatible with both EIA and ANSI standards.
Besides the many standard features built into the basic LA 120 DECwriter III, there are a number of
options and accessories that may be added to the terminal to make it useful in an even wider range of
applications.
Operator information contained in Chapter 1 is for the general user or user already familiar with the
features of a terminal.
It contains the following information:

•
•
•

Description of operator's console
Description of alarm indicators
Operator Testing and troubleshooting.

Operator information is summarized on the LAl20 Operator Reference Card (Appendix A). Table 1-1
is a list of related LA 120 documents.
Tablel-l

Related Documentation

Title

Document Number

LAl20 User Guide
LA 120 Pocket Service Guide
LAl20 DECwriter III
Illustrated Parts Breakdown

EK-LAI20-UG*
EK-LAI20-SV*
EK-LA 120-IP**

*Available on hard copy only.
** Available on hard copy and microfiche.
For information on microfiche libraries, contact:
Digital Equipment Corporation
Micropublishing Group
12 Crosby Drive
Bedford, MA 01730
Hardcopy documents can be ordered from:
Digital Equipment Corporation
444 Whitney Street
Northboro, MA 01532
Attention: Communication Services (NR2jM 15)
Customer Services Section

1-1

1.2 OPERATOR'S CONSOLE (Figure 1-1)
The LA120 operator's console contains an office typewriter-style keyboard. The keyboard contains a
four-digit numeric display and seven indicators. There is provision for an optional, field install able
numeric keypad.
To better understand the LA120 keyboard, think of the LA120 as two things. First, it is an input device
to a computer; that is, pressing a key sends information (a code) to a computer. Second, it is a printer;
information is sent from the computer to the printing portion of the LA120. However, you can set up
your system to send information from the keyboard to the printer and computer at the same time.
Figure 1-2 illustrates a basic system using an LA120.
1.2.1 Lights
The console indicator lights are listed in Table 1-2.
Table 1-2 LA120 Console Indicators
Indicator Light

Meaning

ON tJNE

The LA120 is on-line. Data is transmitted and received only while on-line.

LOCAL

The LA120 is in local mode. In local, LA120 operates as a typewriter and
does not transmit or receive data.

ALT CHAR SET

An optional alternate character set such as APL is in use.

CTS

Transmission of data is enabled (clear to send).

DSR

The modem is in data mode (data set ready).

SET-UP

Flashes to indicate that LA120 is in SET-UP mode.

PAPER OUT

Flashes to indicate that printer is not ready due to any of the following
conditions.
• Paper out
• Cover open
• Print head jam

NUMERIC DISPLAY

The numeric display indicates the next column number during normal
operation. In SET-UP mode the numeric display may also indicate line
number, baud rate, form length, etc.

1-2

NUMERIC DISPLAY
/
c=J
TAB
SET CLEAR

ON LINE LOCAL

o
CLEAR

ALTCHAR
SET

ALL

TOF

TOP
R BOT
LEFT MA RT

CTS

DSR

O·

SETUP PAPER OUT

MAR
STORE
CLEAR STATUS RECALL

BAUD

456
1
SHIFT

Figure 1-1

Operator's Console

CODE TO BE
PRINTED
COMPUTER
CODE
(GENERATED
WHEN A KEY
IS PRESSED)

MA-2306

Figure 1-2 Basic System Using LA120

1.2.2 Local Control Keys
The console local control keys and their functions are listed in Table 1-3.

Table 1-3

LA120 Console Local Control Keys

Key

Function

LINE/LOCAL

Switches the LA 120 from line to local and vice versa as indicated by ON
LINE and LOCAL lights.

HERE IS

Transmits answerback message. This key is not active in SET-UP mode.

LOCAL FORM FEED

Performs a form feed without transmitting a code to the host computer.

LOCAL LINE FEED

Advances paper one line at a time without transmitting a code to host
computer.

1.2.3 SET-UP Keys
When in SET-UP mode, most keys on the console keyboard perform a SET-UP command function.
SET-UP command functions for the top row of keys are discussed briefly in Table 1-4.
Tabie 1-4 LA120 Console Set-Up Keys
Key

Label

SET-UP

Function
Places LA120 in SET-UP mode where LA120 features can be
examined or changed. In SET-UP mode, the numeric display
indicates line number, baud rate, or form length, etc.

SET TAB

Sets a horizontal tab stop at the current column. When used
with SHIFT, sets a vertical tab stop at current line.

BOT/RT MAR

Sets right margin at current column. When used with SHIFT,
sets bottom margin at current line.

CLEAR TAB

Clears horizontal tab stop at current column. When used with
SHIFT, clears vertical tab stop at current line.

CLEAR ALL

Clears all horizontal and vertical tab stops.

TOF

Shifted or unshifted designates current paper position as top of
form. If top of form is not the same as the top margin, paper
will move to the top margin (first printable line).

MAR CLEAR

Clears left and right margins. When used with SHIFT, clears
top and bottom margins. Left or top margin becomes J. Right
or bottom margin becomes maximum allowable in the current
characters per inch (pitch) or. form length.

#£
3
$

4
&
7

1-4

Table 1-4 LA120 Console Set-Up Keys (Cont)
Key

Label

Function

STATUS

Prints a status message containing currently selected values of
SET-UP features.

(

STORE/RECALL

Recalls stored SET-UP parameters. When used with SHIFT,
stores the current SET-UP parameters.

TOP/LEFT MAR

Sets left margin at current column. When used with SHIFT,
sets top margin at current line.

BAUD

Selects receive and transmit baud rates. When used with
SHIFT, selects split transmit baud rates.

%
5
)

1.2.4 Control Character Keys
The console control character keys and their functions are listed in Table 1-5.
Table 1-5

LA120 Console Control Character Keys

Key

Function

ESC

Generates code for escape (Chapter 3).

TAB

Generates code for horizontal tab.

SPACE BAR

Generates code for space.

BACK SPACE

Generates code for backspace.

DELETE

Generates code for delete.

RETURN

Generates code for carriage return or the codes for a carriage return and line feed
sequence (in auto line feed mode). In half duplex, the RETURN key can also
generate a turnaround character in addition to its normal code or codes. The turnaround character tells the computer that it is the computer's turn to send data.

LINE FEED

Generates code for line feed.

CTRL

When held down, modifies function or codes generated by other keys.

BELL
G

Hold CTRL down and press G to generate code for the bell. G is also used in SETUP mode to change bell volume.

VT
K

Hold CTRL down and press K to generate code for vertical tab. K is also used in
SET-UP mode to turn keyclick on or off.

FF
L

Hold CTRL down and press L to generate code for form feed. L is also used in
SET-UP mode to select auto line feed.

1-5

1.2.5 Other Keys
Other miscellaneous console keys and their functions are listed in Table 1-6.
Table 1-6 LA120 Console Miscellaneous Keys
Key

Function

SHIFT

Functions the same as the shift key on a typewriter. When in SET-UP mode,
SHIFT can also be used with other keys to select LA 120 features.

CAPS LOCK

Causes alphabetic keys to transmit shift (uppercase characters) codes, regardless of
the position of the SHIFT key. CAPS LOCK does not affect numeric or other
keys.

BREAK

Causes LA120 to transmit a short break signal (233 ms). When used with SHIFT,
causes LA120 to transmit a long break disconnect signal (3.5 seconds).

VIEW

Allows operator to view last character printed.

1.2.6 Optional Numeric Keypad
The numeric keypad allows numbers to be entered in adding machine fashion. Each number key,
minus key, and comma key, normally generate the same codes as the corresponding unshifted keys on
the main keyboard. The SHIFT key does not affect the numeric keypad.
In the alternate keypad mode, the keys generate escape sequences that may have special meanings
(Chapter 3). The PF1, PF2, PF3, and PF4 keys generate escape sequences that may have special
meanings (Chapter 3). The ENTER key normally corresponds to the RETURN key. In alternate
keypad mode, ENTER generates an escape sequence that may have a special meaning (Chapter 3).
1.2.7 Power ON/OFF Switch and Voltage Selector Switch
The power switch controls power application to the LA 120. The switch is located on the LA 120 lower
front panel (Figure 1-3a). Terminals currently being manufactured also contain a voltage selector
switch. The voltage selector switch is located above the power ON /OFF switch. Place the tip of a pen
into the selector switch indentation and select the appropriate voltage, as shown in Figure 1-3b.
CAUTION
Failure to set the switch to 230 V when plugging the
LA120 into a 180-256 V power source will damage
the power supply.

1-6

POWER
ON/OFF
SWITCH
AC LINE
FUSE

a. Power ON IOFF Switch

t
115V
MOVE
SWITCH
UP

VOLTAGE
SELECTOR
SWITCH

b. Voltage Selector Switch
(Newer Terminals Only)
MA·4506

Figure 1-3 Location of Power ONIOFF Switch and
Voltage Selector Switch

1-7

1.2.8 Cover Interlock Switch
This switch is a safety feature that prevents operation of the LA 120 when the cover is open. The
location of the switch is shown in Figure 1-4.
1.2.9 Paper Adjust Knob (Figure 1-5)
The paper adjust knoq advances the paper 1/12 of an inch at a time. Pressing in and turning the paper
adjust knob enables the paper to be rolled freely in either direction and allows precise vertical forms
positioning.
NOTE
This knob should only be used when setting up the
form. To advance paper, use LOCAL LINE FEED
or LOCAL FORM FEED.

COVER INTERLOCK
SWITCH (UNDER
COVER)
~

~~I~P=====il.l\

1\
MA-4510

Figure 1-4

Location of Cover Interlock Switch

Figure 1-5

Paper Adjust Knob

1-8

1.2.10 Tractor Adjust Knobs (Figure 1-6)
The tractor adjust knobs allow fine horizontal adjustment of forms.
1.2.11 Carriage Adjustment Lever (Figure 1-7)
The carriage adjustment lever controls the print head gap for single or multipart forms.
TO FEED PINS

LEFT TRACTOR
ADJUSTING KNOB

Figure 1-6 Tractor Adjust Knobs

Figure 1-7 Carriage Adjustment Lever

1-9

MA-2309

1.3 ALARM INDICATORS
The LA120 produces several different alarm and bell signals. The operator should become familiar
with these signals to determine the correct response. Table 1-7 lists the various types of alarms, the
.
causes, and the corrective action that should be taken.
Table 1-7

Alarm Indicators

Indicator

Cause

Action/Comments

Bell and Flashing PAPER
OUT

Paper out

Load paper. Printer will resume normal operation
after paper is loaded and cover is closed.
NOTE
When out of paper, bell
will turn off after 5 seconds. If PAPER OUT
light continues to falsh after cover is closed, paper
fault still exists.

Bell only (Low
Pitch Bell
Tones)

Bell only (High
Pitch Bell
Tones)

Head Jam

Open top cover and clear obstruction causing head
jam (see Operator Troubleshooting, Table 1-9).
Reload paper by aligning perforation with print
head line indicator. Close cover.

Cover open

(Flashing light only.) Close cover.

Keyboard buffer overflow

Typing faster than the communication line can
handle will cause a buffer overflow. This condition
is indicated by a bell tone each time a key is
pressed. Under these conditions, data will not be
lost.

Input buffer overflow

Inputs to LA 120 faster than 1200 baud (without
XON /XOFF or its equivalent) can cause a buffer
overflow. This condition is indicated by a bell tone,
a special symbol printout, and loss of data.

Approaching right margin

One bell tone occurs when print head moves to
within 10 characters of right margin.

Bell character

Each bell character code received causes a bell
tone.

Invalid SET-UP command

One bell tone occurs for each invalid SET -UP command.

Incorrect entry of answerback message

Attempting to enter more than a 30 character answerback message will cause a bell tone.

(
1-10

1.4 OPERATOR TESTING AND TROUBLESHOOTING
The LA120 automatically runs several internal tests and displays the error test results in the numeric
display. Table 1-8 lists the error test results, the cause, and the required corrective action.
Table 1-8 LA120 Internal Tests
Test Result
o(flashing)
1 (flashing)
2 (flashing)
3 (flashing)
4 (flashing)
5 (flashing)
6 (flashing)
7 (flashing)
8 (flashing)
9 (flashing)
8888 (constant)

Cause
Error at ROM address 0
Error at ROM address 2048
Error at ROM address 4096
Error at ROM address 6144
Error at ROM address 8192
Error at ROM address 10240
Reserved for future options
RAM diagnostic failure
Microprocessor failure
Nonvolatile memory failure
Cover open
Out of paper

Corrective Action
Call for service
Call for service
Call for service
Call for service
Call for service
Call for service
Call for service
See Note 1
See Note 2
Close cover
Reload paper

NOTES
Turn LA120 off, then back on. If an error indication reappears, record indiction and call for
service.

If the original problem was a flashing 9, check
stored SET-UP feature to ensure that it has not
been affected. The self-test is an additional test
(Paragraph 2.1.3) that can be initiated by the
operator. The test will help determine if the
problem is in the printer or in some other portion of the communication system.

If you are unable to turn the printer.on or if the
printer appears to be faulty, refer to the operator's troubleshooting table (Table 1-9). This
table describes those things an operator can
check prior to requesting service.
Table 1-9 Operator Troubleshooting

Symptom

Possible Cause and Corrective Action

LA120 does not turn on when
printer power switch is set to
ON.

AC power cord is not plugged into wall outlet or front of printer.
Plug in cord.
Power is not coming from wall outlet. Check outlet with a known
working electrical device (such as a lamp). If no power, call maintenance personnel.
AC line fuse blown; turn printer off and replace fuse (Figure 1-3).

1-11

Table 1-9

Operator Troubleshooting (Cont)

Symptom

Possible Cause and Corrective Action

Characters do not print

Prmter out of paper; load paper. (See LA 120 User Guide for papt:r
loading.)
Printer cover open or ajar. Close cover.
Print head too far from paper; readjust carriage adjustment lever.
(See Paragraph 1.2.11 for adjustment.)
Data set unplugged; plug it in.
Incorrect communication setup.

Light print

Print head too far from paper; readjust carriage adjustment lever.
Ribbon out of ink; turn ribbon over or replace ribbon. (See LA120
User Guide for ribbon replacement.)
NOTE
Turn ribbon over after 5 to 6 hours
of continuous printing. Ribbon can
be turned over only once; then it
must be replaced.

Paper does not advance

Paper not loaded properly; check that tractor covers are closed
and feed holes are aligned properly.
Feed holes torn; reload paper. If paper falls against tractor pins or
bows in the middle, readjust right tractor.

Paper tearing on multipart
forms

Print head exerting too much pressure on paper; readjust carriage
adjustment lever.
Tractor incorrectly adjusted. If paper pulls against tractor pins or
bows in the middle, readjust right tractor.
Paper not straight in printer; realign paper.

Print head jam or print head
does not move

Paper or print head jam; clear jam and perform reloading paper/form procedure. (See LA120 User Guide.)

No keyboard or printer

Printer cover open or ajar when printer is turned on (normally
indicated by flashing 8888 and PAPER OUT light); close the
cover.

Garbled or double characters.

Incorrect communication setup. Ensure that communication setup
is compatible with the equipment at the other end of the line.

1-12

CHAPTER 2
INSTALLATION, INTERFACE,
AND SPECIFICATIONS
2.1 INSTALLATION AND CONFIGURATION
This section contains step-by-step procedures for unpacking, cabling, and unit checkout to ensure that
the unit was not damaged during shipment and that the unit is operating properly prior to connection
to the communication system.
The LA 120 should be installed in an area that is free of excessive dust, dirt, corrosive fumes, and
vapors. To ensure that the unit has proper ventilation and cooling, ventilation openings on the side of
the cabinet should not be obstructed.
A minimum 4-inch clearance between units must be maintained at all times. Figure 2-1 illustrates site
considerations.
NOTE
Site plans are not supplied by Digital Equipment
Corporation.

27.5"

i(699m m

rfrrr<

r
I --

----------..,1I
I

OPTIONAL 12.0"
PAPER
BASKET
(305mm)

U'I

.~ __

,1 I 24.0"

~____~JOmml

33.5"
(851m m)

I
I

f-----...

L21.7"
(551mm)

-J

L25.0"
(635mm)

I OPERATOR

I
I

IL __________
AREA
JI
MA3383

Figure 2-1

LA120 Site Considerations

2-1

2.1.1

Unpacking and Inspection
1.

Cut nylon retaining straps from around the shipping carton and discard them.

Remove outer cardboard shipping container.

Remove all shock-absorbing material and packing from around the LAI20 (Figure 2-2).

Loosen and remove hex-head bolts that secure wood leg brace to skid assembly. Remove
microfoam around each leg of the LA120.

Carefully inspect LA120 cabinet and carriage assembly for possible shipping damage. Inspect and check enclosed packing list for lost or missing items. Report any damaged or
missing items to the local DIGITAL Field Service or Sales Office and local carrier.

Remove printer from wooden shipping skid and place it in desired location.

Install and adjust leveling feet on LA 120 legs.

Lift LA120 top cover assembly. Clip and remove nylon cable tie securing print head assembly (Figure 2-3).

If necessary, wipe all outer surfaces with a clean, soft, lint-free cloth.

10.

Connect EIA interface cable to user's equipment.

11.

The LA120 SET-UP label is enclosed in the package with the user guide. Fasten label to area
shown in Figure 2-4.

NOTE
To install 20 mA option, refer to Chapter 8. Interface logic connections must be specified and provided
by the system supplier or the customer as each installation may differ.
2.1.2 Packing Procedures
If it is necessary to ship your LA120 to another location, repack it per the following procedure.
1.

Remove ribbon and paper.

Use a nylon cable tie to secure print head assembly (Figure 2-3). This prevents movement
during transit.

Pack LA120 as shown in Figure 2-2.

2-2

NYLON
RETAINING
STRAP---

FUll
TELESCOPE
CAP

STITCHED
TUBE
---....-.I

POlYBAG - - - -__~

1 _ - ' - - - - TERMINAL

WOOD BRACE
I
I
I

HEX-HEAD BOLTS

MICROFOAM

WOOD SKID

TEE NUTS ~--

MA-3166

Figure 2-2

Unpacking/Packing

2-3

Figure 2-3

Location of Nylon Cable Tie

N
I

REC
XMT
A
B
C
D
E
F
G
H

J
K
L
M

N
0
P
Q

R
S
U
V

W
X
Y

Z
I
T

Receive baud rate
Transmit baud rate
Auto-answerback
O=Off
1=On
Buffer control
o= Small 1 = Large
Printer char. set
1=US
2=GB
Auto-dlsconnect
o= Off 1=On
Local echo
o= Off 1=On
Form length
Unes per form
8ellvolume
O=low
1 = High
Horizontal pitch
Char. per loch
Auto-newline
O=Off
1=On
Key click
O=Off
1=On
Auto-llnefeed
O=Off
1=On
Modem/protocol
Keyboard char. set 1=US
2=GB
Alt. char. set
O=Off
1=On
Parity/data bits
HDX Initial state
O=XMT 1=REC
Auto-repeat
O=Off
1=On
Secondary channel 0 = No
1 = Yes
Break enable
O=No
1 = Yes
Vertical pitch
Unes per loch
Printer NL char.
1 = None 2=LF 3=CR
XON/XOFF
O=Nb
1 = Yes
Alt keypad mode
O=No
1 = Yes
Auto-view
O=Off
1=On
Initialize to factory settings
Selft"t: Type a character to stop
MA-2307

Figure 2-4 Location of LA120
SET-UP Label

2.1.3 Checkout Procedure
The checkout procedure consists of running the self-test exercise. Two self-tests are provided. One
prints out characters within the currently selected margins; the other causes the LA120 to go through
the same motions as the printing test, but without printing. Use the nonprinting self-test if your printer
is loaded with valuable forms such as checks or tickets.
To perform the checkout, proceed as follows.

Install ribbon and paper. (Refer to LA120 User Guide for ribbon and paper installation
procedure.)

The LA120 terminal may have a voltage selector switch located above the power ON/OFF
switch. If so, place the tip of a pen into the selector switch indentation and select the appropriate voltage (Figure 1-3b).
CAUTION
Failure to set the switch to 230 V when plugging the
LA120 into a 180-256 V power source will damage
the power supply.

Connect LA120 line cord to correct wall receptacle.
CAUTION
Before connecting LA120 to a power source, ensure
that power switch is OFF and line voltage and frequency are compatible with machine power requirements.

Set power switch to ON. Print head automatically positions itself to the left margin.

Enter SET-UP mode. SET-UP light flashes to indicate you are in SET-UP mode.

Press T to initiate a printing self-test. LA120 prints out self-test pattern (Figure 2-5).
NOTE
To run a nonprinting self-test, do not press T. Instead, press and hold SHIFT and press ~. The
LA120 will perform a nonprinting self-test.

To stop test, exit SET-UP mode or press any character. Self-test terminates.

Exit SET-UP mode. SET-UP light stops flashing.

2-5

·,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\
·-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]
·./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]10123456789:;<=)1@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]-_
'0123456789:;<=)?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]-_'
)123456789:;<=)?@ABCDEFGHIJKLMNbpaRSTUVWXYZ[\J~_'a

.23456789:;<=)?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]-_'ab
!J456789:;<=)?@ABCDEFGHIJKLMNOpaRSTUVWXYZ[\J~_'abc
~456789:;<=>?@ABCDEFGHrJKLMNOPQRSTUVWXYZ[\]-_'abcd
l56789:;<=>1@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]~_'abcde

i6789:;<=>1@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]-_'abcdef
;789:;<~>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\J~_'abcdef~
MA·4695

Figure 2-5

Self-Test Printout

2.1.4 Answerback Jumper
To obtain a permanent answerback message that cannot be changed by the operator, remove the
jumper shown in Figure 2-6.

NOTE
The answerback message must be stored in permanent memory prior to removing the jumper. When
the jumper is removed, the answerback message cannot be altered or erased.

To remove the jumper, proceed as follows.
1.
2.
3.
4.
5.

Store answerback message, if required.
Verify answerback message.
Turn power off.
Remove jumper.
Turn power on.

2-6

EIA CONNECTOR
ANSWER BACK
JUMPER
(NORMALLY BROWN
WITH A BLACK STRIP)

Figure 2-6

MA-2318

Location of Answerback Jumper

2-7

2.2 INTERFACE INFORMATION
The LA 120 interfaces with EIA devices using an optional modem cable. The interface is compatible
with Bell 103, 212A, and 202 modems and meets EIA specification RS232-C requirements. The interface conforms to CCITT recommendation V.2.4.
2.2.1 Interface Signals
Table 2-1 summarizes EIA interface signals. The following paragraphs describe interface signals.
2.2.1.1 Protective Ground - This conductor is connected to the LAI20 chassis. It is further connected
to external grounds through the third wire of the power cord.
2.2.1.2 Transmitted Data (TDX) - The direction of TDX is from the LA120. Signals on this circuit
represent serially encoded characters generated by the LA 120.
2.2.1.3 Received Data (RDX) - The direction of RDX is to the LA 120. Signals on this circuit represent serially encoded characters generated by the user's equipment.
Table 2-1

Summary of LA120 EIA Interface Signals

Source

Name

Function

Circuit
CCITT/EIA

I
2
3
4
5
6
7
8
9
10
11*
12t

LAI20
User
LAI20
User
User

TXD
RXD
RTS
CTS
DSR
RLSD

Protective ground
Transmitted data
Received data
Request to send
Clear to send
Data set ready
Signal ground
Carrier detect

101/AA
103/BA
104/BB
105/CA
106/CB
107/CC
102/AB
109/CF

SRTS
SPDI
SRLSD

Sec. req. to send
Speed indicator (FDX)
Sec. carrier det. (HDX)

13
14
15
16
17
18
19*
20
21
22
23*
24
25

User

LAI20
User
User
-

LAI20
LAI20
User
LAI20

SRTS
DTR
RI
SPDS

120/SCA
112/CI
122/SCF
-

Sec. req. to send
Data term. ready
Ring indicator
Speed select (FDX)

120/SCA
108.2/CD
125/CE
111/CH

* Pins 11, 19, and 23 are driven by a common circuit whose function is determined by the
modem and secondary channel SET-UP commands.

t Pin 12 is SPDI for full-duplex operation. For half-duplex operation, pin 12 is SRLSD.

2-8

2.2.1.4 Request To· Send (RTS) - The direction of RTS is from the LA120. The on condition of RTS
means that the LA120 intends to transmit data. After turning this circuit on, the LA120 waits for a
clear to send (transmit enable) condition before starting transmission.
2.2.1.5 Clear To Send (CTS) - The direction of CTS is to the LA120. Although the LA120 physically
receives this signal, it is not used for any purpose. Depending on the modem control protocol in use,
either RLSD, SRLSD, or a timeout after asserting RTS is used to provide a clear to send (transmit
enable) condition.
2.2.1.6 Data Set Ready (DSR) - The direction of DSR is to the LA120. The on condition of DSR
indicates that the user's equipment is capable of transmitting and receiving data signals. The off condition of DSR causes the LA120 to ignore all other interface inputs except ring indicator (RI). In full
duplex without EIA control, this circuit is assumed to always be in the on condition.
2.2.1.7 Signal Ground - This circuit establishes the common ground reference potential for all interface circuits except protective ground. The circuit is permanently connected to the protective ground
circuit.
2.2.1.8 Carrier Detect (RLSD) - The direction of RLSD is to the LA120. The on condition of RLSO
indicates that data transmission from the user's equipment to the LA 120 is enabled. In full duplex
without EIA control, this circuit is assumed to always be in the on condition.
2.2.1.9 Secondary Request To Send (SRTS) - The direction of SRTS is from the LA120. In certain
half-duplex modes, the on condition of SRTS indicates that the LA120 is capable of successfully
processing the received data from the user's equipment. In restraint mode, the off condition of SRTS
indicates that the user's equipment should temporarily suspend the transmission of data. When SRTS
goes on, transmission may be resumed.
2.2.1.10 Speed Indicator (SPDI) (Full Duplex Only) - The direction of SPDI is to the LA 120. The on
condition of SPDI indicates that the baud rate is 1200, regardless of the rate selected by the operator.
The off condition indicates that the operator-selected baud rate is being used.
2.2.1.11 Secondary Carrier Detect (SRLSD) (Half Duplex Only) - The direction of SRLSO is to the
LA 120. The on condition of SRLSD indicates that the user's equipment is capable of successfully
processing the transmitted data from the LA 120.
2.2.1.12 Data Terminal Ready (DTR) - The direction ofDTR is from the LA120. The on condition of
DTR indicates that the LA 120 is capable of transmitting and receiving data signals. The off condition
of DTR may cause the user's equipment to set the DSR (data set ready) to the off condition. When
DTR is off, the LA120 ignores all interface inputs except ring indicator (RI).
2.2.1.13 Ring Indicator (RI) - The direction of RI is to the LA120. If data terminal ready (DTR) is
off, then the on condition of RI causes DTR to turn on. DTR remains on until data set ready (OSR)
turns on or 30 seconds elapses, whichever occurs first. Then DTR turns off. If DTR is on, the on
condition of RI causes a 30-second timeout. If no data is received in 30 seconds, DTR is pulsed low for
233 ms ± 10 percent.
2.2.1.14 Speed Select (SPDS) (Full Duplex Only) - The direction of SPDS is from the LA120. If the
operator-selected bau.d rate is 600 or higher, the LA120 asserts an on condition of SPDS; otherwise,
the LA120 holds this circuit in the off condition.
2.2.2 EIA Interface Cables
BC22A and BC22B interface cables are described in the following paragraphs.

2-9

2.2.2.t BC22A-tO, -25 - BC22A interface cables come in 10 and 25 foot lengths for hookup between
LA120 and computer.* Each end is terminated with a female molded connector. The cable is shielded,
contains six conductors, and is wired in a null modem configuration.
2.2.2.2 BC22B-tO, -25 - BC22B interface cables come in 10 and 25 foot lengths for hookup between
LA 120 and modem. t They can also be used for cable extension. Connectors are molded with a male
connector at one end and a female at the other end. Cable is shielded and has 14 conductors.
2.2.3 Impedance of Terminator
The terminating impedance of the receiving end of the interface circuits has a dc resistance of not less
than 3000 ohms or more than 7000 ohms. When the interface plug is disconnected, interface voltage on
the terminator circuits is -2 V to +2 V.
2.2.4 Rise and Fall Times
The circuitry that receives signals from an interface circuit depends only on signal voltage and conforms to RS232-C rise time and fall time. For control interface circuits, the time required for the signal
to pass through the transition region (-3 V to +3 V) during a change in state does not exceed 1 /lS. For
the transmitted data circuit, the rise time and fall time do not exceed 16.7 /lS through the 6 V range (-3
V to +3 V).
2.2.5 Open Circuit Voltages
The open circuit driver voltage for signal ground on any interface circuit does not exceed -12 V to + 12
V. The terminator on an interface circuit is designed to withstand any input signal within a -25 V to
+25 V range. When the terminating impedance is in the proper range (3000 to 7000 ohms) and the
terminator open circuit voltage is zero, the potential at the point of interface is not less than -5 V to + 5
V or more than -12 V to + 12 V. An open circuit or applied voltage more negative than +0.6 V will be
interpreted the same as a legitimate negative voltage (-3 V to -25 V).
2.3 LAt20 SPECIFICATIONS
The LA120 specifications include data on the printer, keyboard, communications, physical aspects,
and paper. The data in each of these categories is given in Tables 2-2 through 2-6.
Table 2-2

Printer Specifications

Item

Specification

Printing technique

Impact dot matrix, smart bidirectional

Print matrix (width by height)

7X 7

Maximum print speed

180 char/s

Horizontal slew speed

60 in/s

Single line feed time

33 ms

Vertical slew speed

7.5 in/s

*For longer lengths, use BC03M instead of BC22A. Specify desired length.
tFor longer lengths or full 25 connectors, use BC05D instead of BC22B. Specify desired length.

2-10

Table 2-2

Printer Specifications (Cont)

Item

Specification

Paper feed

Pin-feed, tractor drive

Paper type

Fanfold, up to six parts (Table 2-6)

Forms length

1 to 168 lines

Vertical pitch (lines per inch)

2, 3, 4, 6, 8, 12

Horizontal pitch
(characters per inch)
180 char/s
90 char/s

10, 12, 13.2, 16.5
5, 6, 6.6, 8.25

Maximum line length
(varies with horizontal pitch)
5 char/in
6 char/in
6.6 char/in
8 char/in
10 char/in
12 char/in
13.2 char/in
16.5 char/in

66 columns
79 columns
87 columns
108 columns
132 columns
158 columns
174 columns
217 columns

Margins

Left, right, top, bottom

Tabs

217 horizontal, 168 vertical, from keyboard or line

Forms storage

True non-volatile memory (no batteries)

Positioning commands

Horizontal and vertical, absolute and relative

Character set

ASCII upper/lowercase set

National character sets
Standard

United States
Great Britain

Optional

Finland
Sweden
Norway
Denmark
Germany
France

APL character set

Optional

2-11

Table 2-2 . Printer Specifications (Cont)
Item

Specification

Other printer features

• Paper out and cover open interlocks
• Manual and automatic last character view
• Selectable auto new line
• Self-test
• Status message
• Four-digit numeric display used as column counter and to set
parameters,
• Factory stored form setup (10 char/in, 6 lines/in, 66 lines/form;
tab stops every eight columns, etc.)

Table 2-3

Keyboard Specifications

Item

Specification

Keyboard

Typewriter style with multikey rollover

Selectable auto line feed

Standard

Optional num~ric keypad

18 keys including 4 function keys

Feature selecti?n,.

Keyboard entry to non-volatile memory

Other keyboard features

.•
•
•
•

Local form feed key
Local line feed key
Auto repeat on all alphanumeric keys
Selectable keyclick

2-12

Table 2-4

Communications Specifications

Item

Specification

Data transfer

Serial, asynchronous

Baud rates (bits/s)

50, 75, 110, 134, 134.5, 150, 300, 600, 1200, 1800, 2400, 4800, 7200,
9600

Split speeds (bits/s)

• 600 or 1200 receive, with 75 or 150 transmit
• 2400 or 4800 receive, with 300 or 600 transmit

Parity

Odd, even, or none (8th bit mark or space transmitted, or data bits
only)

Input buffer

1024 characters standard
4096 characters optional

Interface

Full EIA standard (includes auto answer/disconnect) 20 rnA optional

Character codes

7-bit ASCII plus ANSI-compatible escape sequences

Modem control protocols
Full Duplex

Selectable XON/XOFF or restraint signal data synchronization

Half Duplex

Coded control with or without reverse channel

Half Duplex

• Reverse channel
• Supervisory
• Line control

Answerback

Up to 30 characters

2-13

Table 2-5

Physical Specifications

Item

Specification

Dimensions
Width
Height
Depth

69.9 cm (27.5 in)
85.1 cm (33.5 in)
61.0 cm (24.0 in)

Weight
Uncrated
Crated

46.4 kg (102 Ib)
63.7 kg (140 lb)

Power
Voltage
Frequency
Input current
Heat dissipation
Printing
Temperature
Operating
Non-operating
Relative Humidity
Operating
Non-operating

87 to 128 V/180 to 256V*
60/50* Hz ± 1 Hz
4.2 A max at 115 V
440 W maximum
10 0 to 40 0 C (50 0 to 104 0 F)
-40 0 to 66 0 C (-40° to 151 0 F)
10 to 90 percent wtih a maximum wet bulb temperature of 28 0 C
(82 0 F) and a minimum dewpoint of 2° C (36 0 F), noncondensing
5 to 95 percent, noncondensing

* With voltage selector switch. See Paragraph 2.1.3, Step 2.

2-14

Table 2-6

Paper Specifications

Item

Specification

General

Continuous, fanfold, pin-feed forms

Width

7.6 to 37.8 cm (3 to 14-7/8 in)

Hole spacing

12.7 mm ± 0.25 mm (0.500 in ± 0.010 in) nonaccumulative over 5 cm (2
in)

Hole diameter

3.81 to 4.06 mm (0.150 to 0.160 in)

Forms thickness
Single part

15 lb paper minimum
0.25 mm (0.010 in) card stock max

Multipart

Up to 6 parts (see Notes)
0.50 mm (0.020 in) max
NOTES

Multipart forms may have only one card part. The card part must be the last part.

Multipart carbonless forms up to six parts may be used. Ribbon must be used on top copy. Firstsurface impact paper is not recommended.

Multipart forms with 3- or 4-prong margin crimps on both margins are recommended. Stapled
forms are not recommended and may damage tractors and other areas of machine. Dot or line
glue margins are acceptable if line is on one margin only. Line glue on both margins prevents air
from escaping and results in poor impressions.

Split forms with each side containing a different thickness or number of sheets are not recommended.

2-15

(

CHAPTER 3
PROGRAMMER'S INFORMATION

3.1 GENERAL
The LA120 uses escape sequences standardized by ANSI (American National Standards Institute) to
control many of its features. For LA120 features lacking an ANSI standard escape sequence, additional escape sequences are defined within the extensions permitted by the ANSI system.
ANSI has established a flexible and comprehensive system for transmitting format and editing information. It can be used with printing terminals like the LA120 and with video terminals and printers
and has the following important advantages.
1.

It is well-defined and well-documented. This greatly decreases the chance of incompatible
implementation and aids in achieving device independence in output.

It has ample provision for future extension without sacrificing compatibility with older programs. The syntax used in ANSI controls allows a large number of new controls to be added
easily.

It is compatible with all frequently used communication protocols. In contrast, many other
systems use control codes that are reserved for communication functions. In these other
systems, codes used for line turnaround, disconnect, and- synchronization get confused with
those used to send parameter values.

Using the escape sequences described in this chapter, the programmer can control the following LA120
features.

•
•
•
•
•
•
•
•
•
•
•

•

Printer character set
Active position
Linefeed-newline mode
Horizontal pitch
Horizontal margins
Horizontal tabs
Vertical pitch
Form length
Vertical margins
Vertical tabs
Product identification
Alternate keypad mode

3-1

3.2

ESCAPE SEQUENCES

3.2.1 Parser Program
An escape sequence is a real-time call to a firmware program that changes an operating parameter of
the LA120 printer. The purpose of the escape sequence is to enable control of the terminal's operating
parameters from a remote computer or terminal. The remote machine sends a string of characters to
the LA 120. Upon being parsed (dissected and interpreted), the character string points to a particular
firmware routine stored in the microprocessor memory. This routine implements the changes to the
printer's operating parameters. Most of the escape sequences deal with forms control (e.g., right and
left margins; top and bottom margins). Other sequences select the character set to be used for printing
or linefeed-newline mode.
The escape sequence is processed by a master software program called the parser. At each level of the
parser program there are choices selected from a look-up table and instructions as to what to do next.
To parse the escape sequence ESC[4e (advance active line by 4), the computer program points to a
table in which the character [ is found. The entry for [ has the choice of pointing to any of seven tables
or of looping in the present table. The logic in the table entries for the [ character knows the next
character is a number; therefore, it points to a table that contains numbers. The entry for [ also gives
an instruction to parse the next character and perform the search in the number table. Finally, after
searching through the tables for the characters [, 4, and e, the pointer points to a terminating routine
that instructs the terminal to advance the active line by four lines and reinitialize the parser program.
3.2.2 Sequence Descriptions
The LA 120 interprets escape sequences sent to it. None of the characters in an escape sequence are
printed. When the end of the sequence is found (or an error occurs), the LA 120 reverts to its normal
printing mode. Control characters (characters with octal codes 000 through 037) may be embedded
anywhere in an escape sequence. The control characters perform their normal function and have no
effect on the escape sequence. If an escape sequence is received by the LA 120 that it does not support,
it is ignored.
An escape sequence that has been only partially processed when the operator enters SET-UP mode will
complete when the operator leaves SET-UP mode. Escape sequences may also be entered and processed while in local mode and may be used in lieu of SET-UP commands.
In the lists of escape sequences that follow, the escape character (octal code 033) is designated as ESC.
Numeric parameters are shown explicitly or designated as n, n}, n2, etc. The graphic characters in
escape sequences are shown using the United States ASCII character set. The characters are spaced
apart for clarity only, the space character (octal code 040) never appears in an escape sequence. The
case of the characters in escape sequences is significant and must be exactly as documented.
A numeric parameter is a sequence of ASCII decimal digits. That is, octal codes 060 through 071. The
parameter is interpreted as an unsigned decimal integer, with the most significant digit transmitted
first. Leading zeros are allowed but are not necessary. A missing parameter is interpreted as a value of
zero. Plus and minus signs are not allowed in parameters.
NOTE
The space character (octal code 040) never appears
in an escape sequence.
Table 3-1 summarizes LA120 escape sequences. Paragraphs 3.2.2.1 through 3.2.2.12 describe these
sequences in more detail.

3-2

Table 3-1

LA120 Escape Sequences

LA120 Feature

Escape
Sequence*

Function/ Comments*

Printer Character Sets

ESC (A

Select character set of Great Britain.

ESC (B

Select character set of United States.

ESC (C

Select character set of Finland.

ESC (E

Select character set of Norway jDenmark.

ESC (H

Select character set of Sweden.

ESC (K

Select character set of Germany.

ESC (R

Select character set of France.

ESC [ n'

Set active column to column n (character after n
is octal code 140)

ESC [ n a

Advance advance column by n columns.

ESC E

Set active column to left margin and increment
active line.

ESC D

Increment active line (active column unchanged).

ESC [ n d

Set active line to line n.

ESC [ n e

Advance active line by n lines.

ESC [ 20 h

Enable linefeed-newline mode.

ESC [ 20 1

Disable Iinefeed-newline mode.

ESC [w
or
ESC [ ow

Set horizontal pitch to 10 char jin.

ESC [ 1 w

Set horizontal pitch to 10 char jin.

ESC [2 w

Set horizontal pitch to 12 char jin.

ESC [ 3 w

Set horizontal pitch to 13.2 char jin.

ESC [4 w

Set horizontal pitch to 16.5 char jin.

ESC [ 5 w

Set horizontal pitch to 5 char jin.

ESC [6 w

Set horizontal pitch to 6 char jin.

ESC [7 w

Set horizontal pitch to 6.6 char jin.

ESC [8 w

Set horizontal pitch to 8.25 char jin.

Active Position

Linefeed-Newline Mode

Horizontal Pitch

3-3

Table 3-1

LA120 Feature
Horizontal Margins

Horizontal Tabs

LA120 Escape Sequences (Cont)

Escape
Sequence·

Function/ Comments·

ESC [ns
or
ESC [n; os

Set left margin to column n.

ESC [; ns
or
ESC [0; ns

Set right margin to column\ n.

ESC [ nl;n2 s

Set left margin to column n I and set right margin
to column n2.

ESC H

Set horizontal tab stop at active column.

ESC 1

Set horizontal tab stop at active column.t

ESC [g
or
ESC 0 g

Clear horizontal tab stop at active column.

ESC [2 g

Clear all horizontal tab stops.

ESC [3 g

Clear all horizontal tab stops.

ESC 2

Clear all horizontal tab stops.t

ESC [n u

Set horizontal tab stop at column n.

ESC [ nl;n2 u

Set horizontal tab stops at column nl and at column n2.
Set horizontal tab stops at columns nl, n2, ... nx

ESC [ nl;n2;
... nx u
Vertical Pitch

(x ~ 16) .

ESC [z
or
ESC [ 0 Z

Set vertical pitch to 6 lines/in.

ESC [ I z

Set vertical pitch to 6 lines/in.

ESC [2 z

Set vertical pitch to 8 lines/in.

ESC [ 3 z

Set vertical pitch to 12 lines/in.

ESC [4 z

Set vertical pitch to 2 lines/in.

ESC [ 5 z

Set vertical pitch to 3 lines/in.

ESC [ 6 z

Set vertical pitch to 4 lines/in.

3-4

Table 3-1

LA120 Escape Sequences (Cont)

LA120 Feature

Escape
Sequence·

Form Length

ESC [ n t

Set form length to n lines.
Set top margin to line I.
Set bottom margin to line n.
Set active line to line I.

Vertical Margins

ESC [ n r
ESC [ ; n r
ESC [ nl;n2 r

Set top margin to line n.
Set bottom margin to line n.
Set top margin to line nl and
set bottom margin to line n2.

Vertical Tabs

ESC J

Set vertical tab stop at active line.

ESC 3

Set vertical tab stop at active line. t

ESC [ I g

Clear vertical tab stop at active line.

ESC [4 g

Clear all vertical tab stops.

ESC 4

Clear all vertical tab stops. t

ESC [n v

Set vertical tab stop at line n.

ESC [ nl;n2 v

Set vertical tab stops at line n 1 and at line n2.

ESC[ nl;n2;
... nxv

Set vertical tab stops at lines n J, n2, ... nx(x ~
16) .

Product Identification

ESC [C
or
ESC [ 0 c

LA 120 transmits ESC [ ? 2 c

Alternate Keypad Mode

ESC =
ESC>

Enable alternate keypad mode.
Disable alternate keypad mode.

Function/ Comments·

* n represents a numeric parameter.

t This escape sequence is available for compatability with the LA36.
3.2.2.1

Printer Character Sets

United States and British Character Sets -

The LA120 is capable of receiving and printing both the
United States ASCII character set and the British version in which the character H#" is replaced by the
character "£". The United States ASCII character set is shown in Table 3-2. Refer to Table 3-1 for the
escape sequences that select the printer character sets of the United States and Great Britain.

3-5

Table 3-2

United States ASCII Character Set

Code

Char

Code

Char

Code

040
041
042
043
044
045
046
047
050
051
052
053
054
055
056
057
060
061
062
063
064
065
066
067
070
071
072
073
074
075
076
077

space
!

100
101
102
103
104
105
106
107
110
111
112
113
114
115
116
117
120
121
122
123
124
125
126
127
130
131
132
133
134
135
136
137

140
141
142
142
144
145
146
147
150
151
152
153
154
155
156
157
160
161
162
163
164
165
166
167
170
171
172
173
174
175
176

,&
(
)

*
+

,
-

0
1
2
3
4
5
6
7
8
9

<
=

A
B

C
D
E
F
G
H
I
J
K
L
M
N

0
P

Q
R
S
T
U
V

W
X

Y
Z
[

\
]
A

Char

,
a
b
c
d
e
f
g
h
1

J
k

I
m
n
0

P
q
r
s
t
u
v
w
x
Y
z
{

}
'"

Optional Character Sets - Five additional national character sets and an APL character set are available as an option. The national character sets are selected by the operator, using SET-UP commands,
or by the programmer using escape sequences. The national character sets differ from United States
ASCII in only a limited number of code positions.
The code differences among the national character sets are shown in Table 3-3. Refer to Table 3-1 for
the escape sequences that select the optional printer character sets.
3.2.2.2 Active Position - Active position may be either active column or active line. Active column is
defined as the column where the next character will normally be printed. Active line is defined as the
line where the next character will normally be printed. Column and line numbers begin with one, not
zero. Printable characters normally increment active column. Line feeds normally increment active
line. Active column and active line are collectively known as active position.

3-6

Table 3-3

Code Differences Among National Character Sets
Code
135 136 140

Character Set

043

100

133

134

United States

[

]

Great Britain

[

]

Finland
Sweden
Norway /Denmark
Germany
France

:J;

A
A

• a
§

175

176

{

}

{

}

173

174

e
e

Active position is only loosely linked to the physical position of the LA120 print head and paper
mechanism. In general, active column is only recorded when a character is actually printed. Any
previous history of active column values is not significant. Active line is different because it may only
be advanced, since backward paper motion is not allowed. When the LA 120 is idle, active and physical
positions are identical.
In the LA120, bell characters have only an active line attribute. They are not guaranteed to be sounded
at any particular column within a line.
In addition to the normal position control characters (space, backspace, carriage return, line feed,
horizontal tab, vertical tab, and form feed), active position escape sequences listed in Table 3-1 also
modify active position.
3.2.2.3 Linefeed-Newline Mode - Linefeed-newline mode is controllable both by the operator and the
programmer. If linefeed-newline mode is enabled, the characters line feed, vertical tab, and form feed
each return the active column to the left margin in addition to their normal functions. Linefeednewline mode may be enabled by the operator selecting choice 2 (line feed) in the printer new line
character SET-UP command. The mode is disabled any time the operator selects choice 1 (none) or
choice 3 (carriage return) in the printer new line character SET-UP command.
Table 3-1 contains the escape sequences that control linefeed-newline mode.
3.2.2.4 Horizontal Pitch - Horizontal pitch determines the width of printed characters as well as their
spacing. The LA120 has eight different horizontal pitches. Any combination of pitches may be used on
a single print line. Changing horizontal pitch modifies the active column. The resulting new active
column is that of the first column boundary at or to the right of the physical position of the previous
active column in the old pitch. It is calculated as:
- 1 + (Oldcol-l )*Oldpitch
N ewco I 1 Newpitch

where: Newcol
= new active column
Newpitch = new pitch in chars/in
Oldcol
= old active column
Oldpitch = old pitch in chars/in

3-7

The division performed above is integer division. Any remainder or fractional part of the quotient is
discarded.
The escape sequences that set horizontal pitch are listed in Table 3-1.
3.2.2.5 Horizontal Margins - Printing is permitted only within the inclusive left and right margins. A
carriage return character sets the active column to the left margin. Attempting to move the active
column left of the left margin sets the active column equal to the left margin. Attempting to move the
active column more than one column right of the right margin executes an auto newline if auto newline
is enabled. If auto newline is disabled, an error bell sounds and the character or command that attempted the motion is discarded.
Horizontal margins may be set so long as the following is true.
1 ~ left margin ~ right margin ~ max column
Note that maximum column is a function of horizontal pitch.
maximum column = 13.2 inches * horizontal pitch
where the product is rounded down to the nearest column.
The horizontal margin escape sequences listed in Table 3-1 set the left and right horizontal margins.
3.2.2.6 Horizontal Tabs - The LA120 has 217 possible horizontal tab stops, one for each column. Tab
stops are associated with column numbers, not physical positions on the paper. Thus, changing horizontal pitch will also change the physical position of tab stops. Each stop may· be set or cleared
independently. Setting a stop already set has no effect; the same is true for clearing a stop already
cleared. Tab stops may be set or cleared without regard to margins or horizontal pitch.
The horizontal tab escape sequences used to set and clear horizontal tab stops are listed in Table 3-1.
3.2.2.7 Vertical Pitch - Vertical pitch determines the spacing between lines, not the height of printed
characters. Changing vertical pitch does not affect active line number; but it does clear vertical margins. The escape sequences that set vertical pitch are listed in Table 3-1.
3.2.2.8 Form Length - Form length is defined in lines, not physical units. Therefore, changing vertical
pitch will alter the physical form length. Forms may be from 1 to 168 lines in length. Changing form
length clears vertical margins and defines the current line as line one. The escape sequence that sets
form length is listed in Table 3-1.
3.2.2.9 Vertical Margins - Printing is permitted only on lines within the inclusive top and bottom
margins. When vertical pitch or form length are changed, these margins are cleared; that is, the top
margin is set to line one and the bottom margin is set to the form length. The following must be true to
successfully set new vertical margins.
1 ~ top margin ~ bottom margin ~ form length
Whenever active line < top margin or active line > bottom margin, the active line is set to the top
margin. For example, a line feed performed at the bottom margin will execute a form feed.
The escape sequences that set the top and bottom margins are listed in Table 3-1.

3-8

(
\

3.2.2.10 Vertical Tabs - The LA120 has 168 vertical tab stops set and cleared similar to horizontal
tab stops. Vertical tab stops are associated with specific line numbers, not physical positions on the
paper. Thus, changing vertical pitch changes the printing position of vertical tabs.
The escape sequences that set or clear vertical tab stops are listed in Table 3-1.
3.2.2.11 Product Identification - The LA120 terminal automatically transmits an answer to the ANSI
standard request for a device attributes escape sequence.
The escape sequence that causes the LA120 to transmit its product identification escape sequence is
listed in Table 3-1.
3.2.2.12 Alternate Keypad Mode - Alternate keypad nl0de allows application programs to differentiate between keystrokes performed on the optional numeric pad and those performed on the main
keyboard so that the numeric pad may be used for commands or special functions.
Alternate keypad mode is controllable by the operator using the alternate keypad mode SET-UP
command, or by the programmer. If alternate keypad mode is disabled, the keys on the optional
numeric keypad transmit the codes that correspond to the keycap legends. If alternate keypad mode is
enabled, each of these keys transmits the escape sequence specified in Table 3-4.

Table 3-4

Escape Sequences Transmitted in Alternate Keypad Mode

Code Transmitted
Alternate
Keypad Mode

Key

Normally

PFI
PF2
PF3
PF4
ENTER

ESCOP
ESCOQ
ESCOR
ESCOS
Same
as RETURN key
,

o(number)

1
2
3
4
5
6
7
8
9

ESCOP
ESCOQ
ESCOR
ESCOS
ESCOM
ESCOI
ESCOm
ESCOn
ESCOp
ESCOq
ESCOr
ESCOs
ESCOt
ESCOu
ESCOv
ESCOw
ESCOx
ESCOy

The escape sequences that control alternate keypad mode are listed in Table 3-1.

3-9

3.3 CONTROL CHARACTERS
The LA120 receives the control characters listed in Table 3-5 and responds accordingly.

Table 3-5

LA120 Control Characters

Code

Mnemonic

Name

000
003
004
005
007
010
011
012
013
014
015
016
017
020
030
032
033
177

NUL
ETX
EOT
ENQ
BEL
BS
HT
LF
VT
FF
CR
SO
SI
DLE
CAN
SUB
ESC
DEL

Null
End of Text
End of Transmission
Enquiry
Bell
Backspace
Horizontal Tabulation
Line Feed
Vertical Tabulation
Form Feed
Carriage Return
Shift Out
Shift In
Data Link Escape
Cancel
Substitute
Escape
Delete

Control characters not listed in Table 3-5 are always ignored when received by the LA120. Paragraphs
3.3.1 through 3.3.17 describe each character.
3.3.1 Null or Delete (NUL or DEL)
Null and delete characters cause no operation. But they are different from ignored characters in that
they are disposed of without occupying space in the input buffer. Thus, they are fill characters and
truly equivalent to idle marking time.
3.3.2 End of Text (ETX)
If the LA 120 is operating in half duplex with ETX turnaround, the end of text character is recognized
as the turnaround character. If the LA120 is operating in any other full- or half- duplex mode, the ETX
character has no effect.
3.3.3 End of Transmission (EOT)
If the LAI20 is operating in half duplex with EOT turnaround, the end of transmission character is
recognized as the turnaround character. If the LA 120 is operating in any other full- or half- duplex
mode, the EOT character is recognized as a disconnect request, unless the auto disconnect feature is
turned off. For disconnect request in half duplex with EOT turnaround, see Data Link Escape (DLE)
(Paragraph 3.3.14).
3.3.4 Enquiry (ENQ)
The LA120 automatically transmits its answerback message upon receipt of ENQ.

3-10

3.3.5 Bell (BEL)
The bell character sounds a momentary 2400 Hz tone. No more than eight bells can be pending at any
one time.
3.3.6 Backspace .(BS)
The backspace character decrements the active column, unless the active column is at the left margin,
in which case the backspace character is ignored.
3.3.7 Horizontal Tab (HT)
The horizontal tab character advances the active column to the next horizontal tab stop greater than
the current active column, but no greater than the right margin. If there is no such tab stop, the active
column is advanced to the column after the right margin.
3.3.8 Line Feed (LF)
The line feed character increments the active line, unless the active line is at the bottom margin, in
which case it sets the active line to the top margin of the next page. If linefeed-newline mode is enabled,
the active column is set to the left margin.
3.3.9 Vertical Tab (VT)
The vertical tab character advances the active line to the next vertical tab stop greater than the current
active line but no greater than the bottom margin. If there is no such tab stop, the active line is set to
the top margin (on the next page). If linefeed-newline mode is enabled, the active column is set to the
left margin.
3.3.10 Form Feed (FF)
The form feed character advances the active line to the top margin of the next page which mayor may
not be the physical top of the form. If linefeed-newline mode is enabled, the active column is set to the
left margin.
3.3.11 Carriage Return (CR)
The carriage return character returns the active column to the left margin. If carriage return is selected
as the printer new line character, the active line is incremented.
3.3.12 Shift In (SI)
The shift in character shifts the printer to the primary character set. If no secondary character set (such
as APL) is installed, this character has no effect.
3.3.13 Shift Out (SO)
The shift out character shifts the printer to the secondary character set. If no secondary character set
(such as APL) is installed, or if alternate character set is disabled, this character has no effect.
3.3.14 Data Link Escape (DLE)
If the LAl20 is operating in half duplex with EOT turnaround, the data link escape character, when
received or transmitted immediately prior to an EOT, causes the EOT to be interpreted as a disconnect
request. If the LAl20 is operating in any other full- or half-duplex mode, the DLE character has no
effect.
3.3.15 Cancel (CAN)
The cancel character terminates any pending escape sequence and causes the sequence to be ignored.
3.3.16 Substitute (SUB)
The substitute character is interpreted as being in place of a character received in error. Characters
received with parity errors are converted to the SUB character. If characters are ever lost due to input

3-11

buffer overflow, a SUB character is placed in the input buffer at that point. The SUB character is
printed as the following graphic symbol:

The SUB character also has the effect of a cancel character.
3.3.17 Escape (ESC)
The escape character is interpreted as introducing an escape sequence. Escape sequences are described
in detail in Paragraph 3.2.
3.4APL CHARACTER SET
If the alternate character set SET-UP feature is enabled, the optional APL character set can be selected
by the SO control character, independent of the national. character set in use. The SI control character
returns the printer to the previously selected national character set.
For the APL keyboard to work properly, the keyboard character set must have been set by the operator to United States or Great Britain. The APL character set is shown in Table 3-6.
Table 3-6

APL Character Set

Code

Char

Code

Char

Code

040
041
042
043
044
045
046
047
050
051
052
053
054
055
056
057
060
061
062
063
064
065
066
067
070
071
072
073
074
075
076
077

space

100
101
102
103
104
105
106
107
110
111
112
113
114
115
116
117
120
121
122
123
124
125
126
127
130
131
132
133
134
135
136
137

140
141
142
143
144
145
146
147
150
151
152
153
154
155
156
157
160
161
162
163
164
165
166
167
170
171
172
173
174
175
176

"
)

]
V
/\
~

0
1
2
3
4
5
6
7
8
9
(
[

,
X

a
J.

n
L
€

-'9
tJ.

\
0

0
I
T

e
~

'?
f

r
H

'u"
w
;:)

t
c
f-

I-i

3-12

Char
A
B
C
D
E
F
G
H
I
J

K
L
M
N

0
P

Q
R
S
T
U
V
W
X

Y
Z
{
-t

}
$

3.5 SAMPLE FORM SETUP USING ESCAPE SEQUENCES
All form control features available to the operator in SET-UP mode can also be transmitted to the
LA120 using escape sequences. The sample form illustrated in Figure 3-1 could be set up using the
escape sequences in Table 3-7.

Table 3-7 Escape Sequences for Sample Form
Escape Sequence

Function/ Comments

ESC [ 1 z

Selects 6 lines/in.

ESC [66 t

Sets form length to 66 lines and sets top-of-form at current line.

ESC [4; 5 8 r

Sets top margin at line 4 and bottom margin at line 58.

ESC [4 g

Clears all vertical tabs.

ESC [ 8; 2 0; 2 5; 4 5 v

Sets vertical tabs at lines 8, 20, 25, and 45.

ESC [1 w

Sets horizontal pitch to 10 char/in.

ESC [3; 8 2 s

Sets left margin to column 3 and right margin to column 82.

ESC [2 g

Clears all horizontal tabs.

ESC [ 1 0; 2 1; 4 1 u

Sets horizontal tabs at columns 10,21, and 41.

3.6 SYNCHRONIZATION
When the LA120 receives a character (other than the fill characters, NUL and DEL), it stores it in its
1000 character input buffer. When the printer is ready, characters are fetched from the input buffer
and printed. If the printer falls behind by more than about 1000 characters, the input buffer overflows
and data is lost. There are three ways to avoid buffer overflows.
1.

Send data only as fast as it can be printed. When receiving data at 1200 baud or less, the
LA120 can keep up with normal character sequences. Very short lines and multiple form
feeds cannot be printed this fast. Fill characters may be used to slow the effective data
transmission speed in these cases. Fill time formulas are given in Paragraph 3.6.2.

Limit the length of your message to the LA120's input buffer size. If the buffer is empty at
the beginning of your transmission, you can send a message of about 1000 characters without worrying about buffer overflow.

Use a terminal synchronization protocol, such as XON/XOFF or restraint mode. Using a
synchronization protocol, the LA120 can tell the 'data source when to pause in sending data
and when to resume. Synchronization allows maximum throughput and eliminates the need
for fill character calculations and message size limits.

3-13

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Figure 3-1

Sample Form SET-UP

3-14

When synchronization is used, the LA120 constantly monitors the number of characters stored in its
input buffer. When the number of characters exceeds a "high water mark," the LA120 signals the data
source to pause temporarily. Meanwhile, the printer continues to take characters out of the input
buffer. When the number of characters remaining is less than a "low water mark," the LAI20 signals
that transmission may resume. The values used for the high and low water marks are selected by the
. buffer control SET-UP command.
The LA120 also sends a pause signal when the printer is not ready due to error conditions or operator
actions. Running out of paper or detecting a print head jam can cause a pause request to be sent. The
operator can induce a pause request by opening the cover or entering SET-UP mode.
The pause and resume signals to the data source are sent in either or both of two ways:
1.

Using the control characters XON (octal code 021) and XOFF (octal code 023),

U sing the EIA signal SRTS in restraint mode.

Restraint mode operation is suited for local, hard-wired installations, especially when the LA120 is
used as a serial line printer replacement. Restraint mode is selected using SET-UP commands: "S"
(secondary channel) must be "1" (enabled) and "M" (modern/protocol) must be "1" (full duplex, no
EIA controls).
XQN/XOFF is suitable for either local or remote operation so long as the connection is full duplex.
To select XON/XOFF operation, the "X" set-up must be set to "1" (enabled). The XON/XOFF
protocol is complicated by the fact that the synchronization characters may be interspersed between
the characters typed at the LAI20 keyboard. The operator can tell the data source to pause by typing
XOFF (CTRL-S) and to resume by typing XON (CTRL-Q). To make sure that neither the buffer
controller's nor the operator's pause requests are lost, typed characters may be transmitted with an
XOFF character immediately following.
IfXON/XOFF is enabled, the LAI20 will transmit XON when first powered up and transmit enabled.
3.6.1 Synchronization Limits
Synchronization limits are given in Table 3-8.
Table 3-8 Synchronization Limits

"B" SET-UP
Choice

Low Limit

High Limit

o(small)

50 char
256 char

60 char
576 char

1 (large)
3.6.2

Fill Time Formulas

3.6.2.1 Horizontal Movement - Includes horizontal tabs and horizontal positioning escape sequences.
First, convert to actual number of columns moved, then allow 15 ms for each of the first ten columns
(30 ms in double-width pitches) and 5.5 ms for each additional column (11 ms in double-width
pitches).
3.6.2.2 Vertical Movement - Includes line feeds, vertical tabs, form feeds, and vertical positioning
escape sequences. First, convert to actual number of lines moved, then allow 33 ms for the first line
moved up to 1/6 inch and 135 ms for each additional inch.
3-15

3.7 KEYBOARD OPERATION
The LA120 operator's console contains a typewriter-style keyboard resembling an office typewriter in
key size, shape, and location. The keyboard also contains a 4-digit numeric display and eight binary
indicators. There is provision for an optional, field installable numeric keypad.
The operator uses the keyboard to transmit codes. If the LA120 is transmit-enabled, codes are transmitted as each key is pressed except during auto repeat activity or with certain combinations of three
or more keys held down which cannot occur in normal touch typing. If the LA 120 is not transmitenabled, keystrokes are stored in a 16-character buffer for future transmission. If more than 12 keystrokes are in the buffer, each keystroke generates a 400 Hz tone to indicate that the buffer is full or
nearly full. The buffer will be cleared without transmission any time SET-UP mode is entered or
exited, line/local status is toggled, or a break is transmitted.
3.7.1 Auto Repeat
If auto repeat is enabled and a key that generates the space, backspace, or delete code or any printable
character code is held down for more than 0.6 second, the code for that key is transmitted repeatedly at
7.5 char/sec per second, gradually increasing to 25 char/sec, or at a rate determined by the baud rate,
whichever is slower. If auto repeat is in process, all keystrokes are ignored until the repeating key is
released. If more than one key is held down prior to the start of auto repeat, only the last key pressed is
subject to auto repeat.
3.7.2 Printable Character Keys
There are 47 keys that generate printable character codes. The relationship between these keys and the
SHIFT and CAPS LOCK keys is such that each of the 26 alphabetic keys transmits the lowercase code
unless either or both of-the SHIFT keys are down, or unless the CAPS LOCK key is down. Each
nonalphabetic key generates two different codes. One code is generated if neither SHIFT key is down.
The other code is generated if either or both of the SHIFT keys are down. Unlike the SHIFT LOCK
key of a typewriter, the CAPS LOCK key does not affect the nonalphabetic keys. The codes generated
by each code generating key are shown in Figure 3-2.

Unshifted Codes Shown Below legends)

033
ESC D:I]41
1I
033
061
011
TAB
011

DODD
46 1 IrnJ [!]1
D:{]
D

Octal Codes Generated by Keyboard
(Shifted Codes Shown Above Legends;

~oo
05~
2 @ [ID43
3 # [ID44
4 $ [!1J45
5 % GZJ36
6"
7&
8
062

063

064

065

066

067

070

071

a:kJ51
0)
060

~531~76
+ \ -

BACK
SPACE

055

075

010

140

CtJ21
[l]27
DJ22
[!]31
[!]25
ChJ11
OJ17
[!]20
C[]73
Q
W [!J05
E
R [!]24
T
Y
U
I
0
P
[ I []J75
JI
161
167
145
162
164
171
165
151
157
160
133
135

177

llll~l 111;3111~ 111~6111g71~f1Ylf1;plf1Iil1
L.lliJlJgjlJ.EJl!i!J ~7211 ~4.~ I R~~N
D~
141

163

144

146

147

073

047

015

.
111~ 111~6111g21~ll~511 ~~411 O~ I ~7: ID
Dr-I----..lll~2111~O
.

172

170

143

166

142

155

054

056

Figure 3-2 Octal Codes Generated by Keyboard

3-16

057

MA3388

(

3.7.3 Control Character Keys
!here are seven keys that generate control character codes. The codes generated by these keys are
mdependent of the SHIFT and CAPS LOCK keys. The control character keys and their functions are
listed in Table 3-9.
In coded control half duplex, the RETURN key transmits the turnaround character automatically
after transmitting its normal code or codes.

Table 3-9

Control Character Keys

Key

Octal Code

Function

RETURN
LINE FEED
BACKSPACE
TAB
Space Bar
DELETE
ESC

015 or 015012
012
010
011
040
177
033

CR orNL
LForNL
BS
HT
SP
DEL
ESC

3.7.4 CTRL (Control) Key
The CTRL key is used in conjunction with certain other keys on the keyboard to generate control
character codes. The CTRL key is also used in conjunction with the SET-UP key to enter SET-UP
mode.
The codes generated and keys affected by the CTRL key are independent of SHIFT and CAPS LOCK
keys. It is never necessary to hold both the CTRL key and the SHIFT key down in combination with
another key to generate control character codes. Also, there is only one CTRL key combination for
each of the 32 control characters. Because of these requirements, there are three control characters
whose locations on the LA120 may differ from other terminals. These characters and their locations on
the LA120 and other terminals are shown in Table 3-10.
Table 3-10
Code

Variations in Control Character Locations

LA120

NUL
(000)

CTRL

Other Terminals

-I Space Bar I

RS
(036)

CTRL-I, I

CTRL-SHIFT -\ ~

IT]

CTRL-SHIFT -1-=-1

US
(037)

CTRL-SHI FT -\

CTRL-

3-17

The characters and codes generated by each key when the CTRL key is held down are shown in Figure
3-3.
Characters Generated by Keyboard
with CTRL Key Held Down

DODD

(Mnemonics Shown Above Legends;
Octal Codes Shown Below Legends)

!!~ GBBBBBGBGBEJI =+ I~ ~b\\~ D
I T~TB I XgN I I E~Q II D~211 D~ IfEfll
l...2llJ N~K Iffflmi
l2iJLm1J D~E I Iryl
~
L
S~H r~FFII E~T II A;K I
IfBJl
~mD': D.. R~~RN
~
Li12J LF~NL Lil.!Juu.J
Or--ll
E1B

011

021

027

Elsie

006

022

024

026

020

033

001

023

004

006

007

012

015

D,. .I. . .; . . ;. ,-. . .;. . . . ;. . . .I~[%][ZJ[ZJ[Z][!][!][JDrnJD
I
:
I

MA3387

Figure 3-3 Characters Generated by Keyboard with
CTRL Key Held Down

3.7.5 Optional Auxiliary Keypad
The optional auxiliary keypad contains 18 keys that transmit the codes for the characters or escape
sequences specified in the escape sequences section of this chapter (Paragraph 3.2).
3.7.6 BREAK Key
Pressing the BREAK key causes the LA120 to transmit a short break signal of 233 ms duration.
Holding one or both SHIFT keys down and pressing the BREAK key causes the LA120 to transmit a
long break disconnect signal of 3.5 seconds duration.
The interface leads involved in transmitting break signals are described in Chapter 4 of the LA 120 User
Guide.
3.7.7 VIEW Key
If automatic view is in use and the printer has been idle but has not yet timed out the automatic view
delay time, pressing the VIEW key causes the view operation to be performed.
If automatic view is not in use, pressing and holding the VIEW key causes the print head to idle at the
viewing position. With the VIEW key released, the print head idles at the ready to print position.
Where there is no character to print, the carriage moves to the print cell immediately to the left of the
cell designated by the active position (ready to print position). If the printer remains idle longer than
the automatic view delay time, the carriage moves to the right to facilitate viewing of the last character
printed (viewing position).
The automatic view delay time is a function of keyboard activity. If characters are being typed at a
touch typing rate or faster, the time is set long enough to pr~vent erratic carriage motion. Otherwise, it
is set to provide instant visibility of single typed or received characters. The automatic view operation
may be disabled by the operator using a SET-UP command (SET-UP Z).

3-18

CHAPTER 4
LA120 THEORY OF OPERATION

4.1 BASIC SYSTEM CONFIGURATION
A block diagram of the LAI20 is shown in Figure 4-1. The LAI20 is a microprocessor-controlled
system that utilizes the interaction of firmware programs with hardware circuits to perform control
functions and provide functional characteristics.
As shown in Figure 4-1, the microprocessor, memory, and peripheral devices communicate via a
common data bus. Peripheral devices in the LA 120 include the following major functional items:
I.

A single chip LSI printer controller that provides an interface to all functional elements of
the printer,

A serially accessed non-volatile memory that stores set-up data when machine is turned off,

A keyboard consisting of an array of switches and a number of LED displays, and

A serial transmitter and receiver that provides data communication interface.

4.1.1 Microprocessor
The LAI20 firmware is executed by an 8080A 8-bit microprocessor running from a 2 MHz clock.
Although the microprocessor has a 16-bit address space, typically only part of the address is decoded
by many devices on the bus. The microprocessor receives interrupt requests and RST vectors from the
DC305 printer controller. When powering up, the microprocessor's reset line is asserted, thus starting
program execution from location 0 with interrupts disabled.
4.1.2 Device Addressing
Both memory and I/O addressing are used in the LA120. In many cases, address lines are used to
output data to devices as well as to select them. Conversely, data bits are used in some cases to select
parts of a device.

4-1

000
PRINTER CONTROLLER
-DC30S-

MICROPROCESSOR
AND MEMORY
uP

{8080A

DOT DATA

8224
8228

HORIZONTAL PITCH

RAM-2114

ROM-8316E

::>

SPEED COMMAND

NON-VOLATI LE
MEMORY
-ER1400-

I
4

«
t. .1 ~

PRINT
HEAD AMPL
-1......- - - - - - - -...

CARRIAGE
POSITION
COUNT

POSITION

- - --

DOT
PRINT
CONTROL

DOT INTERRUPT

- - --

CARRIAGE
SPEED
CONTROL

CARRIAGE
MOTOR AMPL

LlNEFEED
CONTROL

LlNEFEED
AMPL

LF INTERRUPT
LlNEFEED STEP

POSITION
ENCODER

RIBBON

PAPER

STEPPER
MOTOR
TRACTOR FEED

KEYBOARD
ARRAY

~I BELL CONTROL

BELL COMMAND

BELL
AMPL

2.S MS INTERRUPT
SERIAL
RECEIVER
AND
TRANSMITTER

EIA

+24V
TO POWER CI RCUITS
-

BAUD RATE SELECT

SPEAKER

FREQUENCY
GENERATION
BAUD RATE CLOCKS

+5V
+12V
TO
LOGIC
CIRCUITS

POWER
SUPPLY

ACINPUT

INTERFACE
MA-4707

Figure 4-1

LA 120 Block Diagram

4.1.2.1

Memory Space - LAI20 memory read/write decoding is summarized in Table 4-1.

Table 4-1

LA120 Memory Read/Write Decoding

Address Range*

Device

OOOOH - OFFFH
IOOOH - I FFFH
2000H - 2FFFH
3000H - 3FFFH
4000H - 4FFFH
5000H - 5FFFH
6000H - 6FFFH
7000H - 7FFFH
8000H- FFFH

ROM
ROM
ROM
Keyboard (read)/Display (write)
RAM
RAM
N on-volatile memory
DC305 printer controller
Not used - reserved for options

*The "H" suffix indicates hexadecimal notation.

4.1.2.2

I/O Space - LAI20 I/O space is used as shown in Table 4-2.

Table 4-2

I/O Space Allocation

I/O Address
(Binary)*

Device

OxxxxxOx
Oxxx xxix
Ixxx xxxx

8251A USART
Utility I/0 Ports
Not used - reserved for options

*x = Don't care.

4.1.3 Interrupts
The LAI20 receives interrupts from the DC305 printer controller and the 8251A USART. The DC305
will present one of four interrupt vectors to the microprocessor, depending on the source of the interrupt request(s). These are shown in Table 4-3.

4-3

Table 4-3

Interrupt Vectors

Source of Interrupt Request Request
Interrupt
Vector

DC305
Dot/Timer

8251A
USARTRxRdy

DC305
2.5ms
Clock Tick

RST3
RST7
RST3
RST5
RST 1
RST3
RST 1

F
F
F
T
T
T
T

F
T
T
F
F
T
T

T
F
T
F
T
F
T

As Table 4-3 indicates, the USART receiver ready interrupt is masked by either or both of the other
interrupt sources.

4.1.4 ROM
The standard LA120 has five 16K bit ROMs in sockets. They occupy addresses 0000H-07FFH,
0800H-OFFFH, ... , 2000H-27FFH, respectively. The European/ APL options require additiona1
ROM from 2800H-2FFFH. The ROM sockets actually decode only address bits AI2-AI5; All is a
chip select on the 16K ROM chip. The conventional ROM placement is shown in Figure 4-2a.
The European/APL option ROM is a 64K bit device (of which only 32K is used) replacing ROM 4 in
the rightmost socket. When 64K bit ROMs are phased in for the standard LA 120, the socket now used
for ROM 0 will be addressed by OOOH-IFFFH and ROM placement will be as shown in Figure 4-2b.

SOCKET ADDRESS:

1800H
THRU
1FFFH

1000H
THRU
17FFH

1XXXH

0800H
THRU
OFFFH

OOOOH
THRU
07FFH

2000H
THRU
27FFH

OXXXH

2XXXH

a. 16K Bit ROMs

0
(NOT
USED)

(NOT
USED)

OOOOH
THRU
1FFFH

2000H
THRU
2FFFH

b. 64K Bit ROMs
MA-4703

Figure 4-2

ROM Placement

4-4

4.1.5 RAM
The standard LAl20 has 2K bytes of RAM. This RAM is logically in two parts, one addressable from
4000H-4FFFH and the other from SOOOH-SFFFH. RAM addresses are not fully decoded, so that
each IK portion of the RAM has "ghosts" at IK intervals in its address range. To be exact, address
bits All and AIO are not significant. Thus, locations 4000H, 4400H, 4800H, and 4COOH are identical.
By convention, LAl20 firmware defines RAM to be the contiguous 2K space from 4COOH-S3FFH. At
no time does the firmware rely on the ghosting effect, nor is it tested by RAM diagnostics. The RAM
address map is shown in Figure 4-3.

-----4000H----(GHOST)

-----4400H----(GHOST)

-----4800H----(GHOST)

-----4COOH----LOW 1K OF RAM

-----5000H----HIGH 1K OF RAM

-----5400H----(GHOST)

-----5800H----(GHOST)

-----5COOH----(GHOST)

-----6000H----MA·4704

Figure 4-3

RAM Address Map

4.1.6 Keyboard
In the LA120, the microprocessor directly reads the keyboard switch array, filters the data, and generates the proper codes or other actions in firmware, thereby giving the programmer complete freedom
in specifying keyboard functionality.
4.1.6.1 Keyboard Addressing (Table 4-4) - The keyboard switch array is read using memory-mapped
I/0. All reads in the address range 3000H-3FFFH will select the keyboard switch array.
Keyboard addresses are only partially decoded: in particular, address bits AS-All are ignored. The
keyboard switch array appears to the microprocessor as 16 bytes of bit-encoded data - one bit per
switch. Switches are grouped into two banks: the first bank is selected by A3, the second by A4. If both
are selected, the microprocessor will read the logical OR of the two. By convention, LAl20·firmware
uses addresses 3008H-3017H to access the keyboard which relates, in hardware, to a direction of scan
from BREAK toward ESCAPE. The direction was originally arbitrary but is now crucial to proper
operation of the receive only control panel in the LAI20-RA.
Bits that read as O's are open, undepressed keys, while 1's are keys that are closed. In both banks,
data bits DO-D4 contain the state of regularly decoded switches; bits DS and D6 are constant 1'so In
the first bank only, bit D7 contains data for separately decoded switches; in the second bank, D7
is always O.

4-S

Table 4-4

Keyboard Addressing

Data Bit
D4

DO·

BREAK

LOCAL
LF

no
key

PF4

DEL

LOCAL
FF

PF3

no
key

HERE
IS

PF2

SHIFT

LINE
LOCAL

PFI

300C

CAPS
LOCK

N-

300D

CTRL

300E

RET

300F

SET-UP

3010

(unused)

3011

3012

3013

3014

3015

3016

3017

Address
DS

3008

space
bar

(unused)

3009

cover

300A

paper

300B

opt

=
{
[

)

(

NO
N9

ESC

TAB

VIEW

flag

•

&
A

%
$

2
!

. • Nx = key labeled "X" on numeric pad.

4-6

ENTER

4.1.6.2 Switch Matrix - All of the keys in datu bits DO-D4 are part of a single two-dimensional
switch matrix. As a result of the keyboard's design, simultaneous pressing of three or more keys can
make it appear that one or more additional keys are also pressed but in fact are not. These false keydown indications are detected by LAI20 firmware, and prevented from generating any codes.
4.1.6.3 Separately Decoded Keys - Certain inputs from the keyboard must always be readable: these
have been separately decoded and thus their data is always valid. These inputs are all in the first bank
of switches, in data bit D7. The eight separately decoded keys are the space bar, cover interlock, paper
out sensor, SHIFT key, CAPS LOCK key, CTRL key, RETURN key, and SET-UP key. The cover
interlock will read 0 if open, 1 if closed; the paper out sensor is 0 if paper is out, 1 if paper is present.
4.1.7 Display
The LAI20 has a 4-digit seven-segment LED display and eight individual LEDs above the keyboard
array. Writes to addresses 3000H-3FFFH will access the display. Address bits A5-All are "don't
cares." All data bits are "don't cares." In the LAI20 firmware, address bits A8-A15 are always
00110000, while bits A5-A 7 are not standardized.
4.1.7.1 LEDs (Table 4-5) - The eight LEDs are all randomly accessible and individually latched. The
state of the latches on power up is not defined. Writes to binary addresses OOllxxxxxxxOyyyO will turn
off LED yyy. Writes to binary addresses OOllxxxxxxxOyyyl will turn on LED yyy. In addition, every
write to an LED latch resets the 4-bit BCD digit counter.

Table 4-5
Item

LA120 LEDs

Positions and Labels

Label

ON
LINE

Position

LOCAL

ALT
CHAR
SET

(blank)

CTS

DSR

SET-UP

PAPER
OUT

4.1.7.2 Seven Segment Display - The four 7-segment digits are addressed sequentially through a 4-bit
counter when a write is done to addresses 0011 xxxx xxxi xxxx. The counter is reset by writing an LED
latch (or it can overflow after 16 increments). Each write to a seven-segment digit increments the
counter, as well as sending segment data and turning on the selected digit. The 16 states of the counter
are shown in Table 4-6.

4-7

Table 4-6 Seven Segment Display Countr
Counter Value

Digit

0000
0001
0010
0011
0100
0101'

none - reset to this value by LED write
ones
tens
hundreds
thousands
none

1111

none - next increment wraps around to 0000

Data is sent to the seven-segment digits in address bits AO-A3 in inverted BCD. For example, if
AO-A3 are 1111, a zero will be displayed, if 1110, one, etc. The special value 0000 displays a blank. The
. digit currently selected will remain intensified until the counter is incremented or reset. In order to
display a multidigit number" the firmware sends data sequentially to the four digits at a high enough
rate to avoid perceived flicker.
4.1.8 Non-Volatile Memory
Memory references to binary addresses 0110xxxxxxxxxxxx will access the ER-1400 non-volatile memory. Each such reference will have one wait state inserted. The ER-1400 is a serial memory, with a
capacity of 100 14-bit words. The microprocessor talks to it through three general-purpose control
lines, assigned to address bits A8-AI0, a clock input on AO, and a data/address read/write line in data
bit D7.
The ER-1400 only operates when the firmware supplies it with a clock in the frequency range of about
11-18 kHz. While bit-banging the clock, the firmware manipulates control lines and data line to
perform the basic operations shown in Table 4-7.

Table 4-7 Non-Volatile Memory Operations
Control
Lines

Operation

000
001
010
011
100
101
110
111

Standby
Read
Erase
Write
Not used
Shift data out
Accept address
Accept data

4-8

All data and address transfers to and from the ER 1400 non-volatile memory are done in bit serial
fashion using a single data pin. Timing for the clock signal is generated by the firmware program and
depends on instruction execution times. To address a word in the non-volatile memory, the program
presents two consecutive 10-bit addresses (total = 20 bits), which have been already decoded into two
l-of-l0 codes, corresponding to the row (ten's address) followed by the column (unit's address).
Example: Address 60 - 0001000000 - 0000000001
The electromechanical portions of the LA120 are placed in a quiescent state with interrupts disabled
prior to accessing the non-volatile memory. This allows the timing of the firmware-generated clock
signal to be precise. Because interrupts are disabled, the non-volatile memory access routines continue
to track the print head using a polling technique, thus preventing any possibility of losing track of print
head position.
4.1.9 DC305 Printer Controller
Memory references to addresses 0111 xxxx xxxx xxxx will select the DC305 printer controller. Address
bits A2-A 11 are ignored for both reads and writes; AO and A 1 are also ignored in reads. One wait state
is generated for each access to the DC305. Write accesses must be at least 7 JlS apart; there is no
restriction on reads. Most writes to the DC305 pass additional sub addressing data in the data field.
A full description of the DC305 is given in Paragraph 4.2.
4.1.10 8251A USART
All I/O to ports OxxxxxOx accesses the 8251A USART. The USART itself decodes address bit AO, so
that if AO = 0 a data port is accessed, while if AO = 1 a control/status port is accessed. By convention,
the LA120 firmware uses the lowest valued I/O port numbers. The USART ports are as shown in
Table 4-8.

Table 4-8

8251A USART Ports

Input/ Output

Port

Function

Input
Output

Oxxx xxOO
Oxxx xxOO

Received Data Buffer
Transmitted Data Buffer

Input
Output

Oxxx xxOI
Oxxx xxOl

Status Flags
Mode/Command Control

The 8251A requests an interrupt whenever RxRDY (receiver ready) is asserted. If no other interrupts
are pending, this will result in a RST 7 interrupt. Reading the received data buffer resets RxRDY and
thus the interrupt request.
LA120 firmware checks the USART transmitter status via TxE (transmitter empty), not TxRDY
(transmitter ready). This avoids an extra character time latency in sending XON/XOFF commands.

4-9

4.1.11 Utility I/O Ports
I/O addresses Oxxx xxIx select utility I/O ports. These consist of one 6-bit input port and one 6-bit
output port. The outputs are reset by the power-up sequence. Bit assignments of these ports are given
in Table 4-9.
Table 4-9

Utility I/O Ports

Port

Data Bit

Function

Input

0
1
2
3
4
5
6
7

Clear To Send
Ring Indicator
Option Present Indicator: 0 = option present
Loopback Gate Indicator
(not used)
(not used)
Secondary Received Line Signal Detect
Received Line Signal Detect

Output

0
1
2
3
4
5
6

Data Terminal Ready
(not used)
(not used)
Loopback Enable
(not used)
(not used)
Baud Rate Clock Division Factor
(0 = 16, I = 64)
External Reset Signal

The loopback enable disconnects the received and transmitted data serial lines from the external interface and connects them together. It is not currently tested or used by LA120 firmware.
4.2 DC305 PRINTER CONTROLLER
The DC305 printer controller performs functions that are beyond the capabilities of the microprocessor and provides an interface between the microprocessor and the printer electromechanical
components.
4.2.1 Dot Print Control
When there is at least one character to print, the microprocessor loads print head dot pattern data into
a buffer whose output selects head drivers to be activated. When carriage speed and position are
appropriate for printing, the microprocessor enables printing and enables the dot interrupt.
Print head motion signals from the carriage position encoder are combined with horizontal pitch SETUP data from the microprocessor to trigger a countdown timer that allows selected head drivers to be
turned on. At the termination of the count, the drivers are turned off and the buffer advances. When
there is room for more dot pattern data in the buffer, a dot interrupt is generated, requesting that the
microprocessor load more dot data into the buffer. When there is no more data to be printed, the
microprocessor disables the dot interrupt. When the buffer becomes empty, printing ceases.

(
4-10

4.2.2 Carriage Position Count
Print head motion signals consist of a pair of asynchronous logic levels whose states change in quadrature to each other (00, 01, 11, 10,00) as the carriage moves. After synchronization, the state changes
accumulate in an 8-bit binary up/down counter as carriage position. The microprocessor periodically
reads the counter to track carriage position over the entire width of the carriage and to determine
carriage speed.
4.2.3 Carriage Speed Control
The voltage supplied to the dc motor is controlled by a pair of pulse streams. The first pulse stream has
a duty cycle that is proportional to the binary value of a microprocessor-supplied speed command. The
second pulse stream has a duty cycle that is proportional to the frequency of print head motion signal
state changes (i.e., motor speed). The integrated pulse streams are subtracted to yield the motor voltage. A steering circuit interchanges the roles of the two pulse streams to provide direction control as a
function of the directions of the speed command and the motor speed.
4.2.4 Line Feed Control
The line feed stepper motor is controlled by a two bit state word that controls the polarity of the
voltage to each of the motor windings and a third bit that controls the amplitUde of the current in the
windings. Higher current is used to run the motor rather than to hold a steady position.
The timing of state changes during line feeding is completely under control of the microprocessor, with
the aid of a programmable timer interrupt that is made available by utilizing the countdown timer of
the dot print control circuit in a timer mode rather than in a printing mode.

4.2.5 Bell Control
Latches and gating logic enable the microprocessor to control the propagation of either a 4ll[) Hz
signal or a 2400 Hz signal to a small loudspeaker that supplies the bell function and acts as an audible
warning device. The microprocessor can also control the application of an ultrasonic chopping signal
to the bell drive signal that has the effect of reducing the energy content in the audio range and thus
acts as a volume control.
4.2.6 Frequency Generation
Many processes in the LA 120 depend on timing signals for proper operation. The master timing source
is the 18 MHz crystal that drives the 8224 clock. The 8224 clock provides a 2 MHz signal that is used
by the 8080A microprocessor, the 8251A USART, and the DC305 printer controller as their primary
timing inputs. The 2 MHz clock input to the printer controller is divided by 13, yielding approximately
153.6 kHz, which is the clock rate that is used to drive most of the sequential logic in the printer
controller. A divider chain produces 76.8 kHz, 38.4 kHz, 19.2 kHz, 9.6 kHz, 4.8 kHz, 2.4 kHz, and 1.2
kHz signals. A divide-by-3 circuit produces 400 Hz. The signals from 153.6 kHz to 1.2 kHz drive a bit
rate multiplier in the carriage speed control circuit to produce the signal whose duty cycle is proportional to speed command. The 400 Hz signal provides an interrupt to the microprocessor every 2.5 ms,
which allows firmware processes to run periodically and thus be capable of performing timing-dependent operations. A baud rate generator circuit further divides various outputs of the divider chain to
produce baud rate clock signals for the lower baud rates and the split baud rates. A baud rate selector
circuit allows the microprocessor to select various outputs of either the divider chain or the baud rate
generator to be supplied as baud rate clock signals to the USAR T.
4.2.7 Tick Alarm
To prevent a microprocessor failure from causing physical harm to power circuits or electromechanical components, the DC305 has a special monitoring function that requires the microprocessor to prove its integrity by sending a clear tick command every 2.5 ms. Failure to do this is
proof of malfunction and results in disabling most chip outputs. The DC305 powers up with tick alarm
activated so that outputs are disabled until a programmed initialization sequence has been completed.

4-11

4.2.8 Interrupt Vectors
The DC305 can request interrupts at either vector RST 5 or vector RST 3. If both interrupts are
requested, an interrupt to vector RST 1 results. The RST 3 interrupt is always due to the 2.5 ms (400
Hz) clock tick, while the RST 5 interrupt may be due to either the real-time clock timeout (typically
while line feeding) or due to the dot FIFO being half empty (during printing).
4.3

LA120 FIRMWARE OVERVIEW

4.3.1 Scheduling
Processes run at four priority levels: highest priority is interrupt level (with interrupts disabled), then
tick level, interlaced tick level, and (lowest) background level. Note that except for interrupt service
routines, interrupts are normally kept enabled. The hardware interrupt vector scheme subdivides interrupts into two priorities, with receiver ready interrupts below all others. Firmware then further divides
the higher level so that dot or timer interrupts take priority over tick interrupts.
Processes that run at background are the least time-critical, since background may be locked out by
higher priority processes for short periods of time. On the whole, though, background gets the lion's
share of processor time, typically more than 50 percent. Tasks that run in background include line
image formatting, print scheduling, SET-UP command interpreting, and the ANSI parser. All printing, slewing, and vertical motion is originally scheduled by background level routines, even though
executed at higher priority. When the processor is idle, it will be looping at background level.
Interlaced tick level processes execute periodically after noninterlaced tick. Every interlaced tick process runs once every 1, 2, 4 or 8 ticks, where a tick is 2.5 ms. This is accomplished by a round-robin
scheduler, where each of eight phases is executed, in turn, on successive ticks. Each phase runs to
completion before the next phase is begun. Examples of interlaced tick processes are the keyboard
handler, communications protocol handler, and display handler.
Noninterlaced tick processing is begun immediately after taking a tick interrupt; interlaced tick follows
its completion. Currently, servo control comprises all of noninterlaced tick processing. This level of
processing must be guaranteed to finish before the next tick interrupt comes along. N oninterlaced tick
now takes about 700 J.LS on average.
Interrupt service routines are the most time-critical and are kept as short and fast as possible. They
include the dot FIFO interrupt, timer mode interrupt, and USART receiver ready interrupt.
Processes like initialization and non-volatile memory handling require that interrupts be off while
running and thus effectively run at highest priority.
4.3.2 ROM Layout
Standard LA120 firmware occupies 10K bytes and thus normally lives in five 16K bit ROMs. The first
four ROMs are treated as a group (in anticipation of 64K bit ROMs) and consist of code and tables
judged low risk - that is, unlikely to change. The fifth ROM is reserved for high risk data. It is
primarily tables but does have some executable code as well.
To get the European/ APL options, a sixth ROM must be installed. The presence of this ROM is
flagged by its first byte of zero. When optional features are invoked, routines in the standard set of
ROMs test this byte to see if the options are enabled.
Each ROM has a one byte checksum. This requires that every byte in each ROM be fully defined.
Thus, the fourth and fifth ROMs have large sections of padding (all OFFH bytes) to fill up empty
spaces. Many tables also have smaller sections of padding contiguous with them. Because of this
padding and the checksums, any changes to the ROM patterns will usually require recalculating the
padding section sizes and checksum values.
4-12

4.3.3 RAM Layout
The LA120 has 2K bytes of RAM; The first lK is used for the input buffer, a circular queue used to
store characters received from the USART or that have been echoed locally. The next page (where a
page is 256 bytes starting on a mUltiple of 256) contains several small buffers, the stack, and the tab bit
maps. The page after that contains all non-volatile parameters and other variables. Thus, after an
initial LXI H,FOOONE is performed, usually only a MVI L,LOW FOOTWO is needed to reference a
second variable.
RAM locations are all written to zero at power-up time. If a location needs to be initialized to another
value, its initial value is contained in a list processed by a RAM initialization routine.
4.4 PRINT CONTROL FIRMWARE
One of the more complicated operations in the LA 120 firmware is the starting of the print operation
after a carriage return or tab. The DC305 chip will only begin the printing operation after it has been
given a print start command. This command will be executed at the next point at which printing can
legitimately be started. This section deals largely with the routines for ensuring that the print start
occurs under the proper conditions and at the proper point. In addition, a description of the control of
print speed to limit component heating is included at the end of the section.
4.4.1 Starting the Printing Operation
The task of starting the print operation is handled in two steps. The first step is to prepare the DC305
to begin printing. This is done once for every print start. On the next and subsequent ticks, tests are run
to see whether the carriage has arrived at the proper location to begin printing and that it is traveling at
the proper speed. These tests are repeated until printing begins.
The forward printing process begins by obtaining the first character to be printed from the line buffer
and loading its dots into the dot buffer. The first four sets of dots are then loaded into the FIFO of the
DC305 chip and the dot interrupt is enabled and the carriage is started on the approach to the starting
point of the print string.
The reverse printing process begins the same as that previously described, except that all operations are
for backward printing. The right-most character in the line is loaded into the dot buffer.
Print start is enabled by a print start command that is stored by the DC305 chip and printing begins
when the print head wires cross the boundary of the intercharacter space in either direction. To initiate
a forward print start properly, the command must be given before the impact point crosses from the
intercharacter space of the previous character into the cell of the character to be printed.
As a practical matter, the print start command is given only when the impact point is in the Safe Print
Start Zone and the carriage is moving in the proper direction. The Safe Print Start Zone begins three
transitions to the right of the left-hand cell boundary of the previous character and ends three transitions to the left of the intercharacter space of the same character cell as shown in Figure 4-4.

4-13

14------PREVIOUS CHARACTER ------I~-

CHARACTER
TO BE
--.
PRINTED

SAFE PRINT START ZONE
INTERCHARACTER
SPACE

INTERCHARACTER
SPACE

HEAD MOTION---I.~
MA-4705

Figure 4-4

Forward Print Start

This scheme ensures that print start is only executed when the impact point crosses the left-hand cell
boundary of the character to be printed. The scheme thus avoids premature print starts and print starts
in the reverse direction that might otherwise be induced by unintended motions in the reverse direction. Such undesirable print starts would cause the characters printed subsequently to be displaced.
Therefore, tests are made by the microprocessor to ensure that the carriage is traveling to the right at a
speed that does not exceed the print speed by more than a small amount, that the impact point is in the
Safe Print Start Zone, and that other conditions outlined below are met.
A.number of tests must be made before forward printing may actually start. The first test is to see
whether a vertical motion is in progress or pending, a cover is open, paper is out, etc. If any of these
conditions are true, the routine is aborted. Next, the direction in which the carriage is traveling is
checked. If it is negative, the routine is aborted; otherwise, the tests are continued by computing the
maximum permissible approach speed as a function of the print speed limit currently in effect. Then
the position counter is read and a projected impact point is computed. If the impact point is to the
right of the Saft Print Start Zone, the carriage has overshot the mark and the routine is aborted. If the
impact point is more than 255 transitions to the left of the right-hand border of the Safe Print Start
Zone, the routine exits and no further tests are made during this tick interval since there is time to do
the tests during the next tick interval. If the impact point is within range, the following tests are made:
1.

A check that the carriage speed is less than the maximum allowed,

A determination that the impact point is less than 34 transitions to the left of the right-hand
border of the Safe Print Start Zone,

A test that the print head is not likely to stop or change direction in the near future.

If any of the preceding tests are failed, printing cannot be started at the current tick time and the
routine exits; otherwise, a go ahead for printing is issued and a final test is made to ensure that the
impact point is to the right of the left-hand boundary of the Safe Print Start Zone. In the event that this
test is failed, the routine aborts. If the test is passed, the print start command is given to the DC305
chip and the address of the Dot Service routine is set up in the dot interrupt service routine and the
printing operation is finally begun.

4-14

The Safe Print Start Zone for a reverse print start is illustrated in Figure 4-S.

CHARACTER
TO BE
~~-------------------------PREVIOUSCHARACTER--------~~
PRINTED
SAFE PRINT START ZONE
INTERCHARACTER
SPACE

INTERCHARACTER
SPACE

+ - - HEAD MOTION
MA·4706

Figure 4-S

Reverse Print Start

The procedure for initiating a reverse print start is the same as that used for the forward print start,
except that direction of motion is from right to left instead of from left to right.
4.4.2 Flight Time Compensation
The flight time compensation procedure compensates for the fact that it takes approximately 400 J.Ls
from the time the command is given to a solenoid to print a dot until the print wire hits the paper. If
this command were to be given when the head is just at the point where the dot is to be printed and the
head were traveling at 18 in/s, the dot would be printed 0.0072 inch past the intended point. If the next
line were to be printed in the reverse direction, the characters would be displaced by a similar amount
in the opposite direction, so that the characters in two successive lines would be very noticeably misaligned. It can be seen that the amount of compensation needed is proportional to the carriage speed.
The faster the carriage moves, the earlier the wire has to be fired. Compensation is made by appropriate transition add or subtract commands sent to the DC30S printer controller. These commands cause
one transition to be added or subtracted from the transition counter in the chip so that the command
to fire is given to the solenoids before the intended print position is reached. The flight time compensation also compensates for some mechanical inaccuracies that are functions of print direction.
4.4.3 Dot Rate Limiting
The LA120 will print reasonable text at a rate of 180 char/s indefinitely. However, heavy printing,
such as many repetitions of the character "#" at 180 char/s without intervening spaces, will constitute
an overload. The reason for this is that each dot represents a certain amount of energy that must be
delivered and is eventually dissipated. If dots were printed too fast for too long a time, there would be
heating of the head and certain power supply components. The longterm printing rate pf the LA120,
therefore, is limited to 2200 dots per second. The necessary speed limiting is performed on the basis of
the recent printing history. The limiting function is a constant minus the integral of the difference
between the dotrate and the maximum rate. A speed limit is computed from this function which is
compared with the maximum permissible print speed for the current font. The lower of the two values
is subsequently used to limit the printing speed. The scheme takes into account the thermal mass of the
print head and of the power supply components and it allows heavy printing for a period of about 1
second. If the heavy printing continues, the print speed is reduced gradually until the dot rate is equal
to 2200 dots per second.

4- IS

4.5 CARRIAGE SERVO FIRMWARE
The carriage servo firmware ascertains the current position of the carriage and generates the speed
commands needed by the carriage servo to move the carriage to the position where it should be. Actual
and desired positions are determined every time a tick interrupt is received, which is every 2.5 ms. The
speed command given to the servo is then updated on the basis of these position determinations. This
command is such that the carriage servo moves the carriage toward the desired position as rapidly as
possible. As the carriage approaches the desired position, the speed is reduced to allow for a smooth
stop.
4.5.1 Transitions
The position of the carriage is measured by an incremental two-channel encoder mounted on the back
of the carriage servo motor. Each channel has a square-wave output with 660 cycles per revolution,
with the output of one channel leading the output of the other by 90 degrees. A transition is defined as
the change of the output of one channel from the logic "0" level to the logic" 1" level or vice versa.
Thus, there are two transitions per cycle in each channel and since there are two channels there is a
total of four transitions per cycle and 2640 transitions per revolution.
The motor moves the carriage 4 inches per revolution. Hence, there are 660 transitions per inch of
carriage motion and
1 Transition = 0.001515 inch
The carriage servo routines are entered every time a tick interrupt is received. The tick interrupt is
cleared and the actual position of the carriage is determined. Speed, flight-time correction, carriage
position, and error are determined. A real-time clock is also incremented.
4.5.2 Reading the Position Counter
Upon entry, the position counter in the DC305 chip is read. Interrupts are then enabled. The previous
reading of the position counter is retrieved and subtracted from the current reading of the counter. The
difference is stored for use in subsequent calculations. Since readings are made at fixed time intervals,
this difference is a measure of the carriage speed. The value of the current counter reading is stored for
use during the next tick interrupt service. This calculation is valid as long as the carriage did not move
more than 127 transitions during the preceding tick interval.
4.5.3 Carriage Speed Command
The determination of the command speed for the carriage servo is begun on the basis of how far the
carriage is from where it is supposed to be. The actual target speed for the servo is obtained from a
table lookup. This target speed is the speed input for subsequent routines where it is processed to
generate the actual servo command. The sign of the target speed is chosen so that the carriage moves
toward the point at which it is supposed to be and the target speed decreases as the carriage approaches
its destination so that it arrives there at a reasonable speed.
In general, the speed command is based on the target speed unless the change from the previous target
speed was too large. In that case, the acceleration limit is applied.
4.5.4 Error Conditions
A speed error is computed by comparing measured carriage speed with the target speed. If this error
exceeds a limit, it is an indication that the carriage is not moving as fast as it should and that it may, in
fact, be stopped completely. If the error exceeds the limit for many ticks in succession, it is presumed
that the carriage is stuck. This causes a pause flag to be set. Other pause flags are set when there is no
paper or when the cover is open. Before a speed command is sent to the DC305, the pause flags are
examined. If none are set, the speed command determined as previously described is sent. If any pause
flag is set, a speed command of zero is sent.

4-16

4.6 COMMUNICATION FIRMWARE
The LAI20 controls transmission and reception of data on its serial interface by the use of the modem
control lines to generate several full- and half-duplex protocols. SET-UP commands are used to fine
tune the various protocols to suit the various modem and remote end requirements.
4.6.1 Communication Modes
The LAI20 has a wide range of communication modes, and while none are highly complex in themselves, their number and subtle differences can be confusing. There are two basic full-duplex modes
and three half-duplex modes selected with the modem setup (M):
I.
2.
3.
4.
5.

Full duplex without EIA controls
Full duplex with EIA controls
Half duplex - supervisory control
Half duplex - coded control, EOT
Half duplex - coded control, ETX

Other SET-UP commands affecting communication control are break enable (U), secondary channel
(S), and auto disconnect (D).
4.6.2 Local Mode
Whenever the terminal is in local mode, all modem signals are unasserted. No calls can be generated or
received, and transmit and receive are disabled. All protocols except full duplex without EIA controls
start at this level.
4.6.3 Disconnects
Each of the following sections on full- and half-duplex modes define disconnects and the line functions
that can cause them within each protocol. Additional disconnects can be caused by situations within
the printer that cause printing to stop, such as paper out, cover open, or a head jam. Disconnect
generation is a function of the SET-UP commands break enable (U), XON/XOFF (X), and auto
disconnect (D) as shown in Table 4-10.
In all modes except M = I, a disconnect can be generated from the keyboard with a shift break. A long
break disconnect is generated which unasserts all signals and puts a space on transmit data for 3.5
seconds.
4.6.4 Full Duplex Without EIA Controls
This mode asserts DTR and RTS whenever the LAI20 is on-line and ignores modem signals to the
LA120. This mode, normally used for current loop, has receive and transmit enabled at all times while
on-line. The break and speed/restraint function, as described in "Full Duplex with EIA Controls," are
operational, but the disconnect functions are not.
4.6.5 Full Duplex with EIA Controls
This mode supports a full modem interface requiring the following conditions to be satisfied in order
to establish connection.
1.

DSR must be asserted; then the LA 120 asserts RTS.

RLSD must be asserted for at least 300 ms after DSR is asserted; then the LAI20 enables
transmission and reception.

This mode also provides automatic disconnect capability by use of the Data Terminal Ready signal.

4-17

Table 4-10

Disconnect Generation vs SET-UP Commands

SET-UP Commands

Auto Disconnect (D)
D=O

D = 1

Break Enable (U)
and
XON/XOFF Enable (X)

Action

X = 1
U = 0 or 1

XOFF Sent

x=o
U = 1

Break

X=O
U=O

No Action

X = 1
U = 0 or 1

XOFF Sent,
followed by
Disconnect

x=o
U = 1

Disconnect

x=o
u=o

Disconnect

4.6.5.1 Full-Duplex Break - A break can be generated manually by the break key or automatically by
a printer fault condition such as paper out. In full duplex, a break consists of asserting a space on the
transmit data line for 220 ms if transmission is enabled. If transmission is disabled, the break will
remain pending until transmission is enabled or a disconnect is generated.
4.6.5.2 Full-Duplex Disconnect - In order to cause the modem to disconnect from the telephone line,
DTR is deasserted for 80 ms. All signals are deasserted during this time, although it is the DTR signal
that the modem recognizes as a disconnect. There are three types of line-generated disconnects:
1.

Failure of either DSR or RLSD to assert within 20 seconds after the termination of a ring
indication,

Failure of RLSD to assert within 5 seconds after DSR when initiating a call,

After connection is established the assertion of RI, deassertion of RLSD for 5 seconds or the
deassertion of DSR.

In addition, an EOT received or transmitted with auto disconnect enabled will cause a disconnect.
When disconnect is initiated by the transmission of an EOT, sufficient time is allowed for the EOT to
be completely transmitted before the disconnect in order for the remote end to also disconnect. Also, a
long space disconnect can be generated from the keyboard. This produces a space on the transmit data
line and deasserts DTR for 3.5 seconds.

4-18

(

4.6.5.3 Restraint Mode - When a full-duplex mode is selected, the secondary channel setup (S = I)
selects restraint mode. The secondary request-to-send signal is used to control the reception data in the
same manner as XON/XOFF, although it cannot be controlled from the keyboard. This line is used to
signal the remote end to stop sending characters in order to keep the input buffer from overflowing due
to the receive character rate or a print stop condition (paper out, cover open, etc.). The remote end
must maintain the proper signals to have receive enabled before using the restraint line to control data
transmission.
4.6.5.4 Speed Control Mode - The speed control function is selected with SET-UP S=O in a fullduplex mode. While in this mode, the LA120 indicates its selected speed on the speed select line. The
signal is asserted if the operator-selected baud rate is 1200 or higher. This allows a high speed call to be
initiated from the LA120 without manually setting the high speed button on the modem.
Also, the LA120 will reset its operating baud rate to 1200 baud if the speed indicator signal is asserted.
The 1200 baud rate is forced only as long as the line is asserted and does not affect the operatorselected (displayed) baud rate.
4.6.6 Half Duplex
Due to the "one at a time" definition of half duplex, elaborate protocols (compared to full duplex) are
needed to define who should transmit at any given time. Each time the transmitter and receiver switch
functions, the line is "turned around." This basically consists of switching the end of the line that
asserts RTS, which reverses the transmit/receive mode of the modem and switches the carrier generation from one end to the other. Also, when echo suppressors are on the line, it is necessary to turn
them around in order to attenuate in the opposite direction. The LA120 incorporates three methods of
controlling line turnaround. In supervisory control mode the host controls all line turnarounds by
manipulating the secondary control lines. Reverse channel is mandatory for this mode. The two other
protocols (coded control with reverse channel and coded control without reverse channel) allow the
transmitting device to control line turnaround via specific control characters. If reverse channel is
used, these lines provide confidence as to the fate of the transmitted data. Without these signals, the
transmission is "blind."
4.6.6.1 Initial Direction Determination - When the LA120 is initially put on-line (or at power up),
data can be neither transmitted nor received. When the terminal is called, RI will assert before DSR. In
auto answer mode, most modems answer the call (go off hook) before asserting DSR. However, some
modems allow DSR to assert after a couple of rings but before the call is answered. With this sequence,
the terminal attempts to establish receive mode. If the terminal operator is initiating the call, DSR
asserts when the modem is placed in data mode. Since DSR is asserted without RI, the terminal
attempts to enter transmit or receive mode, depending on the HDX initial state SET-UP command. If
the terminal attempts to enter receive mode and RLSD is not asserted within 5 seconds, the normal
timeout disconnect occurs.
4.6.6.2 Reverse Channel - The reverse channel transmits supervisory or error control signals. These
signals flow in the opposite direction to which data is being transferred. Due to the relative lower
bandwidth of the reverse channel (to the forward channel), it is not used for data exchange.
4.6.6.3 Request to Send Delay - As noted in the RLSD definition, the analog loopback option turns
around certain lines to the LA120:
1.
2.
3.

R TS asserted causes RLSD to be true.
SRTS asserted causes SRLSD to be true.
Receive data mimics transmit data (local copy).

4-19

For this reason, whenever RLSD or SRLSD is to be used, 300 ms must have lapsed since the local
driving force (RTS, SRTS) has been removed. Up until that time the signals do not represent the
remote end.
Also, RTS cannot be lowered until the last character is completely serialized (transmit complete).
4.6.6.4 Turnaround Characters - The turnaround characters (EOT or ETX) initiate the line turnaround when received or transmitted. To eliminate the need for the operator to generate the turnaround control code, the LA120 automatically sends the control code after RETURN or ENTER key
is typed, after sending the normal code for that key.
4.6.6.5

Half-Duplex Break - A break can be generated manually by the BREAK key or automat-

icaHy-by-a-printcr-fault-condition-such-as-papcr-out~'Fhere-are--three--cases-of-break--processin o ~n-half-

duplex:
1:

Transmit mode (RTS true) - The break is transmitted as a space on the transmit data line for
220 ms.

Receive mode (RTS false) - The break is transmitted as a space on the SRTS line for 220 ms.
When operating with "coded-no reverse channel," the break is ignored when in receive
mode.

While switching modes - If neither receive nor transmit is enabled, the break will not be
processed until a definite line direction is established.

4.6.6.6 Half-Duplex Disconnect - Hanging up the telephone to disconnect from the line is accomplished by dropping DTR for 80 ms and resetting all control lines to their initial state.
There are five line conditions that will cause a DTR disconnect:

Failure of either DSR or RLSD to assert within 20 seconds of the termination of a ring
indication.

Failure of SRLSD to assert within 5 seconds after DSR, when initiating a call with reverse
channel.

Failure of a line turnaround to complete within 5 seconds.

In coded control, deassertion of RLSD or SRLSD for 5 seconds without the turnaround
character. (If no reverse channel, only RLSD is monitored.)

After a valid line direction is established, the assertion of RI or the deassertion of DSR.

In addition, a command can be used to initiate a disconnect. An EOT or DLE-EOT from the keyboard
or line will disconnect the line. If EOT is used as the turnaround character, DLE-EOT is used as the
disconnect command. When a disconnect is initiated from the keyboard, the EOT or DLE-EOT is sent
to the remote end before the disconnect in order for the remote end to also disconnect. Also, a long
break disconnect can be generated from the keyboard. This produces a space on the transmit data line
and drops DTR for 3.5 seconds.

4-20

4.6.7 Communication State Control
The communications firmware consists of three modules and various pieces of code in other modules.
The controlling module is the communication handler that decodes the communication state table to
generate the protocols. The third dedicated module is the input scanner, which scans the input data
stream for characters that affect the communications protocol. These modules operate at tick level and
are always monitoring and updating the communication operation.
4.6.7.1 Communication State Table - This table consists of encoded input and output conditions that
reflect the protocol diagrams presented in a following section. Inputs consist of signal values from the
communication line (DSR, CD, etc.) and terminal functions (break request, etc.). Outputs are signals
that the LAl20 can assert (DTR, RTS, etc.) and terminal control (transmit disable, etc.). There is also
a real-time clock output (set timer) and input (time expired) that allows timing of functions in the
range of 20 ms to 90 seconds. Timed functions include breaks, turnarounds, etc.
Each set of input and output conditions is considered a state. When a state is entered, the outputs for
that state are invoked, providing a strict definitiqn of the communication line at that time. These
outputs are held until one of the inputs associated with that state is of the desired value, at which time
the pointer associated with the input is used to access a new state and new outputs are generated. These
states are linked in such a manner as to generate the various protocols.
The conditional branch entry is an addition to the state table entries. This type of entry does not
generate new outputs, but allows the linkage of states (and thus the protocol) to be modified according
to various SET-UP conditions. This ability to branch on SET-UP conditions allows communication
states to be shared between protocols. An example is that most protocols use the same series of answer
states and then branch after a connection is established to implement the actual protocol.
4.6.7.2 Communication Handler - The main function of the communication handler is to implement
state transitions as defined in the state table. There are also some functions that are always present (or
almost) and, therefore, are not carried in each entry of the table, but are handled as a parallel function
in the communication handler code. The communication handler is broken down into two execution
blocks that run at tick level. Each block is called alternately by the LAl20 scheduler every four ticks,
generating a total pass of the handler in 20 ms. In addition to these two blocks, there is the initialize
section of code that is called at power-up and when communication affecting setups is changed. The
functions included within the handler are:
1.
2.
3.
4.
5.
6.
7.
8.

Control LINE/LOCAL, DSR, and CTS keyboard lights
Gather inputs for table exit conditions
Control timer
Check for disconnects
Speed/restraint for full duplex
Compare exit conditions to valid exits for the state
Invoke new state outputs
Detect and process branch table entries.

Break Processing - Breaks are received via a break request flag, set outside the communication handler
due to keyboard action or a printer fault condition such as paper out. The break request is passed to
i the exit condition inputs if breaks are enabled and is implemented by a series of normal state transitions if the selected protocol uses breaks.

4-21

Disconnect Processing - A disconnect request flag is set outside the communication handler if the
appropriate code is received or transmitted, or a printer fault condition such as paper out occurs and
auto disconnect is selected. Disconnects are implemented by starting the protocol at its initial state
after any pending XON/XOFFs are sent. By forcing the initial state, modem SET-UP 1 (full duplex
without EIA controls) will not perform a disconnect because its initial state is with modem signals
asserted, although internal initializations, such as resetting the USART, will occur. For this reason, it
is always recommended to be sure that auto disconnect is not selected when using modem SET-UP 1.
A long break disconnect request causes a special state to be entered for the 3.5 seconds, then exited to
the initial state for the protocol in effect.
Turnaround Processing - A turnaround request flag is used by the coded control protocols to initiate a
line turnaround. The flag is set outside the communication handler by reception or transmission of the
appropriate control code for turnaround. This flag is placed into the input byte and is available as an
exit condition to be used if the protocol in effect uses turnaround characters. The flag is reset by the
communication handler.
Timer - The communication handler contains a software timer that can be set by an output value from
the state table. Each state that sets the timer carries an extra byte to define the duration. When the
countdown timer has expired, a bit in the input byte is set that can be tested as an exit condition and
the necessary states can be started to process the timeout. All time values mentioned in the state
diagram are implemented using this timer.
SRTS Flag - The SR TS flag is a byte containing the value of secondary request to send when in full
duplex. This byte is always ORed with the outputs from the table to set SRTS when a function outside
of the table (speed/restraint) needs to control that signal. The state outputs never assert SRTS while
the SRTS flag is controllingSRTS; when the table is controlling SRTS, the SRTS flag is always zero.
Restraint Processing - The restraint function is implemented if in full duplex and secondary channel
(S= 1) is selected. If any of the appropriate printer pause conditions are true, the SRTS flag is set and a
new value sent immediately.
Speed Indicator/Select Processing - Speed information is sent to the modem if in full duplex and SETUP s=o. The operator selected baud rate is used to define the value for the signal sent using the SRTS
flag and an immediate output.
Speed select to the LA120 is implemented whenever the value of secondary carrier is changed during
full duplex with SET-UP S=O. When this occurs, the proper baud rate is generated according to the
new value of the secondary carrier.
Branch States - These entries in the table do not generate any new outputs, but can change the state
pointer according to the value of the following setups:
1.
2.
3.
4.

Full duplex
Coded control
Supervisory channel
HDX initial state.

These conditional branch entries contain an index value that is used to generate the address of a
routine that will test the appropriate SET-UP status. If the routine returns with the zero bit set, the
address contained in this entry is used as the next state to go to, and generates those outputs.

4-22

Auto Answerback - This function allows the answerback message to be sent the first time the terminal
is transmit-ready after establishing a valid connection. When the transmitter is enabled, a flag is
checked to see if it is the first time; if so, the answerback message is sent.
4.6.8

Control Code Generation and Detection

.4.6.8.1 Input Scanning - The input scanner runs at tick level and scans the input buffer for characters
that are relevant to the communication functions. The scanner looks for EOT, DLE-EOT, and ETX
and sets the appropriate flag for the current operating mode of the LA120. The scanner keeps its own
pointer and is asynchronous to the normal input buffer processor. The scanning was deemed necessary
due to possible latencies in normal character processing when the buffer is full.
4.6.8.2 Transmit Scanning -Characters that have communication meanings are also scanned in the
transmit routine. The same characters are checked and processed as in the input scanner, but it is done
as each character is sent. Control codes that effect communications are never echoed within the terminal. The transmit routine also refreshes the USART command, sometimes generated by the communication handler.
4.6.8.3 Control Code Generation - Control codes generated from the keyboard are sent and scanned
normally. When a half-duplex coded control protocol is selected, the appropriate turnaround character is built into the carriage return transmit string to relieve the operator of this code generation. These
"automatic" codes are detected in the normal manner.
4.6.9 Functional State Diagrams
This section contains diagrams (Figures 4-7, 4-8, 4-9, and 4-10) that define the status of the communication signals and functions at anyone time and what causes a change from one state to another. The
communication state table is encoded from these diagrams.
In these figures, a state is an area of an ON and/or OFF function. These areas relate to which signal is
changed and to what value. Only the signals specifically set/reset within a state are affected. The N /C
state is one that has no change to the outside world but the exit conditions are now different.
Each exit path from a state has an associated condition typed next to it. If this condition is true, the
path is taken and the next state entered. Those exit paths with more than one condition require all
conditions to be true unless specifically separated by "OR."
The half duplex diagrams contain Note A and Note AI.
, Note A is not a state but a branch of the form shown in Figure 4-6.

YES
CONTINUE ON

RECEIVE MODE 1ST?
(SETUP Q=1 ?)
NO
ENTER STATE
LABELED A1
MA-4701

Figure 4-6

Note A Branch Form
4-23

Note Al identifies the state entered after originating a call and the operator has selected to enter
receive mode first.
As noted earlier, there are functions in parallel to the state diagrams such as disconnect request,
line/local, etc.
The fundamental flow is clockwise when turning the line around in half duplex. When put on-line, the
OFF 1, 2, 3 state is entered, requiring either RING or DSR in order to exit the state.

ON~2

I. .

OSR

ON-1

OSR

N/C

ON-2

>5S

>70MS

OFF1,2,5,6

>300MS
RLSO

20 S AFTER
RING
>300MS
RLSO

RING OR
NOT OSR OR
NOT RLSO>5S

ON 5,6
I~

BREAK
REQUEST

>233 MS

ON-4
KEY:

1)
2)

OTR
RTS

3)
4)

SRTS
SPACE XMIT

5)
6)

RECEIVE
XMIT

N/C CHANGE
MA-4697

Figure 4-7

Full Duplex

4-24

NOTE A1

ON -4
~

BREAK
REQ
>300 MS
SRLSD

ON-2
OFF- 5,3

> 233 MS

••

NOT SRLSD

ON-6

RING OR
NOT DSR
>5SEC

OFF - 1,2,3

OFF - 2;6

>5S

•

>70MS
t

...

NOTE A

. OSR

ON -1
>300 MS
RLSD

RING
>20S

N/C

NOT RLSO
~

DSR
AND
RLSD
RING OR NOT DSR

ON - 5,3
~

BREAK
REQUEST

>233 MS

OFF 3

KEY:

1) DTR
2) RTS

3) SRTS
4) SPACE XMIT

5) RECEIVE
6) XMIT

N/C)

NO CHANGE
MA-4696

Figure 4-8

Supervisory Control

4-25

ON-4
NOTE A1
BREAK
REQ
ON-2
OFF - 5,3

>300 MS
SRLSD

>233 MS

•
TURNAROUND..
CHAR SENT

ON -6

RING OR
NOTDSR

NOT SRLSD
>5S
>5SEC

OFF - 2,6

Io......--------IM OFF -

>5S
1,2,3 .....----"""'II~~

t>70MS
....

NOTEA

DSR

ON -1

>20S

N/C

DSR
NOT R LSD >5 S
AND
'. RLSD OR RING OR
- _........=--... NOT DSR

TURNAROUND
CHARACTER
RECEIVED

1 - - - - - - - - ' > 300 MS

ON - 5,3

•
>233 MS

RLSD
BREAK
REQUEST

OFF 3

KEY:

1)
2)

DTR
RTS

3)
4)

SRTS
5)
SPACE XMIT 6)

RECEIVE
XMIT

N/C)

NO CHANGE
MA-4700

Figure 4-9

Coded Control with Reverse Channel

4-26

ON-4
NOTE A1
BREAK
>233 MS
REO _.L..-_-'--_
TURNAROUND
>300 MS _

ON-2
OFF -5

ON - 6

CHAR SENT

OFF - 2,6

RING OR
NOT DSR
OFF - 1,2,3

....

>5S

•

• >70 MS
4-

_ DSR

NOTE A

ON -1
• RING

TURNAROUND
CHARACTER
RECEIVED

DSR
AND
RLSD

NOT RLSD
>5S
OR RING OR
NOT DSR

ON-5
>300 MS
RLSD

t
KEY:

1)
2)

DTR
RTS

3)
4)

>20S

N/C

STRS
5)
SPACE XMIT 6)

RECEIVE
XMIT

N/C) NO CHARGE

MA·4698

Figure 4-10

Coded Control Without Reverse Channel

4-27

4.7 ESCAPE SEQUENCE PROCESSING
Escape sequences are processed by a table-driven parser. There are two major tables that are used in
parsing escape sequences, a state transition table and a jump table.
4.7.1 Escape Sequence State Transition Table
The escape sequence state transition table consists of seven individual tables or elements numbered 1
through 7. At any given time, there is a pointer in RAM that points to one of the elements in this table.
Each element of the table is used (at different times) to scan the next character in an escape sequence.
Basically, each element consists of one or more entries containing the following items:
1.

The character against which the input character is to be compared (either for an exact match
or lower than or equal for a "range" test).

A pointer to the next state transition table element to be used to test the next character of the
escape sequence if the test in item 1 succeeds.

An index into a jump table that provides the address of a routine to be executed if the test in
item 1 succeeds.

These entries can be broken down into two different types within each element of the table, depending
on how the first byte of the entry is used.
1.

The first byte of a table entry can be used to test for an exact match.

The first byte can be used as a "range" test. The range is satisfied if the input character from
the escape sequence is less than or equal to the first byte of the table entry.

All of the exact match table entries come first in the table element, and can be in any order (but are
arranged in ascending order for ease of maintenance.) The range tests come last in the element, and
must be in ascending order. The last entry in each element is a range test entry for octal code 377 to
force all of the remaining illegal characters through the parser. The two types of entries in each element
are separated by a zero byte. Figure 4-11 illustrates how the entries can be organized within each of the
table elements.
NOTE
The second type of element may have no exact
matches, so it starts out with a mid-table separator
(zero byte).

4-28

__
___
1--------1
~~~o

[--------1

MID-TABLE
SEPARATOR

zero
________

MID-TABLE
SEPARATOR

_-------1 RANGE

~=~=:=~=

TESTS
MA-4699

a. Type 1
Figure 4-11

b. Type 2

Entry Organization Within a Table Element

4.7.1.1 Element No.1 - This is always the first table used in parsing an escape sequence. The parser is
initialized to this element after a valid escape sequence has been parsed, whether the LA 120 actually
performs the designated function, or just skips over it. Prior to using this first table element, the
background executive routine has detected the first escape character denoting the start of an escape
sequence, and sets a flag so that any printable characters that follow will be routed to the parser. This
first element does the following functions:
1.

Strips out the escape sequences that are used to designate a GO graphic set by finding the left
parenthesis (octal code 050) after the initial escape character, and sets the pointer to element
no. 7 to parse the next character anticipated in these sequences.

Jumps to the appropriate action routines required to process each of the 2-character escape
sequences after finding the final character.

Strips out the 2-character escape sequences single shift 2 (SS2) and single shift 3 (SS3) and
the pointer to element no. 2 to parse the next character anticipated in these sequences.
NOTE
SS2 and SS3 are nonlocking shift-outs to predefined
graphic sets (like the SO control code), but only apply
to the next character in the sequence, then automatically shift back in again. Since the LA120 does not
support SS2 and SS3, it simply skips over the next
character.

Detects the start of four different types of control strings: device control string (DCS),
operating system command (OSC), privacy message (PM), and application program command (APC). It sets the pointer to element no. 3 to parse the next character anticipated in
these sequences.
NOTE
All control strings must be terminated by a string
terminator (ST), which consists of another escape
character followed by a backslash. Since the LA120
terminal does not support any control strings, it skips
over all of this.
4-29

Detects the start of a control sequence introducer (CSI), and sets the pointer to element no. 5
to parse the next character anticipated in this type of sequence. It also prepares to accept
multiple decimal input parameters.
NOTE
CSls (in 7-bit mode) consist of the escape character
followed by octal code 133 (left square bracket in
US/UK), a number of multidigit decimal parameters
separated by octal code 073 (semicolon), and terminated by a final character (octal codes 100-176).

Strips out all intermediate characters (octal codes 040 to 057)~ with the exception of 050 (left
parenthesis), which is used when designating graphic sets; and sets the pointer to element no.
4 to process the next character anticipated in these sequences.
NOTE
The LA120 terminal does not support any threecharacter (or longer) escape sequences that use intermediate characters except as previously noted.

Any other character received while in element no. 1 must be a final character. It is considered to be a valid 2-character escape sequence not implemented on the LA120. [By default,
this also includes a string terminator (ST) not immediately preceded by a control string.]
Therefore, the current sequence is considered complete, and the parser is reinitialized.

4.7.1.2 Element No.2 - This table element unconditionally skips the next character in the current
escape sequence, after which it reinitializes the parser. It is entered after encountering the start of a
single shift 2 (SS2) or single shift 3 (SS3) in element no. 1 or the start of a string terminator (ST) in
element no. 3.
4.7.1.3 Element No.3 - This table element is entered after finding the start of one of the four types of
control strings (DCS, OSC, PM, or APC) in element no. 1. It unconditionally skips all input characters, both intermediates and finals, until an escape character is encountered signifying the start of a
string terminator (ST). When the escape character is eventually found, it sets the pointer to element no.
2, which will skip over the final character of the string terminator. It also prevents the background
executive routine from sending another escape character.
4.7.1.4 Element No.4 - This table element is used to finish parsing an escape sequence in which an
unexpected intermediate character was encountered before the final character. It can be entered from
element no. 1 or element no. 7. It skips over any more intermediate characters until a final character is
found, after which it reinitializes the parser.
4.7.1.5 Element No.5 - This table element is used to process a control sequence introducer (CSI). It is
originally entered from element no. 1 after an escape character followed by a left square bracket (octal
code 133) has been encountered. The remainder of the CSI escape sequence will "loop" in this table
element until either the final character is found, or an error condition is detected. Errors are considered
to be characters in the octal code range of 072 to 077 (for example, a question mark or colon); or an
intermediate character (octal codes 040 to 057). Errors will cause the pointer to be set to element no. 6
to properly complete the parsing of this type of escape sequence.

4-30

ASCII digits that are encountered are considered to be part of a decimal parameter, and are appropriately processed. Semicolons that are found here are separator characters used between the parameters,
and are so processed.

If a final character is received by this table element, it jumps to the associated "action" routine. After
the final character "action" routine has completed, the parser is reinitialized. .
4.7.1.6 Element No.6 - This table element is entered after finding an illegal character while processing a CSI in element no. 5. The purpose of this table is to properly complete the parsing of this type of
escape sequence by skipping all additional characters until a final character (octal codes 100 to 176) is
found, after which the parser is reinitialized.
4.7.1.7 Element No.7 - This table element is entered from element no. 1 after finding the start of a
Designate GO Graphic Set escape sequence, which is an escape character followed by a left parenthesis.
If an additional intermediate character is found, the pointer will be set to element no. 4 to finish
parsing the remainder of the sequence correctly. If a final character is found corresponding to one of
the national character sets supported by the LA120, this table element will cause a jump to the "action" routine that changes the printer character set. If any other final characters (octal codes 060 to
176) are encountered, they will cause the parser to be reinitialized.
4.7.2 Escape Sequence Jump Table
The second major table used in parsing escape sequences is the escape sequence jump table. It consists
of a number of entries containing the addresses of routines to be executed when an exact match or
range test is satisfied by one of the table entries in one of the seven elements of the state transition
table. It is these routines that do the actual "work" required by the escape sequence, such as changing
variables, setting flags, etc .
. 4.7.3 Escape Sequence Parser
The parser is the set of routines that does the parsing or breakdown of an escape sequence. Three
routines control the logical flow of parsing an escape sequence:
1.
2.
3.

The routine that begins the parsing of escape sequences.
The routine that initializes the parser.
The routine that controls the flow through the state transition tables.

4.7.3.1 Begin Parsing - The begin parsing routine is called by the background executive routine that
is normally processing characters when it finds the first escape character that denotes the start of an
escape sequence. This routine starts the parsing routine by setting a flag that causes subsequent printable characters to be routed to the parser until the escape sequence has been terminated properly.
NOTE
Even though the parser is enabled, control characters
(octal codes 000 to 037) are skimmed off and acted
upon, and never get to the parser. With the exception
of device control strings (DeSs), if another escape
character is received before the current escape sequence has completed, the current escape sequence is
aborted and a new escape sequence will be started
with the second escape character. This is handled
outside the parser by the executive routine.

4-31

4.7.3.2 Initialize Parser - The initialize parser routine reinitializes the escape sequence parsing mechanism to start a new escape sequence as soon as the background executive routine encounters the next
escape character. This routine only does two things: it resets the parser flag (see Begin Parsing, Paragraph 4.7.3.1) and it resets the state table pointer to element no. 1.
This routine is called under the following circumstances:
1.

During power-up initialization.

After an escape sequence has been properly terminated or completed.

When a cancel or substitute character (or delete character in local mode) is encountered in
the input stream [(or when another escape character is encountered if not processing a
device control string (DeS)].
NOTE
The substitute character may be generated internally
if a communications error is detected. Terminating
an escape sequence when an error is encountered prevents the terminal from hanging in a nonprinting
state.

4.7.3.3 Flow Controller - The flow controller is a very short routine. The reason for this is that the
majority of the escape sequence parsing logic is contained in the state transition tables.
The flow controller consists primarily of two table look-up routines. When it is entered, the state
pointer is pointing to one of the seven elements of the state transition table that has been assigned to
examine the next (or first) character anticipated in the current (or next) escape sequence. The first of
the two table look-ups is looking for an exact match against the input character. This look-up is
terminated by either a "hit" (i.e., an exact match), or by finding the "mid-table" separator, which is a
zero byte.

If the mid-table separator was encountered first because there was not an exact match, the flow controller then proceeds to the second table look-up. The second table look-up is similar to the first table
look-up, except that a "hit" is considered to be any input character that is lower than or equal to the
first byte of a table entry. These "range test" table entries are in ascending order and are constructed so
that all input characters will get a "hit," including all erroneous ones.
Having gotten a "hit" with the first byte of a table entry from one of the seven escape tables, either as
the result of an exact match or a range test, the flow controller picks up the new pointer value from the
"matching" table entry. This designates the proper table element to use for the next character in the
escape sequence.
Next the flow controller picks up the jump index from the "matching" table entry, uses it to index into
the jump table, and jumps to the appropriate "action" routine.

4-32

4.7.4 CSI Parameters
The rules for CSI escape sequences allow any number of parameters: but in the LA120, only the last 16
are saved. Of the 16 (or less) that remain, they are processed in first-in, first-out (FIFO) order.
4.7.5 Control Strings
The following escape sequence~ are considered control strings: device control string (DCS), operating
system command (OSC), privacy message (PM), and application program command (APC). The
LA 120 does not support any control strings, but it will parse them correctly and skip over them. When
parsing control strings, the background executive routine will pass an escape character through to the
parser which it would not normally do. The escape character is needed to terminate the control string.
4.7.6 Final Character Perform-Function Routines
The actual performance of an escape sequence must wait until the "final" character has been received,
parsed, and interpreted before the actual desired function can be performed. The final character action
routines contained in the LA120 follow:
Horizontal Tab Set
Vertical Tab Set
Clear Horizontal Tab at Active Column
Clear Vertical Tab at Active Line
Clear All Horizontal Tabs
Clear All Vertical Tabs
Enter Alternate Keypad Mode
Enter Normal Keypad Mode
Index Down One Line
Next Line
Horizontal Position Absolute
Horizontal Position Relative
Device Attributes (Product ID)
Vertical Position Absolute
Vertical Position Relative
ANSI Tab Clears (0-4)
Set Mode (LNM)
Reset Mode (LNM)
Set Top and Bottom Margins
Set Left and Right Margins
Set Number of Lines Per Page
Set Multiple Horizontal Tabs
Set Multiple Vertical Tabs
Set Horizontal Pitch (char/in)
Set Vertical Pitch (lines/in)
Designate GO Graphic Set
4.8 SET-UP COMMAND PROCESSING
SET-UP commands allow many features of the LA 120 terminal to be controlled by the operator via
the keyboard. Rather than requiring the operator to enter a myriad of "free-form" commands with all
of the attendant checking that would be required by the firmware, it was decided to present the operator with a list of only the valid choices. Thus, the requirement of having to validate free-form commands was totally eliminated. The method chosen to present these selections was to display them
sequentially in the 4-digit, 7-segment display. The last choice displayed is the current selection.Entering an invalid SET-UP command will cause the audible alarm to sound.

4-33

4.8.1 SET-UP Command Implementation
To perform a SET-UP command, the operator must first place the LA120 in SET-UP mode using the
SET-UP key with or without the control key. While in SET-UP mode, the SET-UP LED indicator will
be flashing to confirm that the terminal is in SET-UP mode. In SET-UP mode, most of the keys on the
keyboard can be used to perform SET-UP commands.
While in SET-UP mode, printable characters go to the SET-UP routines, and control characters are
routed to the printer. SET-UP commands fall into two general categories:
1.
2.

Multiple choice SET-UP commands, and
Immediate action SET-UP commands.

4.8.1.1 Multiple Choice SET-UP Commands - Ifa SET-UP command has multiple choices, executing
the SET-UP command the first time displays the current setting of that function without changing it.
Executing the same SET-UP command a second or subsequent number of times without leaving SETUP mode (which is defined as releasing or unlocking the SET-UP key) will cause the display to cycle
through, one at a time, all of the valid choices for that command. After reaching the end of the
selection list, the display will recycle and start over again from the beginning.
The alphabetic keys ("A" to "z" in US/UK) are used to perform multiple choice SET-UP commands,
with the exception of "I" (Initialize) and "T" (printing self-Test). Alphabetic SET-UP commands
work the same, whether shifted or unshifted. Multiple choice commands are broken down into two
logical groups. All of the members of one group only have two choices. The number displayed in the
display is either a zero or one, which in general means that the selected function is either disabled (0) or
enabled (1). The fl.ags for these commands are stored as consecutive bits in RAM.
Multiple choice commands with more than two possible selections use an entire byte to store their
current setting. The value displayed is usually the value of this "index" byte plus one. These indices are
stored in consecutive bytes in RAM. There are four exceptions to displaying the index value plus one.
They are:
1.
2.
3.
4.

Receive Baud Rate (SET-UP 0)
Transmit Baud Rate (SET-UP Shifted 0)
Horizontal Pitch or char/in (SET-UP H)
Vertical Pitch or lines/in (SET-UP V)

Since the values being selected by these commands are displayable as decimal integers (suitably
rounded in the case of some horizontal pitches), these values are displayed instead of the index numbers. For example, if the "H" SET-UP command results in a display of "10," that means 10 char/in,
not the tenth choice in the list. Similarly a SET-UP "0" display of 1200 means a receive speed of 1200
baud.
4.8.1.2 Immediate Action SET-UP Commands - In an immediate action SET-UP command, the operator is not concerned with the current setting (if any). The operator just wants the terminal to do
something immediately. For example, to start the printing self-test, the operator uses SET-UP "T."
Sometimes the active position is an implied input to the action routine, such as in setting a horizontal
tab stop (SET-UP" 1"). The top row of the keyboard is assigned to the immediate action commands
with the exception of SET-UP "0" (receive baud rate) and SET-UP shifted "0" (transmit baud rate),
which are mUltiple choice.

(
4-34

Normally, the 4-digit, 7-segment display will contain the column number of the next character to be
printed. However, if the SET-UP key is pressed (or locked) and the SHIFT key is also pressed, it will
contain the current line number. 'For this reason, all vertical tab and margin commands have been
implemented as shifted. This makes them easier for the operator to set up. If the TOF (top-of-form)
command (SET-UP 4) is done shifted (and the top margin is clear), the operator will see the current
line n um ber change to "1."
The nonprinting self-test (SET-UP shifted» was assigned to the greater than character because on
both the US/UK and all other foreign keyboards this character has to be shifted to be entered, thus
reducing the likelihood of accidentally triggering this seldom-used command. The request for current
status message (SET-UP 8) cannot be entered shifted. This was done to eliminate some possible firmware interactions concerning the display that would have required additional ROM to solve. The
status message is "semi-recursive," and is described separately below.
The SET-UP routines also respond to numeric codes from the optional keypad, since the SET-UP
commands are defined by code rather than key position. The following three keys· are independent of
SET-UP mode: LINE/LOCAL, LOCAL FORM FEED, and LOCAL LINE FEED. The HERE IS
key is also controlled by the keyboard handler.
4.8.2 SET-UP Handler
Whenever the operator enters SET-UP mode, the background executive program invokes the SET-UP
handler for each character of the command whose octal code is greater than 040 (the space character)
and less than 177 (delete/rub out). If the character received is not from the US/UK keyboard, the SETUP handler translates the character into a code it would have received if the key had been struck on the
US/UK keyboard such that top row SET-UP commands, whose legends appear on the trim strip, do
not change position from character set to character set. Alphabetic SET -UP commands are not translated, so they are always identified by letter, not by key location.
The SET-UP handler's tables handle only octal codes 041 through 137 (which includes the uppercase
letters). Octal codes 140 through 176 (which include the lower case letters) are translated to the 041
through 137 codes. This is done to make the SET-UP commands independent of the SHIFT key or the
CAPS LOCK key. For example, the small letter "a" is translated to the uppercase "A."
The SET-UP characters are now used to access the first level command table. This table contains
information that identifies the class of SET-UP commands to which this command belongs. It is
possible that no SET-UP command at all is associated with this character (identified by a zero byte in
the table), in which case a bell is rung. Otherwise, the command will select one of several generalpurpose subroutines. Similar SET-UP commands that are in the same category are handled by the
same subroutines. Basically there are:

groups of commands that are on/off or 1/0 operations,

groups of commands that are multiple choices (like baud rates of 300, 600, 1200, etc.), and

groups of immediate action commands that do not alter parameters at all (like self-test,
save/recall, set tabs, etc.). These do not show results on the LED display.

4-35

Once the SET-UP command has identified the type .of action, subroutines are called to implement the
action. If the command is one of the on/off pr multiple-choice type, then the subroutine determines
whether the character has been typed once or several times in a row during this SET-UP sequence. The
first time a SET-UP command is typed, the value of the parameter's current setting is displayed. Upon
repeats of the command, the value of the parameter is altered and displayed on the LED display. For
each type of SET-UP command, there is a subroutine that handles the first input of the command and
a subroutine that handles subsequent SET-UP change commands. Finally, certain SET-UP commands
need to call an initialization subroutine every time the SET-UP command parametric value has been
altered (like moving the head slightly after changing horizontal pitch).
In summary, the basic input to the SET-UP command handler is a character coming from the keyboard. The other input to the SET-UP handler is the current parameter from the RAM. The SET-UP
handler output is the new value of the operating parameter. It also outputs new data to the numeric
display.
4.8.3 SET-UP /Keyboard Handler Relationship
Part of the work associated with SET-UP commands is performed by the keyboard handler. The
process of entering or leaving SET-UP mode is detected by the keyboard handler, which also controls
the corresponding LED indicator. While in SET-UP mode, printable characters go to the SET-UP
parsing routines, and control characters are routed to the printer. All other action associated with the
SET-UP functions is performed by the SET-UP handler with the exception of entering the answerback
message, which is performed by the keyboard handler. The SET-UP commands are code sensitive
rather than key-position dependent. Consequently, the SET-UP parsing routines also respond to numeric codes from the optional keypad. The following three keys are independent of SET-UP mode:
LINE/LOCAL, LOCAL FORM FEED, and LOCAL LINE FEED. The HERE IS key is also controlled by the keyboard handler.
4.9

CHARACTER PROCESSING

4.9.1 Character Reception
When a character is received and fully assembled by the USART, an interrupt is sent to the microprocessor. This interrupt is serviced by the character reception routine. This routine reads the character from the USART and checks for parity error. If a parity error has been detected by the USART,
the character is converted to a SUB character. If the character is neither NUL nor DI;:L (the all zeros
and all ones codes), it is stored in the input buffer in RAM to be processed by either the input buffer
scanner or the background executive routine.
4.9.2 Background Executive
Characters are processed by the background executive routine. The source of characters may be either
the input buffer or the local character slot, which may contain characters generated by the keyboard
either in local or SET-UP mode, or if local echo is enabled. The LOCAL FORM FEED and LOCAL
LINE FEED keys also use the local character slot, even when on-line.
When the background executive has a character to process, depending on the mode and state of the
terminal, it forwards it to one of the following processes:
1.
2.
3.
4.

Print Line Builder
Escape Sequence Parser
SET-UP Command Handler
Answerback Entry Handler

Processing of escape sequences and SET-UP commands has been covered in detail earlier in this
chapter. Building print lines and processing answerback entry is covered in the following paragraphs.

4-36

4.9.3 Print Line Builder
Printable characters are routed to the print line builder. Upon receiving a character, the first task
performed by the print line builder is to determine if it is a control character or a graphic character. If
the character is a control character, it is used to index a table of control routine addresses and an
appropriate control routine is executed. For example, routines are required for handling horizontal
and vertical tabs. They call other subroutines, which search a tab bit map table to find the first tab set
past the current printing position. Each routine returns with a value that specifies what the active line
or column should be when the routine has finished. If the character is a graphic character, it is moved
into one of two print line buffers, after a certain amount of processing.
The processing of a graphic character requires look-up tables to convert certain codes in the various
national languages to an internal code that will point to dot matrix representation of the character.
Also, if the printer is in the alternate character set, the character is converted so that it points into the
alternate character set dot table.
The print line buffer is then checked to ensure that the active column (the column in which the character is supposed to be deposited) is within the left and right margins. If it is outside these margins and
auto newline is enabled, the character is not deposited in the current print line. The current print line is
forced to be printed followed by a line feed. The active column is returned to the left margin. The result .
is as though a carriage return and line feed sequence was received just before the character. The
character is then put into the next print line buffer at the left margin. If the character is outside the
margin and the auto newline is disabled, the presence of the character means that printing is being
attempted beyond the right margin. The character is discarded and a low frequency bell is sounded.
Before attempting to deposit a character in the print line buffer, a test is made to be sure that a
character is not already in the buffer at the active column. If there is, an overprint condition exists.
Detection of an overprint prevents adding any more characters to the print line buffer until it has been
emptied (printed). A new 217-byte print line buffer is made available and the character is written into
the new buffer at the active column.
Depositing a character in a print line buffer causes the active column to be incremented by one. Tests
are performed to determine if the right margin warning bell should be sounded and to see if the right
margin has been reached. Other types of information stored in the print line buffers have to do with
producing vertical motion between lines and ringing the bell. Thus, a complete print line contains three
types of information: bell count, line feed step count, and character codes. The character codes are
positioned in the print line buffer at the same spot that they would appear on the paper. When a print
line buffer is full or its printing is forced (due to overprinting, etc.), then the print line buffer is given up
by the print line builder and traded for an empty print line buffer. When the full print line buffer is
acted on by the printing routines, it has to be prepared before it can be used to start printing characters.
When a line is to be printed, a decision has to be made as to which direction the line is to be printed. A
line is always printed forward unless it has vertical motion both before and after it. Also, a line is never
printed in reverse which contains overprinting (Le., a / and an 0 to make (1). Recall that a print line
buffer is forced to print when overprinting occurs. When forced to print, the buffer is swapped with the
empty buffer and the printing routines take over. Since the forced-to-print buffer is not full, it does not
have a vertical motion code at the end of the buffer. It has been sent to the printer because of overprinting, not because there is a terminating line feed character at the end of the line. Consequently, the
direction decision algorithm would find that this print line buffer did not have vertical motion both
before and after it.

4-37

If the print line buffer is a complete line bracketed by vertical motion on both sides, then the print
direction is decided by the direction algorithm. The algorithm remembers the last column printed on
the previous line. If the previous line had characters from columns 1 to 100 and was printed from left
to right, then the last column was 100. If the next line has columns from 25 to 125, the direction
algorithm finds which of the limits is closest to the last column of the previous line. In this example,
100 is closer to 125 than 25; therefore, the new print line is printed from right to left.
After the print direction has been established, it is necessary to look at the print line buffer in the
interval between the left-most and right-most characters to determine if a long sequence of empty
positions is in the print line. Otherwise, the interrupt routine would have to search through as many as
215 empty positions to locate the next printable character. To prevent this, the firmware performs a
housekeeping routine that scans the print line and converts the empty positions to real spaces (octal
code 40) or inserts a special tabbing command. The tabbing commands are interpreted by the printing
routine to indicate that there is a long sequence of white space; consequently, stop printing and start
slewing the print head. The routine also specifies where to stop slewing and again start printing characters. As an example, suppose a print line has characters from columns 1 to 10, then blanks from
columns 10 through 100, and characters again from columns 100 to 110. The housekeeping routine
would search the columns until it got to the blank in column 11. It would then start to count blanks. If
it finds five empty positions in a row, the routine leaves the printing mode and executes a high speed
slew to the next column in which characters will be found. When it finds the next character (in column
100), it will go back to column 11 and write a -1 value in that slot. This flags the column as the
beginning of a high speed slew. During printing, when the print routine encounters the -1, it causes the
print routine to stop and pass control to a high speed slew routine. The next column (12) contains the
address of the column (100) in which is located the next printable character. Thus, the "look-ahead"
housekeeping routine functions to speed up the rate of printing.
When the print line buffer is completely filled and the printing interrupt routine is free, the filled print
line buffer is' passed over to the background printing routine. If there are any bells specified in the print
line, the code is passed over to the bell handler routine, which will sound the bell at a 400 or 2400 Hz
rate at the proper time. If there are any line feed steps to be performed, the line feed routine will be
called, at the appropriate time, to index the stepper motor. Any characters contained within the print
line will call the printing routines, which will be scheduled at the appropriate column, and printing will
occur. When the print line buffer has been completely processed by the printing routines, an executive
routine pointer will exchange the empty print line buffer for the buffer just filled. The empty buffer will
be zeroed and returned to the background where it will start accepting new characters.
4.9.4 Answerback Entry Handler
When the LAI20 is in SET-UP mode and CTRL-HERE IS has been typed, a flag is set that causes the
background executive to pass all characters to the answerback entry handler. This routine builds a
string of characters in RAM to be used as the answerback message. The characters are echoed to the
printer by calling the print line builder. Control characters are echoed as "A" followed by the corresponding character from one of the uppercase alphabetic columns of ASCII, which has a code value 64
greater than the control character being entered in the string.
If more than 30 characters is entered, or SET-UP mode is exited during answerback entry, the string of
characters is not stored in the non-volatile memory, although it does function as the answerback string
until power is cycled or answerback entry is performed again.
If CTRL-HERE IS is typed while performing answerback entry, the answerback message is stored in
the non-volatile memory and subsequent characters are treated as SET-UP commands until SET-UP
mode is exited.

4-38

CHAPTER 5
TROUBLESHOOTING THE LA120

5.1 GENERAL
Table 5-1 lists the most common LA120 failures, the associated symptoms, and remedies. Check for
symptoms in the order given in Table 5-1. Refer to Figure 5-1 for location of logic/power board jacks
and cables. Table 5-2 lists the dc voltages and test points on the logic/power board.
When troubleshooting, ensure that all plug-in chips on the logic/power board are seated properly.
Improper initialization will probably result if any of these chips have worked loose in their sockets.
Keep in mind that whenever power is interrupted to the LA120, the terminal parameters are reinitialized to their stored values when power is applied.
In troubleshooting the LA120, use the applicable engineering logic drawings from the engineering
. drawing set. Also contained in the drawing set are unit assembly (UA) drawings that can be used for
component location on the logic/power board and the keyboard assembly. The LA120 IPB (EKLAI20-IP) can also be helpful.
WARNING
Use extreme care when checking internal portions of
the power supply due to exposed 120 Vac.
CAUTION
STATIC CAN DAMAGE COMPONENTS.
Logic modules contain static sensitive components.
Before handling any subassembly with logic components (removing or installing from LA120 terminal, removing from shipping package, bench
handling), touch the LA120 metal frame or some relatively large metal object, to remove static body
charges.

5-1

Table 5-1

LA120 Troubleshooting Procedure

Symptom

Probable Cause

Remedy

1. No power when POWER
switch is set to ON. Fan not
operating and no lights.

Main power fuse (F 1)

Check and replace fuse.

Not plugged in, no power at
wall socket

Check power cord, wall
socket.

Wiring between ac plug transformer and fan

Check and replace wiring.

Power supply fuse F3

Check and replace fuse F3.

Power supply

Replace power supply per Paragraph 6.21.

CVT power supply module

Replace CVT power supply
module per Paragraph 6.23.

Logic/power board

Replace logic/power board
per Paragraph 6.26.

Power supply

Replace power supply per Paragraph 6.21.

CVT power supply module

Replace CVT power supply
module per Paragraph 6.23.

Cable between J2 on power
supply and J2 on logic/power
board

Reconnect or replace cable.

Logic/power board

Replace logic/power board
per Paragraph 6.26.

DC motor/encoder cable to J 5
on logic/power board

Reconnect or repair cable.

DC motor/encoder or
logic/power board

Perform de servo test (Paragraph 5.2).

Encoder

Perform encoder duty cycle
check/adjustment (Paragraph
5.3).

2. Head slams into right
bumper and no bell sounds. *

3. Head slams into left bumper
and no bell sounds. *

4. Head slams into left or right
bumper and bell sounds. *

5. Head sla"ms into left or right
bumper after LA 120 has
warmed up.*

*Head slamming into bumper may cause CARRIAGE fuse (on logic/power board) to blow after a few seconds.

5-2

Table 5-1

LA120 Troubleshooting Procedure (Cont)_

Symptom

Probable Cause

Remedy

6. No response when power
switch is set to ON. Fan is operating but no lights.

5 A pico fuse F 1 (located on
CVT power supply module)

Remove power supply per
Paragraph 6.21 and replace
pico fuse Fl.

CVT power supply module

Replace CVT power supply
module per Paragraph 6.23.

Cable between J 1 on keyboard
and J 1 on logic/power board

Reconnect or replace cable.

Mate-N-Lok P5/J5 between
power supply and ac input

Reconnect or replace wiring.

Power supply

Replace power supply per Paragraph 6.21.

7. Display indicates 8888,

No paper

Replace paper.

print head does not move, and
all lights light.

Top cover open

Close cover.

Paper-out switch

Adjust or replace paper out
switch per Paragraph 7.4

J3 on keyboard

Reconnect J3. Check cable.

Cable between J2 on keyboard
and J 1 on logic/power board

Reconnect or replace cable.

Logic/power board

Replace logic/power board
per Paragraph 6.26.

Logic/power board

Turn LAI20 off, then back on.
If display continues blinking
replace logic/power board per
Paragraph 6.26.

Flashing 9 could indicate J2
on logic/power board or
power supply is disconnected

Reconnect J2.

8. Display indicates one blinking digit (0 through 9). Print
head does not move.

5-3

Table 5-1

LA120 Troubleshooting Procedure (Cont)

Symptom

Probable Cause

9. Print head does not move,
some lights light, display does
not indicate any number. Bell
sounds momentarily on
power-up and PAPER OUT
light blinks.

Carriage fuse
logic/power board

Remedy
F2 on

Replace fuse.

F2 on power supply

Replace fuse.

DC motor/encoder or
logic/power board

Perform dc servo test (Paragraph 5.2).

Logic/power board

Perform clock test (Paragraph
5.4).

Power supply

Replace power supply per Paragraph 6.21.

Cable to J5 on logic/power
board

Reconnect or repair cable.

10. Print head will not initialize properly. Light display
is erratic.

Power supply or logic and
power board.

Perform wake up test (Paragraph 5.5).

11. Print head moves left then
right a few spaces; however,
display indicates a number
other than 1 (number does not
flash).

Logic/power board

Replace logic/power board
per Paragraph 6.26.

Keyboard

Replace keyboard per Paragraph 6.20.

Cable between J2 on keyboard
and J 1 on logic/power board.

Replace cable.

Display or lights

To check display and lights
turn power OFF, open top
cover, then turn power ON.
Display should indicate 8888
and all lights should light. If
display is bad, replace keyboard per Paragraph 6.20. Replace lights as required.

12. Display does not appear to
work or lights appear to be
faulty.

NOTE
The following steps exercise the logic/power board
and the printing mechanism.
13. Press CTRL and SET-UP
to enter SET-UP. SET-UP
light does not blink.

Logic/power board or keyboard

5-4

While in LOCAL, press additional keyboard keys to isolate
fault between keyboard and
logic/power board. Replace
logic/power board or keyboard per Paragraphs 6.26 or
6.20.

(

Table 5-1

LA120 Troubleshooting Procedure (Cont)

-------------,.------------.,....------------...-.
Symptom
Probable Cause
Remedy
14. While in SET-UP, press T
to start self-test. Print head
does not fire in self-test mode;
however, carriage moves
across carriage bar.

Print head

Replace print head per Paragraph 6.3.

Print head· cable disconnected

Reconnect print head cable.

Logic/power board

Replace logic/power board
per Paragraph 6.26.

Carriage adjustment lever

Adjust print head using carriage adjustment lever.

Ribbon

Check and replace ribbon.

Ribbon chassis assembly

Check to see if ribbon moves
freely; if required, replace ribbon chassis assembly per Paragraph 6.18.

16. Missing dots or excessive
dots in characters.

Print head, print head cable,
or logic/power board

Perform print character test
(Paragraph 5.6).

17. Missing or incorrect characters (always the same character).

USART or ROM chip

Perform USART Test (Paragraph 5.7).

Keyboard

Perform keyboard test (Paragraph 5.8).

18. No line feed response from
one of the following keys.
Other two keys function normally.
• LINE FEED
• LOCAL LINE FEED
• LOCAL FORM FEED

Keyboard

Perform keyboard test (Paragraph 5.8).

19 . No line feed response from
any of the following keys:
• LINE FEED
• LOCAL LINE FEED
• LOCAL FORM FEED

Logic and power board or
stepper motor

Perform line feed test (Paragraph 5.9).

20. Bell does not sound during
self-test.

Logic and power board or
speaker

Perform bell test (Paragraph
5.10).

21. Bell sounds during self-test
but does not sound when
CTRL G is pressed.

Keyboard

Perform keyboard test (Paragraph 5.8).

15. No printout in self test;
however, carriage moves
across carriage bar and head
solenoids sound as if they are
firing.

5-5

Table 5-1

LA120 Troubleshooting Procedure (Cont)

Symptom

Probable Cause

Remedy

22. LA120 operates in selftest; however, printout is incorrect when operating with
user's equipment.

User equipment, 20 mA/EIA
interface, or logic/power
board

Connect 20 rnA or EIA loop
back connector to interface
cable. Place the LA 120 on-line
and type a few characters. If
LA 120 operates correctly,
problem is with users equipment. If LA120 does not operate correctly, replace EIA
interface cable, or logic/power
board per Paragraph 6.26. (If
20 rnA option is. used, replace
20 rnA cable or circuit board.)
Perform USAR T test (Paragraph 5.7).

USART
Modem

Replace modem.

Incorrect SET-UP parameters.

Check SET-UP parameters.

Logic/power board

Replace logic/power board
per Paragraph 6.26.

Power supply

Replace power supply per Paragraph 6.21.

Encoder

Perform encoder duty cycle
check/adjustment (Paragraph
5.3).

24. Print varies in density from
dark to light or light to dark
across page.

Print bar out of alignment

Perform print bar adjustment
per Paragraph 7.9.

25. Print density varies randomly across page.

Ribbon

Replace ribbon.

Power board

Replace logic/power
per Paragraph 6.26.

26. Printing is always light in
the same spot.

Print bar pitted or bent printer
mechanism

Replace print bar per Paragraph 6.6 or printer mechanism per Paragraph 6.22.

27. Printing density progresively drops off to no impression when printing single
or mUltiple lines.

Ribbon drive assembly does
not move ribbon

Replace ribbon drive assembly
per Paragraph 6.11.

Print head screws that secure
head to carriage have worked
loose.

Adjust print head per Paragraph 7.1

23. Loss of position when
printing multiple" lines.

5-6

board

Table 5-1

LA120 Troubleshooting Procedure (Cont)

Symptom

Probable Cause

Remedy

28. Ribbon does not reverse.

Ribbon or ribbon chassis assembly

Check for eyelet on ribbon.
Replace ribbon or ribbon
chassis assembly.

Pushrod disengaged

Reconnect pushrod.

Paper path obstruction

Clear paper path.

Carriage adjustment lever

Adjust carriage adjustment lever.

Tractors

Replace tractors per Paragraph 6.15.

Head gap

Check and adjust head gap per
Paragraph 7.1

29. Paper jams.

LINE FEED STEPPER MOTOR
ENCODER (BLACK)

. AND BELL SPEAKER

~ 'PRINT HEAD (FLAT CABLE)
J

DC MOTOR (RED, WHITE)

POWER
SUPPLY

MA-2565A

Figure 5-1

Logic/Power Board Connectors

5-7

Table 5-2

DC Supply Voltages

Voltage
(V)

Tolerance
(V)

Logic/Power Board
Test Points
(Figure 5-1)

+5
+12
-12
+24
-24

±O.25
±O.6
±O.6
±2.0
±2.0

12-6
12-2
12-3
14-1,2,3
14-7,8,9

Note: All voltages measured with respect to ground.
5.2

DC SERVO TEST
1.

Disconnect power from terminal.

Remove printer housing (Paragraph 6.2.1) and tape down cover interlock. Open rear door.

Push carriage assembly to the extreme left and slip timing belt off dc motor pUlley.

Disconnect P5 from logic and power board. Connect + 5 V to dc servo motor via pins 1 and
2 of P5 (filter capacitors C47, C48, C49, - provide a +5 V source). Connect +5 V to pin I
(white wire) and ground to pin 2 (red wire). Apply power to terminal.

Check output of encoder per Paragraph 5.3.

Remove power from terminal. Connect channell of scope to pin 8 of E25 (MINUS L) and
channel 2 to pin 9 (PLUS L). Set up scope according to Figure 5-2.

Apply power to terminal. Check that dc motor is turning in a counterclockwise direction as
viewed from the front of the terminal. (If the timing belt were on, the print head would be
driven to the left.) Check for the waveform shown in Figure 5-2a. With a dc voltmeter, check
servo amplifier output on pin 2 (red wire) of 15. The reading should be about +23 V.

Reverse +5 V connection to P5 by connecting ground to pin I (white wire) and +5 V to pin
2 (red wire). The dc motor will turn in a clockwise direction. Change scope trigger source
from CHAN2 to CHAN I and check for the waveshape of Figure 5-2b. Check servo amplifier dc output on pin 2 (red wire) of 15. The dc voltmeter should read about -23 V. Remove
power and reconnect 11p5.

Remove scope leads. Slip timing belt onto dc motor pUlley. Close up lower rear panel and
install printer housing (Paragraph 6.2.2).

5-8

a. Motor Being Driven Counterclockwise

-- -

b. Motor Being Driven Clockwise
SCOPE SETUP
VOLTS/DIV:

5V CHANNELS 1 AND 2

VERTICAL MODE:

CHOP

SWEEP SPEED:

0.1 MS/DIV

TRIG MODE:

NORMAL

TRIG SOURCE:

CHAN 2, DC, INT, pas
FOR FIGURE 5-2A. CHANGE
TO CHAN 1 FOR FIGU RE 5-2B.
MA-4679

Figure 5-2
5.3

DC Servo Signals

ENCODER DUTY CYCLE CHECK/ADJUSTMENT
1.

Disconnect power from terminal.

Remove printer housing (Paragraph 6.2.1) and tape down cover interlock. Open rear door.

5-9

Push carriage assembly to the extreme left and slip timing belt off dc motor pUlley.

Check channel 1 output of the encoder by connecting channel 1 of the scope to pin 6 of E25
on the logic and power board. Apply power to terminal. The dc motor/encoder will rotate
continuously. Adjust scope for settings given in Figure 5-3 and check for waveshape shown.
The waveshape must show a 50 percent duty cycle (equal positive and negative alternations)
as measured from the center of the waveform jitter.

If encoder output is good, proceed to Step 8. If the duty cycle is not 50 percent, proceed to
Step 6.

Remove the two screws and the circular cover from rear of dc motor/encoder. If motor / encoder is the Hitachi model, the rear cover is square and is popped off instead of
unscrewed.

r---y,

MEASURE DUTY CYCLE FROM
CENTER OF JITTER

---y,

CYCLE--......

CYCLE---!

I
I
I
I
I
I

I
I
I
I

SCOPE SETUP
VOL TS/DIV:

VERTICAL MODE:

CHAN 1

SWEEP SPEED:

20 /-LS/DIV; ADJUST VARIABLE
SWEEP SPEED FOR ONE CYCLE
FI LUNG ENTI RE SWEEP

TRIG MODE:

NORMAL

TRIG SOURCE:

CHAN 1, DC, INT, POS
MA-4684

Figure 5-3

Encoder Output Waveform

5-10

Adjust channell adjustment (Figure 5-4) for a 50 percent duty cycle. Apply glyptol to the
potentiometer after adjusting.

Connect channel 1 of scope to pin 7 of E25 to check channel 2 output of the encoder. Check
for waveshape shown in Figure 5-3. The waveshape must show a 50 percent duty cycle as
measured from the center of the waveform jitter.

If duty cycle is not 50 percent, perform Steps 6 and 7 for channel 2 adjustment.

10.

With belt tension spring in place (Figures 6-5 and 6-6), press left-hand pulley against printer
mechanism and slip timing belt onto dc motor pUlley.

11.

Install printer housing (Paragraph 6.2.2).
r - - - - - - I C CHIP

CHANNEL2
ADJUSTMENT

CHANNEL 1
ADJUSTMENT

a. Litton, Clifton Precision Model

CHANNEL2
ADJUSTMENT--+--~

..M--f--IC CHIP

-----------CHANNEL1
ADJUSTMENT

b. Hitachi Model

MA-4702

NOTE:
THE ENCODER CIRCUIT BOARD MAY BE ORIENTATED IN ANY POSITION
0
AROUND A 360 CIRCUMFERENCE, NOT NECESSARILY AS SHOWN ABOVE.
THE CHANNEL 2 ADJUSTMENT IS CLOSEST TO THE IC CHIP ON THE CLIFTON
PRECISION MODEL AND FARTHEST FROM THE CHIP ON THE HITACHI MODEL.

Figure 5-4

Encoder Circuit Board

5-11

S.4 CLOCK TEST
The clock test checks the operation of the 18 MHz crystal and the 8224 clock chip E23.
1.

Check cp 1 and cp2 clock signals from E23 by connecting channel I of scope to pin II of E23
and channel 2 of scope to pin 10. Setup scope according to Figure 5-5 and check for waveshape shown.

Check that 8080A microprocessor is being clocked through its addressing sequence by connecting channel 1 of the scope to any of the sixteen output address lines. The address lines
out of the 8080A (E22) are designated AO through A15. Set up scope according to Figure 5-6
and check for waveshape shown. The waveshape will be unsteady due to address sequencing
of the 8080A.

Disconnect scope leads and close lower rear panel on terminal.

s.s WAKE UP TEST
1.

Remove power from terminal. Open lower rear panel.

Connect channell of scope to DC OK L at the junction of C52jC53 and R4 (bottom of R4
is most accessible). Connect channel 2 of scope to DC OK H at E23-2. Set up scope according to Figure 5-7.

..,.,

If'

• f-

~_L

r
J

.........

t'LL.

I
I.... _J

fff-

-I

--'-L

I.t!;t.-I

.- ,
I.L

--LL

, "~

li&._

SCOPE SETUP
VOLTS/DIV:

CHANNELS 1 AND 2 = 5V

VERTICAL MODE:

ALTERNATE

SWEEP SPEED:

O.2p.S/DIV

TRIG MODE:

NORM

TRIG SOURCE:

CHI, DC, INT, POS
MA-4687

Figure 5-5

c/J 1 and cp2 Clock Signals

5-12

·
II

SCOPE SETUP
VOLTS/DIV:

VERTICAL MODE:

SWEEP SPEED:

10 J,Ls/DIV

TRIG MODE:

NORM

TRIG SOURCE:

CHI, POS, INT*

* USE AC HIGH FREQUENCY REJECT.
MA·4676

Figure 5-6

8080A Addressing Output

I
I

SCOPE SETUP
VOL TS/DIV:

VERTICAL MODE:

SINGLE TRACE

SWEEP SPEED:

0.1 SEC/DIV

TRIG MODE:

NORMAL

TRIG SOURCE:

CHAN 1, DC, INT, POS
MA-4686

Figure 5-7

DC Wake Up Waveform

5-13

Apply power to terminal and check for waveshape of Figure 5-7. The DC OK L ramp
should be approximately 0.6 seconds. Turn power off and on to repeat the waveshape.
NOTE
Leave power off for about 10 seconds to allow for
capacitor discharge. Otherwise, the DC OK L ramp
will not occur when power is applied.

Remove power from terminal. Check RESET H by changing channel 1 of the scope to E231. Leave channel 2 input and set up as in Step 3. Apply power and check for the waveshape
of Figure 5-7.

Remove power from terminal. Disconnect scope leads and close lower rear panel.

5.6 PRINT CHARACTER TEST
The print character test checks print head operation and the circuits that process the character signal
prior to application to the print head. The slash character (j) is used for most of the waveforms shown
in this test. The slash is an ideal test character because it fires all seven wires in the print head and fires
them only once. Other characters would produce different waveforms according to which wires are
fired and how many times they are fired (see note in Step 4).
Sheet 5 of engineering drawing M7081 contains the print head schematic. In the upper right-hand
corner of the sheet is a 7-dot printed image showing the signal versus dot position relationship for the
seven print head wires. Use this image to determine which signal channel(s) are causing the faulty print
character. Examine the character to determine which dots are missing or which dots are firing too
often. Note on the logic print that each VDR head enable signal controls one-half of the print head,
while each DR drive signal controls only one channel.
1.

Remove power from terminal.

Using an ohmmeter, check continuity of print head solenoid in faulty channel. Check from
pin 3 (metal screw) of drive switch transistor (Q16, Q19, Q32, Q33, Q34, Q35 or Q36,
depending on which channel is faulty) to pin 3 of head enable switch transistor (Q30 or
Q31).
(This checks connector J /P6 and cabling along with print head solenoid.) The resistance of a
print head solenoid is about 2.5 ohms.

Connect channell of scope to output of the faulty channel of E25. Set up scope according to
Figure 5-8.

Apply power to terminal. Place terminal in local mode. Press and hold down the "I" key
and check for the waveform of Figure 5-8a.
NOTE
Due to the slash (I) character firing each wire once,
the waveshape of Figure 5-8a will be obtained for any
of the seven solenoid (S) signals from E25. If signal
SI (top of printed image) is viewed (E25-21) and uppercase "T" is pressed, the top wire will fire four
times producing the waveform of Figure 5-8b.

5-14

The Character "I"

...

---=v

The Character "T"

SCOPE SETUP
VOLTS/DIV:

VERTICAL MODE:

CHAN 1

SWEEP SPEED:

5 MS/DIV

TRIG MODE:

NORMAL

TRIG SOURCE:

CH1, DC, INT, NEG
MA-4689

Figure 5-8

Solenoid Signal Output of DC305

5-15

Connect channell of scope to drive signal output of the driver for the solenoid signal being
checked (DR output of E40 or E45). Connect channel 2 of scope to current feedback pin
(FB) of same driver. Use ac coupling for channel 2 input to scope. Set up scope according to
Figure 5-9.

Press and hold the" /" key and check for the waveform of Figure 5-9a. If print head solenoid is open, there will be no current feedback to driver (channel 2 on scope) and driver
output will be as shown in Figure 5-9b.

-n
I

...

Normal Waveform

Open Print Wire

SCOPE SETUP
VOLTS/DIV:

CH1 = 10V;CH2 = 2V*

VERTICAL MODE:

CHOP

SWEEP SPEED:

0.2 MS/DIV

TRIG MODE:

NORMAL

TRIG SOURCE:

CH1, DC,INT,POS

*USE AC COUPLING FOR CHANNEL 2 TO FLOAT SIGNAL
MA-4674

Figure 5-9

Drive Signal to Print Solenoid

5-16

(

Connect channel 1 of scope to head enable output of signal driver chip for solenoid signal
being checked [pin 9 (VDR) of E40 or E45]. Connect channel 2 of scope to drive signal
output pin (DR) of signal driver being checked. Set up scope according to Figure 5-10.

Press and hold the" /" key and check for the waveform of Figure 5-10.

Disconnect scope leads. Close lower rear panel.

.....
~

SCOPE SETUP
VOLTS/DIV:

CHI = 20V; CH2 = 10V

VERTICAL MODE:

CHOP

SWEEP SPEED:

0.2 MS/DIV

TRIG MODE:

CHOP

TRIG SOURCE:

CH1, DC, INT, POS
MA·4685

Figure 5-10

Head Enable vs Drive Signal

5.7 USART TEST
The USART test checks the 8251A USART, the I/O path to the user's equipment (LA120 portion),
and the transmit and receive clocks for various baud rates.
1.

Remove power from terminal and swing down rear cover panel.

Check baud rates by connecting channell of scope to E28-9 (TXC). Set up scope according
to Figure 5-11.

Apply power to terminal. Place LA120 in SET-UP mode and set in a baud rate of 50. Check
for 50 baud waveshape shown in Figure 5-11 a.

Set in the baud rates shown in Figure 5-11b through 5-11m and check for corresponding
waveshapes. Change horizontal sweep speed when indicated in figure.
NOTE

Note that TXC rate changes at 200 baud and at 7200
baud. Multiplier circuits within the USART are enabled at these frequencies to increase TX C to the
correct rate.
5-17

ill! III II! III

II11I1I1111111

a. 50 Baud, Sweep Speed = 0.1 ms

b. 75 Baud, Sweep Speed = 0.1 ms

IllJ ILHL

Ill, I, I,Ill II

c. Ito Baud, Sweep Speed = 0.1 ms

d. 134 Baud, Sweep Speed = 0.1 ms

U\
I

SCOPE SETUP
VOLTS/DIV:

e. 150 Baud, Sweep Speed = 0.1 ms

f. 200 Baud, Sweep Speed = 0.1 ms

g. 300 Baud, Sweep Speed = 0.1 ms

VERTICAL MODE:

CHAN 1

SWEEP SPEED:

AS NOTED FOR EACH WAVE FORM.

TRIG MODE:

NORM

TRIG SOURCE:

CHAN 1, DC, INT, POS
UA-4682

Figure 5-11

LA120 Baud Rate Clocks (Sheet 1 of 2)

III! 111111 III II! I! I
h. 600 Baud, Sweep Speed = 0.1 ms

IE:11L InlIIJ

III III L

ILid ±I LI

i. 1200 Baud, Sweep Speed = 5 p.s

ILiTITITIJ

j. 1800 Baud, Sweep Speed = 5 p.s

ILI~l Einld I L
SCOPE SETUP
VOLTS/DIV:

VERTICAL MODE: CHAN 1
SWEEP SPEED:

k. 2400 Baud, Sweep Speed = 5 p.s

l. 7200 Baud, Sweep Speed = 5 p.s

m. 9600 Baud, Sweep Speed = 5 p.s

AS NOTED FOR EACH WAVE FORM.

TRIG MODE:

NORM

TRIG SOURCE:

CHAN 1, DC,INT, POS
MA-4693

Figure 5-11

LA120 Baud Rate Clocks (Sheet 2 of 2)

Check RXC by connecting channell of scope to E28-25 and repeating Steps 3 and 4. The
RXC waveshapes at E28-25 are identical to TXC waveshapes at E28-9.

Clocks TXC and RXC are derived from ITC and IRC clocks out of the DC305 (E25-15, 14). The signal waveshapes at these points are identical to those in Figure 5-11.

Check USART I/O path as follows. Remove power from LA120. Wrap TXD EIA output
around to RXD input by jumpering pins C and E of J8 on logic/power board. Connect
channel 1 of scope to TXD output from USAR T (E28-19). Connect channel 2 of scope to J8
jumper. Set up scope according to Figure 5-12.

Apply power and place LA 120 in modem setting 1.* Press and hold
the waveform of Figure 5-12.

Connect channell of scope to RXD input to USART (E28-3). Leave channel 2 connected to
J8 jumper and do not change scope settings. Waveform should be as shown in Figure 5-12.

10.

Remove scope leads and close rear cover panel.

111111

key and check for

r
J

..'.

SCOPE SETUP
VOLTS/DIV:

CHANNEL 1 = 2V
CHANNEL 2 = lOV

VERTICAL MODE:

CHOP

SWEEP SPEED:

0.2 MS/DIV

TRIG MODE:

NORM

TRIG SOURCE:

CHAN 1, DC, INT, NEG
MA·4688

Figure 5-12

USART I/O Signals

LA 120 must be in modem setting 1 to remove enabling requirements imposed by EIA interface signals.

5-20

5.8

KEYBOARD TEST
1.

Remove power from terminal. Remove printer housing (Paragraph 6.2.1). Place LAI20 in
local mode. Proceed directly to Step 6 if faulty key/switch is one of the following:
SET-UP
RETURN
CTRL
CAPS LOCK

SHIFT
PAPER OUT (Switch)
COVER INTERLOCK (Switch)

Using keyboard schematic, note which scanning chip (E5, E6, EI01, EI02) is connected to
the nonfunctioning key. Turn over the keyboard bezel and connect channel 1 of scope to pin
1 of scanning chip.

Apply power. Set up scope according to Figure 5-13. The waveshape seen on scope (Figure
5-13) is due to keyboard scan and does not represent a signal condition. The waveshape will
be a steady pattern but may not exactly match that shown in Figure 5-13.*

Press the nonfunctioning key. The waveshape should change to an unsteadyt pattern similar
to that shown in Figure 5-14.

-_I
,.

... ... . L"

.. ~L
I

•
~

...

~'"

~It

••

-1-..

.- ~-

SCOPE SETUP
VOLTS/DIV:

VERTICAL MODE:

NORMAL

SWEEP SPEED:

10 J,Ls/DIV

TRIG MODE:

NORMAL

TRIG SOURCE:

CHAN 1,DC,INT,POS
MA·4676

Figure 5-13

Keyboard Scan Waveform

* The scope is triggered on a dc level. Pattern depends on which scan pulse triggers scope.

t The changing nature of the pattern is due to microprocessor program action.

5-21

r.--:

- _ ~.

SCOPE SETUP
VOLTS/DIV:

VERTICAL MODE:

NORMAL

SWEEP SPEED:

10 J,Ls/DIV

TRIG MODE:

NORMAL

TRIG SOURCE:

CHAN 1, DC, INT, pas
MA·4671

Figure 5-14

Keyboard Scan Waveform with Key Pressed

Connect channell of scope to pin on scanning chip that connects to nonfunctioning key. Set
up scope according to Figure 5-15. Press nonfunctioning key and check for waveform
shown. Trace circuit through key and J I, to KBD IN chip (E2) on logic and power board.
The waveshape of Figure 5-15 should also appear on the corresponding pin of E2. If proper
waveform is not obtained, check key and associated circuitry.

Check pin on scanning chip E8 that connects to nonfunctioning key/switch. The pin should
go to 0 V (ground) when key/switch is closed.

Connect channell of scope to pin 5 (KD7 L) of scanning chip E8. Set up scope according to
Figure 5-16. The waveshape seen on the scope (Figure 5-16) is due to keyboard scan and
does not represent a signal condition. The waveshape will be a steady pattern but may not
exactly match that shown in Figure 5-16.*

Press nonfunctioning key. The waveshape should change to an unsteady pattern similar to
that of Figure 5-16. Trace KD7 L through J2 and J 1 to KBD IN chip (E2) on logic and
power board. The waveshape of Figure 5-16 should also appear on pin 2 of E2.

*The scope is triggered on a dc level. Pattern depends on which scan pulse triggers scope.

5-22

--'" c.. .,

.....,

.....

SCOPE SETUP
VOLTS/DIV:

VERTICAL MODE:

CHAN 1

SWEEP SPEED:

10 ~s/DIV

TRIG MODE:

AUTO

TRIG SOURCE:

CHAN 1, DC, INT, POS
MA-4673

Figure 5-15

I~ 'r"
I'

I Y

-1

Key Circuit Waveform

, 'I

'I"' .1' 7'

IIf

--- -- -- -- .
I

1 :1

SCOPE SETUP
VOLTS/DIV:

VERTICAL MODE:

NORMAL

SWEEP SPEED:

5~ SEC/DIV

TRIG MODE:

NORMAL

TRIG SOURCE:

CHAN 1, DC, INT, POS
MA-4691

Figure 5-16

Keyboard Scan for Chip E8

5-23

5.9 LINE FEED TEST
The line feed test checks the printer LSI and the line feed amplifier (both on the logic/power board)
and the stepper motor.
1.

Remove power from terminal. Remove paper from terminal.

Jam paper into paper-out switch to override interlock.

Apply power to terminal.

Place terminal in local mode with LINE LOCAL key.

Connect channell of scope to pin 13 ofE25 on logic and power board. Connect channel 2 of
scope to pin 12. Set up scope according to Figure 5-17. Press LINE FEED and observe the
two channel inputs to the line feed amplifiers. Check that the waveforms are as shown in
Figure 5-17.

SCOPE SETUP
VOLTS/DIV:

5V, CHANNELS 1 AND 2

VERTICAL MODE:

CHOP

SWEEP SPEED:

2 MS/DIV

TRIG MODE:

NORMAL

TRIG SOURCE:

CHAN 1, DC, INT, pas
MA·4690

Figure 5-17

Line Feed Signal Output of DC305

Each phase of the quadrature phase, push-pull, line feed amplifier is checked by connecting
channel 1 of scope to amplifier channel input and channel 2 to amplifier output. Set up
scope according to Figure 5-18. Connect scope inputs according to Table 5-3. Press LOCAL
FORM FEED and check for waveform specified in table.

Check run signal of line feed amplifier by connecting channell of scope to E14-9 (amplifier
input) and channel 2 to pin 3 (collector) ofQl1 (amplifier output). Set up scope according to
Figure 5-19. Press LINE FEED and check for waveshape shown.

5-24

''-. ~.-

~io-.... ~

a. Phase 1 and 2

I
~-

~,,--.

......

b. Phase 3 and 4
SCOPE SETUP
VOLTS/DIV:

5V/DIV, CHANNEL 1
20V/DIV, CHANNEL 2

VERTICAL MODE:

CHOP

SWEEP SPEED:

2 MS/DIV

TRIG MODE:

NORMAL

TRIG SOURCE:

CHAN 1, DC, INT, POS
MA-4682

Figure 5-18

Line Feed Amplifier Input vs Output

5-25

Table 5-3

Line Feed Amplifier Test

Amplifier
Phase
Under Test

Scope
Channell

Scope
Channel 2

Waveform
Figure No.

Phase 1
Phase 2
Phase 3
Phase 4

E3-1
E3-5
E14-13
E14-11

Q15-3*
Q13-3*
Q14-3*
Q12-3*

5-18a
5-18a
5-18b
5-18b

*Pin 3 is the collector.

..,

. . .

.""\

SCOPE SETUP
VOLTS/DIV:

5V/DIV, CHANNEL 1
20V/DIV, CHANNEL 2

VERTICAL MODE:

CHOP

SWEEP SPEED:

5 MS/DIV

TRIG MODE:

NORMAL

TRIG SOURCE:

CHAN 1, DC, INT, POS
MA-4680

Figure 5-19
8.

Line Feed Run Signal

Remove power from terminal. Disconnect P7 to check stepper motor windings. Using an
ohmmeter, check between the following pins on P3:
1 and 2
2 and 3
6 and 7
7 and 8.
All four readings should be 7.5 ± 0.5 ohm.

Remove scope leads and close lower rear cover.

5-26

(

5.10 BELL TEST
1.

Apply power to terminal and initialize to the SET-UP parameters.

Place terminal in local mode with LINE LOCAL key. Open rear door.

Check input to bell amplifier by connecting channell of scope to pin 10 of E25 on logic and
power board. Set up scope according to Figure 5-20. Press CTRL G and check for the
waveshape of Figure 5-20a. A high volume bell should sound. Check low volume bell signal
by pressing SET-UP G and then CTRL G. The low volume bell will sound and the waveshape of Figure 5-20b should appear on scope. Press SET-UP G to return to high volume
bell signal.

,..-

,..-1-

-- - - a. High Volume

t ~,

lll~

....
1/1

,..

r--

...
-

~,.

b. Low Volume
SCOPE SETUP
VOLTS/DIV:

VERTICAL MODE:

NORMAL

SWEEP SPEED:

0.2 MS/DIV

TRIG MODE:

NORMAL

TRIG SOURCE:

CHAN 1, DC, INT, POS
MA-4683

Figure 5-20

Bell Amplifier Input
5-27

Check output of bell amplifier by connecting channel 1 of scope to junction of diode D2 and
R22 on logic and power board. With scope set-up as in Step 3, press CTRL G and check for
the waveshape shown in Figure 5-21. If a waveform is present but is not the proper shape,
speaker coil may be open. Perform Step 5 before replacing logic and power board.

Remove power from terminal. Disconnect P3. Check speaker coil by connecting an ohmmeter between pins 4 and 5 of P3. The reading should be 8 ± 2 ohms.

Reconnect P3 to J3 on logic board. Disconnect scope leads and close lower rear panel on
LA120.

- ,--..... - --L , l r-L.

-I-

SCOPE SETUP
VOLTS/DIV:

VERTICAL MODE:

NORMAL

SWEEP SPEED:

0.2 MS/DIV

TRIG MODE:

NORMAL

TRIG SOURCE:

CHAN 1, DC, INT, POS
MA-4681

Figure 5-21

Bell Amplifier Output

(
5-28

CHAPTER 6
LA120 SUBASSEMBLY REMOVAL AND INSTALLATION

6.1 GENERAL
This chapter contains information pertaining to the removal and replacement of the mechanical and
electrical subassemblies of the LA120.
Figure 6-1 lists all of the removal procedures in this chapter and the sequence in which these pro ..
cedures are performed. As an example, Figure 6-1 illustrates that to remove the power entry bracket
assembly, the power supply assembly removal procedure must be performed first.
DIGITAL Field Service recommends that the following LA 120 assemblies be replaced in their entirety
in a field environment.
Print head assembly (Paragraph 6.3)
Print head cable (Paragraph 6.4)
Timing belt (Paragraph 6.5)
Carriage assembly (Paragraph 6.7)
Ribbon drive pulley (Paragraph 6.10)
Ribbon drive assembly (Paragraph 6.11)
DC motor and encoder assembly (Paragraph 6.14)
Tractor drive shafts and tractor assemblies (Paragraph 6.15)
Idler gear assembly (Paragraph 6.16)
Stepping motor assembly (Paragraph 6.17)
Ribbon chassis assembly (Paragraph 6.18)
Keyboard/numeric pad assembly (Paragraph 6.20)
Power supply assembly (Paragraph 6.21)
Printer mechanism assembly (Paragraph 6.22)
CVT power supply module (Paragraph 6.23)
Power entry bracket assembly (Paragraph 6.24)
Fan (Paragraph 6.25
Logic/power board (Paragraph 6.26)
6.2 PRINTER HOUSING
The following procedure describes the removal and installation of the printer housing.
6.2.1

Printer Housing Removal
1.

Remove power from printer by disconnecting ac plug.

Remove printer paper and printer cover.

Remove six (6-32) self-tapping screws and flat washers that secure printer housing to cabinet
base (Figure 6-2) and set them aside.

6-1

PRINT HEAD
ASSEMBLY

PRINTER
HOUSING

LOGIC/POWER
BOARD

6.2

6.26

POWER SUPPLY
ASSEMBLY

DC MOTOR
AND ENCODER
ASSEMBLY

6.3

6.21

6.14
PRINT HEAD
CABLE

RIBBON DRIVE
PULLEY

6.4

6.10

TIMING
BELT

RIBBON DRIVE
ASSEMBLY

6.5

6.11
RIBBON
DRIVE
FAFNIR
BEARING

PRINT
BAR

6.6

6.7

6.8

PRINTER
MECHANISM
ASSEMBLY

6.22

6.15

IDLER GEAR
ASSEMBLY

6.16

KEYBOARD/
NUMERIC PAD
ASSEMBLY

CVTPOWER
SUPPLY
MODULE

6.23

6.20

6.12
CARRIAGE
ASSEMBLY
AND
FRONT
CARRIAGE
SHAFT

CARRIAGE
ECCENTRIC
BEARING
AND
LEVER

TRACTOR DRIVE
SHAFTS AND
TRACTOR
ASSEMBLIES

RIBBON
ECCENTRIC
AND
BACKSTOP
SPRING

6.13

STEPPING MOTOR
ASSEMBLY

6.17

POWER
ENTRY
BRACKET
ASSEMBLY

6.24
RIBBON
CHASSIS
ASSEMBLY

6.18

FAN
ASSEMBLY

6.25

REAR
CARRIAGE
SHAFT
AND
PLAIN
BUSHING

RIBBON
SPOOL
RATCHET
WHEELS
AND
FRICTION
DISKS

6.9

6.19
MA-2566A

Figure 6-1

Assembly Removal Sequence

6-2

2(6-32) SCREWS
(HIDDEN FROM VIEW)

HOUSING
(70-20024)

1(6-32)
SCREW

MA-2567

Figure 6-2
6.2.2

Printer Housing Removal and Installation

Printer Housing Installation
1.

Place printer housing on cabinet base and secure it with six (6-32) self-tapping screws and
flat washers.

Install printer paper and cover.

Restore power.

6.3 PRINT HEAD ASSEMBLY
The following procedure describes the removal and installation of the print head assembly. Refer to
Figure 6-3 during the procedure.

6-3

4(6-32) SCREWS

CARRIAGE
ADJUSTMENT
LEVER

CABLE CONNECTOR
(HIDDEN FROM VIEW)

PRINT HEAD
CABLE
(70-15384)
MA-2568

Figure 6-3
6.3.1

Print Head Removal and Installation

Print Head Assembly Removal
l.
2.
3.
4.
5.
6.

6.3.2

Perform printer housing removal procedure (Paragraph 6.2.1).
Remove ribbon.
Snap off print head heat shield.
Move carriage adjustment lever to the highest number (toward operator).
Remove the four (6-32) screws and washers that secure print head to carriage.
Disconnect print head cable connector from print head; then remove print head.
Print Head Assembly Installation

Connect print head cable to new print head.
CAUTION
When installing print head, check to ensure that timing belt teeth mesh (seat) with slots in the carriage.

Secure new print head with four (6-32) screws and washers. Make screws finger tight.

Move print head to the middle of print bar.

Set carriage adjustment lever to No. l.

6-4

(

Manually push print head forward until it touches print bar.

Check to ensure that timing belt is aligned with pUlley.

Tighten four (6-32) screws (10 ± 2 in/lb of torque).
CAUTION
Do not over-tighten the print head.

Install print head heat shield.

Replace ribbon.

10.

Slide carriage along carriage shaft to ensure that nothing is binding and that timing belt is
aligned with pulleys.

11.

Perform printer housing installation (Paragraph 6.2.2).

6.4 PRINT HEAD CABLE
The following procedure describes the removal and installation of the print head cable.
6.4.1

Print Head Cable Removal
1.

Perform printer housing removal procedure (Paragraph 6.2.1).

Perform print head assembly removal procedure (Paragraph 6.3.1).
CAUTION
Removing and installing the print head cable, without
removing print head, can damage print head connector.

3.
6.4.2

Disconnect cable from J6 (Figure 5-1) on logic/power board and remove it from cable
clamps.
Print Head Cable Installation

Install one end of cable as shown in Figure 6-4.

Dress the other end of cable down through slot in rear of cabinet, and connect cable connector to J6 on logic/power board.

Perform print head assembly installation procedure (Paragraph 6.3.2).

Perform printer housing installation procedure (Paragraph ~.2.2).

6-5

CABLE SLOT

BASE
OF

LA120
CABINET

r--

12%"

t·

10"4

MA-2571

Figure 6-4

Print Head Cable

6.5 TIMING BELT
The following procedure describes the removal and installation of the timing belt.
6.5.1

Timing Belt Removal
1.

Perform printer housing removal procedure (Paragraph 6.2.1).
NOTE
The print head ribbon cable does not have to be disconnected when performing the following procedure.

Perform print head assembly removal procedure (Paragraph 6.3.1).

Push carriage assembly to extreme left, and slip timing belt off dc motor pulley.
Timing Belt Installation

6.5.2
1.

With belt tension spring in place (Figures 6-5 and 6-6), press left-hand pulley against printer
mechanism and slip on the new timing belt.

Rotate timing belt screw (Figure 6-5) until it just touches ribbon drive assembly. Screws
should not exert pressure on ribbon drive assembly.

Perform print head assembly installation procedure (Paragraph 6.3.2).

Perform printer housing installation procedure (Paragraph 6.2.2).

6-6

BELT
TENSION SPRING

LEFT-HAND
PULLEY (12-12446)
RIBBON DRIVE
ASSEMBLY (70-11446)
MA-2569

Figure 6-5

Belt Tension Spring Location

6-7

Figure 6-6
6.6

Belt Tension Spring (Detailed View)

PRINT BAR

6.6.1

Print Bar Removal
1.

Perform timing belt removal procedure (Paragraph 6.5.1).

Move right-hand and left-hand tractors to their rightmost position.

Remove two 3/8 inch hex-head screws from the ends of the print bar (Figure 6-7a).

Remove print bar by carefully lifting left end of bar and moving it forward and toward the
left. Ensure that bar does not hit ribbon idlers on carriage assembly or lower edge of tractors.

6.6.2

Print Bar Installation
1.

Move the right-hand and left-hand tractors to their rightmost position.

Install print bar, right end first, being careful not to hit ribbon idlers on carriage assembly or
lower edge of tractors.

Install two 3/8 inch hex-head screws into the ends of the print bar.

Perform print bar adjustment procedure (Paragraph 7.9).

Perform timing belt installation procedure (Paragraph 6.5.2).

6-8

6.7 CARRIAGE ASSEMBLY AND FRONT CARRIAGE SHAFT
The following procedure describes the removal and installation of the carriage assembly and front
carriage shaft.
6.7.1

Carriage Assembly and Front Carriage Shaft Removal
1.

Remove power by unplugging LA120 power cord.

Perform printer housing removal procedure (Paragraph 6.2.1).

Unsnap keyboard bezel to enable easy access to carriage shaft clamp screws (Figure 6-7a).

Perform print head removal procedure (Paragraph 6.3.1).

Perform timing belt removal procedure (Paragraph 6.5.1).

Loosen two (8-32) front carriage clamp screws (Figure 6-7a).

Using a screwdriver, pry the top of the right carriage shaft clamp up and to the right as
shown in Figure 6-7b.

3/8 HEX HEAD SCREW
PRINT BAR

FRONT7

CARRIAGE
SHAFT

LOOSEN 8-32 FRONT
CARRIAGE CLAMP
SCREW(S) AT EACH
END OF THE
CAR R IAGE SHAFT

RIGHT PLATE
STIFFNER

a. Carriage Shaft Clamp Screws
MA-2590A

Figure 6-7 Carriage Assembly and Front Carriage Shaft
Removal and Installation (Sheet 1 of 2)

6-9

PRY THE TOP OF
THE RIGHT CARRIAGE
SHAFT CLAMP UP AND
TO THE RIGHT

MA-2591

h. Prying Up Carriage Shaft Clamp

BEARING

t------~=:J
CARRIAGE

LIFT THE RIGHT SIDE OF
THE CARRIAGE SHAFT UP
SLIGHTLY AND GENTLY
PULL BACK AND TO THE
RIGHT
MA-2592

c. Lifting Front Carriage Shaft

Figure 6-7 Carriage Assembly and Front Carriage Shaft
Removal and Installation (Sheet 2 of 2)

6-10

To remove carriage and carriage shaft, lift right side of the carriage shaft up slightly and
gently pull back and to the right as shown in Figure 6-7c.

Remove carriage from carriage shaft.

6.7.2

Carriage Assembly and Front Carriage Shaft Installation
1.

Place new carriage on carriage shaft.

Slide left side of carriage shaft into carriage shaft clamp.

Align carriage and bearing and snap the ,right side of the carriage shaft into carriage shaft
clamp. Ensure that carriage shaft clamp is seated properly.

Tighten left and right 8-32 carriage clamp screws, 18 ± 2 in/lbs of torque.

Holding belt tension spring in place (Figure 6-6), slip on the timing belt.

Replace keyboard bezel on cabinet base and secure by pressing in two sides of bezel to
engage mounting slots. Check keyboard connectors to ensure they are properly seated.

Perform timing belt installation procedure (Paragraph 6.5.2).

Perform print head installation procedure (Paragraph 6.3.2).

Perform the printer housing installation procedure (Paragraph 6.2.2).

6.8 CARRIAGE ECCENTRIC BEARING AND LEVER
Refer to Figure 6-8 during the removal and installation procedures.
6.8.1

Carriage Eccentric Bearing and Lever Removal
1.

Remove carriage assembly (Paragraph 6.7.1).

Remove carriage spring holding eccentric bearing in place. Spring is removed by pressing up
on spring while pushing spring tab toward rear of carriage assembly.

Remove eccentric bearing.

Pull lever off the end of the eccentric bearing.

6.8.2

Carriage Eccentric Bearing and Lever Installation
1.

Press lever onto end of eccentric bearing with stop detents facing in toward carriage assembly.

Place eccentric bearing in carriage assembly with lever dial toward top of carriage assembly.
Place oil on the eccentric bearing where carriage spring rubs against it.

Install carriage spring by pressing up on spring until spring tab snaps into place.

Install carriage assembly (Paragraph 6.7.2).

6-11

ECCENTRIC
BEARING

PUSH TO
REMOVE AND
TO INSTALL
MA·4507

Figure 6-8 Carriage Eccentric Bearing and Lever
Removal and Installation

6-12

6.9 REAR CARRIAGE SHAFf AND PLAIN BUSHING
Refer to Figure 6-9 during the removal and installation procedures.
6.9.1

Rear Carriage Shaft and Plain Bushing Removal
1.

Remove carriage assembly and front carriage shaft (Paragraph 6.7.1).

Separate ribbon chassis assembly from right end plate by removing 1/4 inch hex-head screw
and two Phillips screws.

Separate print bar from right end plate by removing 3/8 inch hex-head screw from right end
of the print bar.
NOTE
Try not to move print bar. Do not loosen screw on
left end of print bar.

Separate right end plate from printer frame by removing two 5/16 inch hex-head mounting
screws from underneath frame.

Carefully work right end plate toward the right until right end of the rear carriage shaft slips
out of right end plate. Support right end of the upper tractor shaft, which will slip out of its
bearing when right plate is moved.

Slide plain bushing off rear carriage shaft.

Carefully work rear carriage shaft out of left end plate.

MA-4508

Figure 6-9

Rear Carriage Shaft and Plain Bushing
Removal and Installation

6-13

6.9.2

Rear Carriage Shaft and Plain Bushing Installation
1.

Slip rear carriage shaft into shaft hole in left end plate.

Slide plain bushing onto rear carriage shaft.

Work right end plate into position while simultaneously inserting right end of rear carriage
shaft and right end of upper tractor shaft into right end plate.

Attach right end plate to printer frame by installing two 5/16 inch hex-head mounting
screws underneath frame.

Attach pr~nt bar to right end plate by installing 318 inch hex-head screw into right end of
print bar.
NOTE
Try not to move print bar.

Attach ribbon chassis assembly to right end plate with 114 inch hex-head screw and two
Phillips head screws.

Install carriage assembly and front carriage shaft (Paragraph 6.7.2).

Check print bar adjustment (Paragraph 7.9).

6.10 RIBBON DRIVE PULLEY
The following procedure describes the removal and installation of the ribbon drive pUlley. Refer to
Figure 6-10 during the procedure.
6.10.1

Ribbon Drive Pulley Removal

Perform printer housing removal procedure (Paragraph 6.2.1).

Slip timing belt off dc motor pulley.

Loosen 6-32 Allen-cap screw that secures collar clamp and drive pulley to ribbon drive shaft.
Remove collar clamp and drive pUlley.

6.10.2

Ribbon Drive Pulley Installation

Remove collar clamp from defective pulley and hand press it onto new drive pulley. Line up
front edges of collar clamp and drive pulley.

Replace ribbon drive pulley and collar clamp on ribbon drive shaft and adjust them to give a
clearance of 0.38 ± 0.03 inch between ribbon drive bracket and ribbon drive pulley. Tighten
6-32 screw to 12 ± 2 inllb of torque.

Slip timing belt onto pUlley.

Perform printer housing installation procedure (Paragraph 6.2.2).

6-14

PIVOT
TAB
UPPER PIVOT
POINT

RIBBON DRIVE BRACKET

0.38 ± .03 INCH (BETWEEN
PULLEY AND FRONT OF
BRACKET)

1.71 ± 0.02 IN.

t
FRONT END OF DRIVE PULLEY
AND COLLAR CLAMP SHOULD
TOUCH
COLLAR CLAMP
MA-2574

Figure 6-10

Ribbon Drive Pulley Removal and Installation

6.11 RIBBON DRIVE ASSEMBLY
The following procedure describes the removal and installation of the ribbon drive assembly. Refer to
Figures 6-11 and 6-12 during the procedure.
6.11.1

Ribbon Drive Assembly Removal

Perform printer housing removal procedure (Paragraph 6.2.1).

Remove ribbon spools and ribbon.

Slip timing belt off dc motor pUlley.

Lift up pushrod and remove retaining ring that holds pushrod in ribbon chassis.

Rotate ribbon drive pulley until clutch eccentric is at its highest point.

6-15

CLUTCH
ECCENTRIC
ECCENTRIC
TAB

RIBBON CHASSIS

/--....

(70-13859-00)
PUSH ROD
RETAINING RING

PUSH ROD SHOU LD
MOVE EQUALLY IN BOTH
DIRECTIONS WITH
RESPECT TO CENTER
OF HOLE

SPRING

MA-2572

Figure 6-11

Ribbon Drive Assembly Removal and Installation

Remove 8-32 screw and washer that secure ribbon drive to upper pivot tab on left-hand side
plate.

Remove ribbon drive by pulling out at top. This will free assembly from upper pivot tab.
Lift up on ribbon drive to clear lower pivot.

NOTE
The nut on the ribbon drive assembly is loose and can
be lost easily.
8.

Carefully remove ribbon drive assembly and pushrod.
6-16

PUSHROD
RETAINING RING

RAISED PORTION
OF PIVOT TAB

COMPRESSION
SPRING

FLAT WASHER

RIB ON
ECCENTRIC TAB
MA·2673

Figure 6-12
6.11.2
1.

Ribbon Drive Assembly (Detailed View)

Ribbon Drive Assembly Installation
Rotate the ribbon drive pulley on new ribbon drive assembly until clutch eccentric is at its
highest point.
NOTE
Ensure that PAPER OUT switch wires are under
pushrod when installing ribbon drive assembly.

Push pushrod through left-hand side plate.

Push rear of drive assembly toward side plate and engage lower pivot point.

Slide upper pivot under pivot tab on side plate and secure it with 8-32 screw and flat washer.
Make screw finger tight.

Replace retaining ring that holds pushrod in ribbon chassis.

Insert compression spring between left-hand side plate and ribbon drive.

Replace timing belt on ribbon drive pulley and dc motor pUlley.

6-17

Rotate ribbon drive and check pushrod travel to either side of center of the elongated slot in
the ribbon chassis. Travel should be equal on either side of center.

To attain equal travel from center, move ribbon drive upper pivot point in direction of the
shortest distance of travel. When travel is equal on both sides of the elongated hole, tighten
8-32 upper pivot screw to 18 ± 2 in/lb of torque.
NOTE
Check that eccentric tab is bent at a 90 degree angle
when viewed from the left side of unit. If angle is not
90 degrees, bend it to correct angle. This is done to
prevent tab from touching spring. Clearance should
be 0.254 to 0.508 mm (0.010 to 0.020 in).

10.

Replace ribbon and ribbon spools.

11.

Perform printer housing installation procedure (Paragraph 6.2.2).

6.12 RIBBON DRIVE FAFNIR BEARING
The following procedure describes the removal and installation of the ribbon drive Fafnir bearing.
Refer to Figure 6-13 during the procedure. To perform this procedure, the ribbon drive assembly must
be removed.
6.12.1

Ribbon Drive Fafnir Bearing Removal

Perform ribbon drive assembly removal procedure (Paragraph 6.11.1).

Loosen 6-32 Allen head screw that secures collar clamp and drive pulley to ribbon drive
shaft. Remove collar clamp and drive pulley (Figure 6-10).

Remove two (8-32) screws, nuts, and lockwashers that secure Fafnir bearing to ribbon drive
bracket.

Loosen 4-40 set screw that secures Fafnir bearing on ribbon drive shaft.

While rotating ribbon drive shaft counterclockwise, push shaft toward rear of ribbon drive
assembly until it clears ribbon drive bracket. (Always turn shaft in a counterclockwise direction when pushing through the one-way clutch.)

Remove Fafnir bearing from ribbon drive shaft and set bearing aside:

6.12.2

Ribbon Drive Fafnir Bearing Installation

Place new Fafnir bearing on ribbon drive shaft and push shaft toward pulley end of ribbon
drive until Fafnir bearing can be seated in ribbon drive bracket. (Always turn shaft in a
counterclockwise direction when pushing through the one-way clutch.)

Secure Fafnir bearing to ribbon drive bracket with two (8-32) screws, nuts, and lockwashers.
The nuts go on outside of ribbon drive bracket.

Slide ribbon drive shaft toward front of ribbon drive until it extends 1.71 ± 0.02 inch beyond
ribbon drive bracket (Figure 6-10). Tighten 4-40 set-screw in Fafnir bearing to 8 ± 1 in/lb of
torque. (The set-screw sets into a recessed dimple in Fafnir bearing split collar.) Turn shaft
in a clockwise direction to ensure freedom of movement.
6-18

RIBBON
DRIVE
BRACKET

RIBBON DRIVE
SHAFT
RIBBON
ECCENTRIC
MA-4694

Figure 6-13

Fafnir Bearing and Ribbon Eccentric
Removal and Installation

Replace ribbon drive pulley and collar clamp on ribbon drive shaft and adjust them to give a
clearance of 0.38 ± 0.03 inch between ribbon drive bracket and ribbon drive pUlley. Tighten
6-32 Allen head screw in collar clamp to 12 ± 2 injlb of torque.

Check that backstop spring coils do not overlap.

Perform ribbon drive assembly installation procedure (Paragraph 6.11.2).

6.13 RIBBON ECCENTRIC AND BACKSTOP SPRING
The following procedure describes the removal and installation of the ribbon eccentric and backstop
spring. Refer to Figure 6-13 during the procedure. To perform this procedure the ribbon drive assembly must be removed.
6.13.1

Ribbon Eccentric and Backstop Spring Removal

Perform ribbon drive assembly removal procedure (Paragraph 6.11.1).

Loosen 6-32 Allen head screw that secures collar clamp and drive pulley to ribbon drive
shaft. Remove collar clamp and drive pulley (Figure 6-10).

6-19

Loosen 4-40 set screw that secures Fafnir bearing on ribbon drive shaft.

Remove retaining ring that holds pushrod in rod end .

. 5.

While rotating ribbon drive shaft counterclockwise, push shaft toward rear of ribbon drive
assembly until it is completely removed. (Always turn shaft in a counterclockwise direction
when pushing through one-way clutch.) The fiber retaining ring will fall free. Support the
ribbon eccentric and backstop spring which is still attached to the eccentric tab.

Disengage backstop spring from eccentric tab.

Separate rod end, ribbon eccentric, and backstop spring.

6.13.2

Ribbon Eccentric and Backstop Spring Installation

Install (new) backstop spring on (new) ribbon eccentric. Apply one drop of No. 30 SAE oil
on spring and on eccentric. Engage backstop spring with eccentric tab.

Install rod end on eccentric.

Slide ribbon drive shaft through rear bearing, fiber retaining ring, ribbon eccentric, Fafnir
bearing, and ribbon drive bracket. (Always turn shaft in a counterclockwise direction when
pushing through the one-way clutch.)

Slide pushrod into rod end and replace retaining ring.

Replace ribbon drive pulley and collar clamp on ribbon drive shaft and adjust them to give a
clearance of 0.38 ± 0.03 inch between ribbon drive bracket and ribbon drive pulley (Figure
6-10). Tighten 6-32 Allen head screw in collar clamp to 12 ± 2 in/lb of torque.

Check that backstop spring coils do not overlap.

Perform ribbon drive assembly installation procedure (Paragraph 6.11.2).

6.14 DC MOTOR AND ENCODER ASSEMBLY
The following procedure describes the removal and installation of the dc motor and encoder assembly.
Refer to Figure 6-14 during the procedure.
6.14.1

DC Motor and Encoder Assembly Removal

Perform printer housing removal procedure (Paragraph 6.2.1).

Slip timing belt off dc motor pulley.

Open rear access door on cabinet.

Disconnect connectors from J5 and J7 on the logic/power board (Figure 5-1).

6-20

3 (8-32) ALLEN-CAP SCREWS AND HEX STANDOFFS

TIMING BELT
(12-11583)

ENCODER

MOTOR/ENCODER ASSEMBLY
(70-15388)

DC-MOTOR

MA-2575

Figure 6-14

5.
6.14.2

DC Motor/Encoder Assembly Removal
and Installation

Remove three (8-32) Allen-cap screws and hex standoffs that secure de motor to right-hand
side plate and remove motor.
DC Motor and Encoder Assembly Installation

Secure new de motor to right-hand side plate with three (8-32) Allen-cap screws and hex
standoffs. Tighten screws to 18 ± 2 in/lb.

Thread de motor and encoder cables down through slot at rear of cabinet.

Secure cables with cable ties where needed. Reconnect connectors to J5 and J7 on
logic/power board.

With belt tension spring (Figure 6-5) in place, press left-hand pulley against printer mechanism and slip on new timing belt.

Perform printer housing installation procedure (Paragraph 6.2.2).

6-21

6.15 TRACTOR DRIVE SHAFTS AND TRACTOR ASSEMBLIES
The following procedure describes the removal and installation of tractor drive shafts and tractor
assemblies. Tractor assemblies slip off the drive shafts once the shafts are removed. Refer to Figure 615 during the procedure.
_ _ TO FEED PINS

MA-2578

Figure 6-15
6.15.1

Tractor Drive Shaft and Tractor Assembly
Removal and Installation

Tractor Drive Shaft and Tractor Assembly Removal

Perform printer housing removal procedure (Paragraph 6.2.1).

Loosen tractor adjustments knob on both tractors.
NOTE
The spring clip on the outside of the lower tractor
support shaft is loose and may fall off when performing the following step.

Remove two retaining rings on left-hand side of tractor support shaft and drive shaft.

Slide both shafts to left about 10.16 cm (4 in) to remove the tractor assemblies. Pull shafts
(to the left) out of the left-hand end plate to remove shafts.

6-22

6.15.2

Tractor Drive Shaft and Tractor Assembly Installation

Replace defective tractor or drive shaft.

Slide two tractor shafts halfway through left-side plate.

Slide tractor assemblies on tractor shafts.

Ensure that index marks on outside of ~pper tractor bushings coincide with same flat on
square shaft (Figure 6-16). If bushings are not scribed, rotate tractors until a tractor pin on
both tractors is centered on the same flat.

ALTERNATE
TRACTOR

INDEX
MARK

TRACTOR
BUSHING

RIGHT HAND
TRACTOR
(12-11662-05)

TRACTOR PHASING
MA-2579

Figure 6-16

Tractor Phasing Adjustment

6-23

Position tractor shafts in side plates and secure them with three retaining rings.

Slide left-hand tractor from side to side. Ifit appears to bind or have excessive drag on the
shafts, grasp bottom tractor shaft and move it up or down in its slot until tractor slides easily
on shafts.

Slide left-hand tractor to left so that feed pins are 53.975 mm (2.112 ± 0.03 in) from lefthand side plate.

The right-hand tractor is adjusted to the width of paper or form to be used.

Perform printer housing installation procedure (Paragraph 6.2.2).

6.16 IDLER GEAR ASSEMBLY
The following procedure describes the removal and installation of the idler gear assembly. Refer to
Figure 6-17 during the procedure.
IDLER GEAR ASSEMBLY
(70-09694)

PAPER ADVANCE KNOB
(70-15389)
LEFT-HAND _ _+I
SIDE PLATE

0.002-0.007 IN.
BACKLASH AND EQUAL
DEPTH PENETRATION
MA·2582

Figure 6-17
6.16.1

Idler Gear Assembly Removal and Installation

Idler Gear Assembly Removal

Perform printer housing removal procedure (Paragraph 6.2.1).

Remove two (S-32) screws, lockwashers, and flat washers that secure idler gear assembly to
left-hand side plate.

6.16.2
1.

Idler Gear Assembly Installation
Secure new idler gear assembly to left-hand side plate with two (S-32) screws, lockwashers,
and flat washers. Make screws finger tight.
6-24

(

With idler gear in mesh with stepping motor gear and tractor drive gear, adjust idler gear to
achieve equal depth penetration and a backlash* of 0.0508 to 0.1778 mm (0.002 to 0.007 in)
between each pair of gears. The idler gear should be free to slide in and out. Rotate gears to
check backlash in several places.

Tighten two (8-32) screws to 18 ± 2 in/lb of torque.

Rotate paper advance knob to ensure that gears turn freely.

Perform printer housing installation procedure (Paragraph 6.2.2).

6.17 STEPPING MOTOR ASSEMBLY
The following procedure describes the removal and installation of the stepping motor. The idler gear
asembly must be removed to remove the stepping motor assembly. Refer to Figures 6-18 and 6-19
during the procedure.
6.17.1

Stepping Motor Assembly Removal

Perform printer housing removal procedure (Paragraph 6.2.1).

Perform idler gear assembly removal procedure (Paragraph 6.16.1).

Open rear access door.

Figure 6-18

Stepping Motor Assembly Removal
and Installation

*Backlash is the amount a gear turns prior to turning the gear it meshes with.

6-25

(8-32) SCREWS

MA-2584

Figure 6-19

Stepping Motor Mounted on Side Plate

Disconnect stepping motor from connector J3 on logic/power board (Figu.re 5-1) and clip
necessary cable ties. Disconnect speaker leads.

Pull wires up through slot at rear of cabinet.

Remove four (8-32) screws, flat washers, lockwashers, and hex nuts that secure stepping
motor to left-hand side plate. Set stepping motor aside.

6.17.2

Stepping Motor Assembly Installation

Secure new stepping motor to left-hand side plate with four (8-32) screws, flat washers,
lockwashers, and hex nuts. Install lower-left mounting screw first. The hex nut and lockwashers go on the inside of the left-hand side plate. Allow stepping motor to drop to its
lowest point in the elongated slots.

Tighten four (8-32) screws to 18 ± 2 in/lb of torque.

Reconnect connector to J3 on logic/power board. Secure stepping motor wires with cable
ties and thread them under printer mechanism and pushrod and down through slot at rear of
cabinet. Connect speaker leads to speaker.

Close rear access door.

Perform idler gear assembly installation procedure (Paragraph 6.16.2).

Perform printer housing installation procedure (Paragraph 6.2.2).

6-26

6.18 RIBBON CHASSIS ASSEMBLY
The following procedure describes the removal and installation of the ribbon chassis assembly. Refer
to Figure 6-20 during the procedure.

6-32 SCREWS
(BOTH SIDES)

RIBBON CHASSIS
( 70-13859-02)
MA-2580

Figure 6-20
6.18.1

Ribbon Chassis Assembly Removal and Ins~allation

Ribbon Chassis Assembly Removal

Perform printer housing removal procedure (Paragraph 6.2.1).

Remove ribbon spools and ribbon.

Remove retaining ring that holds pushrod in ribbon chassis.

Remove four (6-32) screws, flat washer, and star washers that secure ribbon chassis to rightand left-hand side plates.

Remove two (8-32) screws and washers that secure ribbon chassis to right- and left-hand side
plates.

Remove idler gear (Paragraph 6.16.1).

Remove stepping motor (Paragraph 6.17.1) and rest it on printer base.

6-27

COVER INTERLOCK SWITCH

WIRES DISCONNECTED HERE
MA-2581

Figure 6-21

Cover Interlock Switch

Remove cover interlock switch (Figure 6-21).

Remove ribbon chassis and set it aside.

6.18.2

Ribbon Chassis Assembly Installation

Secure ribbon chassis to right- and left-hand side plates with two (8-32) screws and lockwashers. Torque the screWs to 18 ± 2 in/lb.

Replace four (6-32) screws and lockwashers that secure ribbon chassis to right- and lefthand side plates. Torque the screws to 12 ± 2 in/lb.

Install stepping motor (Paragraph 6.17.2).

Install idler gear (Paragraph 6.16.2).

Line up hole in ribbon chassis with pushrod, and replace retaining ring that holds pushrod
in place.

Install cover interlock switch.

Install ribbon spools and ribbon.

Install printer housing (Paragraph 6.2.2).
(
I,

6-28

6.19 RIBBON SPOOL RATCHET WHEELS AND FRICTION DISKS
The following procedure describes the removal and installation of the ribbon spool ratchet wheel(s)
and friction disks. The ribbon chassis assembly must be removed first in order to remove the ribbon
spool ratchet wheel(s) and friction disks. Refer to Figure 6-22 during the procedure.
RIBBON
ECCENTRIC

SPOOL DRIVER
(LOCATED ON TOP)
COMPRESSION
SPRING
FRICTION
DISKS

REVERSE
SENSOR
STOP NUT
INTERPOSER
BAIL CAMMING
FOLLOWERS

MA-4509

Figure 6-22

6.19.1

Ribbon Spool Ratchet Wheel and Friction
Disk Replacement

Ribbon Spool Ratchet Wheel(s) and Friction Disk Removal

Perform ribbon chassis assembly removal procedure (Paragraph 6.18.1).

Measure distance (X) from stop nut to end of screw.

Remove stop nut.

6-29

Remove washers, compression spring, ratchet wheel, spool driver, and screw being careful
to note the order in which parts are removed. (See Illustrated Parts Breakdown for an
exploded view.)
NOTE
Before removing the ratchet wheel, note the direction
of the ratchet wheel teeth. When ratchet wheel is replaced, teeth must be orientated in the same direction.

Remove four old friction disks from ratchet wheel, spool driver, and ribbon chassis. Clean
each mounting surface.

Remove protective paper from four new friction disks and apply one each to spool driver,
ratchet wheel, and to each side of the ribbon chassis. Ensure that friction disk is applied to
the side of the ratchet wheel that faces the ribbon chassis. Ensure that surfaces are free of oil
and moisture.

6.19.2

Ribbon Spool Ratchet Wheel(s) and Friction Disk Installation

Replace screw, spool driver, ratchet wheel, compression spring, and washers. Ensure that
ratchet wheel teeth point in the proper direction as shown in Figure 6-22.

Replace stop nut. Adjust nut to position on screw noted in Step 2 of Paragraph 6.19.1.

Check ribbon tension adjustment (Paragraph 7.5). Readjust stop nut if necessary.

Perform ribbon chassis assembly installation procedure (Paragraph 6.18.2).

6.20 KEYBOARD/NUMERIC PAD ASSEMBLY
The following procedure describes the removal and installation of the keyboard/numeric pad assembly. Refer to Figure 6-23 during the procedure.
6.20.1

Keyboard/Numeric Pad Assembly Removal

Perform printer housing removal procedure (Paragraph 6.2.1).

Remove four (8-32) screws that secure keyboard to printer base.

To prevent scratching or damaging the keyboard, rest keyboard bezel on a piece of foam or
bubble plastic. Turn keyboard bezel upside down and remove four (8-32) screws and washers that secure keyboard/numeric pad bezel.

Lift keyboard/numeric pad and disconnect cable connectors as required.

6-30

e'i 8-32
lJ SCREWS

I !I
I

KEYBOARD BEZEL

\
TO PAPER OUT
SWITCH AND COVER
INTER LOCK SWITCH -=====!~

------l_

KEYBOARD

(5'4-1'2642)

TO
LOGIC/POWER
BOARD
MA-2585A

Figure 6-23
6.20.2
1.

Keyboard/Numeric Pad Removal and Installation

Keyboard/Numeric Pad ~ssembly I~stallation
Reconnect cable connectors to new keyboard/numeriC pad. Place pad on bezel and secure
with four (8-32) screws.
NOTE
The four-pin plug from the paper out switch and
cover interlock switcb can be ·inserted into J3· either
way.

Replace keyboard bezel on cabinet base and secure by pressing in the two sides of bezel to
.
engage the mounting slots. ,

Perform printer housing installation procedure (Paragraph 6.2.2).

6-31

6.21 POWER SUPPLY ASSEMBLY
The following procedures describe the removal and installation of the power supply. Refer to Figure 624 during the procedure.
J4 CONNECTOR

J2 CONNECTOR
POWER
SUPPLY

CONNECTORS

MA-2587

Figure 6-24

Power Supply Assembly Removal and Installation

(
6-32

6.21.1

Power Supply Assembly Removal

Remove ac power by unplugging LAl20 power cord.

Open rear access door on cabinet.

Remove ground wire on the side of the power supply by removing (8-32) screw, lockwasher,
and flat washer.

Disconnect connectors from 12 and 14 on logic/power board.

Loosen the two (8-32) screws at top of power supply, which will allow mounting plate to
slide down.
CAUTION
Placing. the full weight of the power supply on the
door can damage the door.

Tilt power supply toward door and disconnect Mate-N-Lok TM connector from power entry
bracket.

Carefully tilt out and remove the power supply.

TMMate-N-Lok is a trademark of AMP, Inc.

6-33

6.21.2

Power Supply Assembly Installation
CAUTION
Use care not to damage cables when installing power
supply.

Connect power supply Mate-N-Lok connector to power entry bracket and slide power supply into position as shown in Figure 6-25.

Figure 6-25

Power Supply Assembly in Position

Slide mounting plate into slot and tighten two (8-32) screws.

Reconnect connectors J2 and J4 to logic/power board.

Secure ground wire on the side of the power supply, by using 8-32 screw, lockwasher, and
flat washer.

Close rear access door on cabinet.

Restore power to LA120.

6-34

6.22 PRINTER MECHANISM ASSEMBLY
The following procedure describes the removal and installation of the printer mechanism assembly.
6.22.1

Printer Mechanism Assembly Removal

Perform printer housing removal procedure (Paragraph 6.2.1).

Remove ribbon spools and ribbon.

Remove the four (6-32) screws, lockwashers, and flat washers that secure print head to
carriage and set head aside (Figure 6-3).

Open rear access door.

Disconnect connectors from J3, J5, and J7 on logic/power board and clip necessary cable
ties (Figure 5-1). Pull disconnected wires up through cabinet base.

Remove the two (8-32) screws fastening the two ground wires to cabinet base (Figure 6-26).

Remove speaker wires from speaker.

Loosen the two (8-32) screws on the power supply, thereby causing mounting plate to drop.
Tilt power supply back to gain access to printer mechanism rear mounting screw. It is not
necessary to completely remove power supply assembly.

Remove the two wires from cover interlock switch (Figures 6-27 and 6-21).

10.

Remove the four (10-32) screws and washers that secure printer mechanism to cabinet base
(Figure 6-26) using a 5/16 inch nut driver.

11.

Carefully tilt printer mechanism up toward back of printer (Figure 6-26) and remove the two
leads from the paper out switch (Figure 7-4).

12.

Remove the two leads from the speaker and cut the cable ties holding the speaker leads.

13.

Carefully remove printer mechanism.

6.22.2

Printer Mechanism Assembly Installation

Remove the two ground wires from old printer mechanism and connect them to new printer
mechanism.

Place new printer mechanism on printer base and connect speaker, paper out, and cover
interlock leads. Secure leads as required with cable ties. Secure wire harness to base using
cable clamps.

Secure printer mechanism to base with four (10-32) screws and washers (Figure 6-26). Make
screws finger tight.

Thread cables and wires down through slots at rear of cabinet.

Secure connectors to J3, J5, and J7 on logic/power board (Figure 5-1).

6-35

PRINTER
MECHANISM
10-32
SCREW

10-32
SCREW
GROUND
WIRE

PRINTBAR
o

10-32 SCREW
FRONT FACE
OF PRINT BAR
IN LINE WITH
CENTER OF
REFERENCE
HOLE.
MA-2576

Figure 6-26

Printer Mechanism Assembly Removal
and Installation

Connect ground wires from printer mechanism to base with 8-32 screws (Figure 6-26).

Dress cables and wires inside the cabinet and secure cable harness, as required, to cabinet
using cable clamps.

Adjust position of printer mechanism (front to back) so that front surface of print bar
coincides with centerline of the reference holes in cabinet (Figure 6-27) within 0.030 inch.
Tighten the four (10-32) screws to 5 ± 1 in/lb of torque.

Perform print head installation procedure (Paragraph 6.3.2).

10.

Slide print head assembly across carriage shafts and check to ensure that carriage assembly
does not rub and is parallel to bent up flange (Figure 7-3). Loosen and readjust printer
mechanism if necessary.

6-36

(

REFERENCE
HOLE

COVER
INTERLOCK
SWITCH

REFERENCE
HOLE

FRONT FACE
OF PRINTBAR IN LINE
WITH CENTER
OF REFERENCE HOLE
MA·2577

Figure 6-27

Cabinet Reference Holes

11.

Carefully slide power supply back into position. Slide mounting plate through slot and
tighten the two (8-32) screws.

12.

Close rear access door on the cabinet.

13.

Replace paper in printer but do not feed it up into tractors. Pull paper up through cabinet
and printer mechanism to ensure that there is no drag on the paper. If drag is encountered,
perform printer mechanism and paper guide adjustments (Paragraphs 7.2 and 7.3). Remove
paper from machine.

14.

Perform printer housing installation procedure (Paragraph 6.2.2).

6-37

6.23 CVT POWER SUPPLY MODULE
The following procedure describes the removal and installation of the CVT power supply module.
Refer to Figure 6-28 during the procedure.
6.23.1
1.
2.
3.
4.

CVT Power Supply Module Removal
Remove ac power by unplugging LA 120 power cord.
Perform power supply removal procedure (Paragraph 6.21.1).
Disconnect cables from Jl and J2 on the CVT power supply module.
Remove the three (6-32) screws that secure CVT power supply module to power supply.
REGULATOR
BOARD
J2 CONNECTOR

{f!I

(54-13044)

J1 CONNECTOR

I~>3 (6-32) SCREWS

Figure 6-28

MA-2593

CVT Power Supply Module Removal and Installation

6-38

6.23.2
1.
2.
3.
4.

CVT Power Supply Module Installation
Secure new CVT power supply module to power supply using three (6-32) screws.
Reattach connectors to J 1 and J2 of CVT power supply module.
Perform power supply installation procedure (Paragraph 6.21.2).
Restore power to LA120.

6.24 POWER ENTRY BRACKET ASSEMBLY
The following procedure describes the removal and installation of the power entry bracket assembly.
Refer to Figure 6-29 during the procedure.
MATE-N-LOK
CONNECTOR

8-32 KEP NUTS

POWER ENTRY
BRACKET ASSEMBLY
(70-15168)
MA-2588

Figure 6-29

Power Entry Bracket Assembly Removal and Installation

6-39

6.24.1

1.
2.
3.
4.
5.
6.
7.
8.
6.24.2

Power Entry Bracket Assembly Removal
Remove ac power by unplugging LA120 power cord.
Unplug ac power cord from front of LA120 unit.
Open rear access door on cabinet.
Perform power supply removal procedure (Paragraph 6.21.1).
Disconnect Mate-N-Lok connector to fan.
Remove the three (8-32) nuts and captive washers.
Remove the one (8-32) screw, nut, and star washer securing ground wire to cabinet base.
Remove power entry bracket assembly.
Power Entry Bracket Assembly Installation

Mount power entry bracket assembly using three (8-32) nuts and captive washers.

Using the one (8-32) screw, nut, and star washer, secure ground wire to cabinet base; position wire adjacent to cabinet base metal frame.

Reconnect Mate-N-Lok connector to fan.

Perform power supply installation procedure (Paragraph 6.21.2).

Close rear access door on cabinet.

Reconnect ac cord.

6.25 FAN
The following procedure describes the removal and installation of the fan. Refer to Figure 6-30 during
the procedure.
6.25.1

1.
2.
3.
4.
6.25.2

Fan Removal
Remove power by unplugging LA120 power cord.
Perform power supply removal procedures (Paragraph 6.21.1).
Remove the four (8-32) screws, lockwashers, and flat washers from fan mounting bracket.
Disconnect fan Mate-N-Lok and remove fan.
Fan Installation

Install fan using the four (8-32) screws, flat washers, and lockwashers. Fan must be installed
with coil facing top of cabinet.

Connect fan Mate-N-Lok.

Place fan wires in cable clamp.

Perform power supply installation procedure (Paragraph 6.21.2).

6-40

FAN (12-12581)

MA-2589

Figure 6-30

Fan Removal and Installation

6.26 LOGIC/POWER BOARD
The following procedure describes the removal and installation of the logic board.
6.26.1

Logic/Power Board Removal

Remove power by unplugging LAI20 power cord. Remove printer paper.

Open rear access door on cabinet (Figure 6-31).

Disconnect all connectors from logic board (Figure 5-1).

Remove the seven (6-32) screws that secure the logic board to chassis. Remove by swinging
right-hand side of board out first.

6-41

MA-2586

Figure 6-31
6.26.2
l.

Logic/Power Board Removal and Installation

Logic/Power Board Installation
Place logic board on chassis (left-hand side first). Secure the board with seven (6-32) screws.
Tighten to 8 ± 1 in/lb.
NOTE
The four (6-32) screws in the heat sink are 0.5 inch
long, while the lower three (6-32) screws are 0.25
inch long.

Reconnect all connectors to logic/power board (Figure 5-1). Install connector Jl with beveled edge in upper left corner. Install connector J8 with red stripe on left. Install connectors
J3 and J7 so they are centered on jack.
CAUTION
Be sure to follow the cable orientations in Step 2.

Close rear access door on cabinet.

Replace printer paper and restore power to LA120.

6-42

CHAPTER 7
ADJUSTMENT PROCEDURES AND LUBRICATION

This chapter contains a detailed description of the following LA 120 adjustments and information on
lubrication.
Print head adjustment (Paragraph 7.1)
Printer mechanism adjustment (Paragraph 7.2)
Paper guide adjustment (Paragraph 7.3)
Paper out switch adjustment (Paragraph 7.4)
Ribbon tension adjustment (Paragraph 7.5)
Ribbon drive assembly adjustment (Paragraph 7.6)
Idler gear assembly adjustment (Paragraph 7.7)
Bumper assembly adjustment (Paragraph 7.8)
Print bar adjustment (Paragraph 7.9)
Lubrication (Paragraph 7.10)
7.1 PRINT HEAD ADJUSTMENT
The following procedure describes the print head adjustment.
1.
2.
3.
4.
5.
6.
7.2

Set power switch to off, and remove paper and ribbon.
Move print head to middle of print bar (Figure 7-1).
Loosen the four (6-32) screws holding print head (Figure 6-3).
Set carriage adjustment lever to no. 1 and position print head for contact with print bar.
Tighten the four (6-32) screws to 10 ± 2 injlbs of torque.
Replace ribbon and paper.

PRINTER MECHANISM ADJUSTMENT

Set power switch to OFF.

Perform printer housing removal procedure (Paragraph 6.2.1).
NOTE
Printer mechanism adjustment can be checked by going directly to Step 5.

7-1

SET TO NO.1

MA-2594

Figure 7-1

Print Head Adjustment

7-2

Loosen the two (8-32) screws on power supply, thereby causing mounting plate to drop. Tilt
power supply back to gain access to printer mechanism rear mounting screw.

Loosen the four (10-32) screws that secure printer mechanism to cabinet base (Figure 7-2).

Adjust position of printer mechanism (front to back) so that front surface of print bar is in
line with centerline of reference holes in cabinet (Figure 7-2) within 0.030 inch. Tighten the
four (10-32) screws to 5 ± 1 in/lb of torque.

Perform printer housing installation procedures (Paragraph 6.2.2).

PRINTER
MECHANISM
10-32
SCREW

10-32
SCREW

GROUND
WIRE

PRINTBAR

GROUND
WIRE

10-32 SCREW
FRONT FACE
OF PRINT BAR
IN LINE WITH
CENTER OF
REFERENCE
HOLE.
MA·2576

Figure 7-2

Printer Mechanism Alignment

7-3

7.3 PAPER GUIDE ADJUSTMENT
1.

Loosen the three (8-32) screws at bottom of paper guide and adjust for 2.54 to 3.556 mm
(0.10 to 0.14 in) gap between paper guide and bent-up flange of base (Figure 7-3).

Place paper in machine but do not feed it up into tractors. Pull paper up through cabinet and
printer mechanism to ensure that there is no drag on paper.

PAPER GUIDE
BENT-UP FLANGE
(PART OF BASE)

ADJUST FOR 0.10 TO 0.14 INCH GAP
BETWEEN PAPER GUIDE AND BENT-UP
FLANGE (FLANGE IS PART OF BASE)
MA-2595

Figure 7-3

Paper Guide Adjustment

7-4

7.4 PAPER OUT SWITCH ADJUSTMENT
This procedure describes paper out switch adjustment.

Set power switch to OFF.

Lift up and remove printer cover. Make sure there is paper in LA120.

Loosen the two (4-40) screws at paper out switch (Figure 7-4).

ARM TO BE FLUSH /
AT THIS POINT
AT 2ND TRANSFER

MA-2596

Figure 7-4

Paper Out Switch Adjustment

NOTE
If screws cannot be .loosened, it may be necessary to
reform switch arm to attain the adjustment.
4.

Rotate paper out switch counterclockwise until switch clicks (transfers), then rotate switch
clockwise until switch clicks again (transfers back). Tighten the two (4-40) screws to 5 ± I
in/lb.

Replace printer cover.

Restore power.

7-5

7.5 RIBBON TENSION ADJUSTMENT
The following procedure first checks individual spool drag; then, with ribbon installed, a carriage drag
test is performed.

Set power switch to OFF.

Lift up and remove printer cover.

Remove ribbon spools and ribbon.

Place an empty spool on side not b~ing driven.

Wind a small piece of string or ribbon on empty spool. Measure force required to pull string
in ~he direction the ribbon normally takes (Figure 7-5). The measured force should be approximately 0.14 to 0.20 kg (5 to 7 oz).

Adjust spool drag by tightening or loosening adjustment screw, while holding nut at base of
screw. An 11/32-inch wrench is required to hold nut.

Move direction changing guide and check remaining un driven spool for 0.14 to 0.20 kg (5 to
. 7 oz) tension.
PULL
5 TO 70Z
NOTE:
PERFORM THIS TEST
ONE SIDE AT A TIME
ADJUSTMENT
SCREW

DIRECTION
CHANGING
GUIDE
MA-2597

Figure 7-5

Ribbon Spool Tension Adjustment

7-6

(

NOTE
If a tension gauge is not available, ribbon tension can
be approximately adjusted by tightening adjustment
screw all the way (until compression spring under
ribbon chassis is completely compressed) and then
backing off 2-1/2 turns. (Each one-half turn of the
screw equals approximately 1 oz of tension.)

Install ribbon and spools.

With ribbon fully wound on left spool, the ribbon moving right to left across the face of the
print head, and the ribbon grommet starting to pull the reverse sensor to the right, a pull test
on the carriage from the left to right should indicate a pull of no more than 1.8 kg (4 lb)
(Figure 7-6). The ribbon should be moving right to left across the face of the print head
when the pull test is made.

PRINTHEAD

RIBBON
IDLER

RIBBON
SPOOL

RIBBON
. IDLER

RIBBON
SPOOL

RIBBON
IDLER

MA-2603

Figure 7-6

Ribbon Threading/Drag Test

7-7

Failure to achieve a pull of 1.8 kg (4 lb) maximum could indicate a problem in one of the
following areas:
•
•
•
•
•

Ribbon path
Carriage assembly (misaligned or damaged bearings)
Printer assembly (damaged end plates)
Ribbon chassis
Ribbon drive assembly

10.

Reinstall printer cover.

11.

Restore power.

7.6 RIBBON DRIVE ASSEMBLY ADJUSTMENT
This procedure describes the ribbon drive assembly adjustment.
1.

Set power switch to OFF.

Lift up and remove printer cover.

Rotate ribbon drive pulley on ribbon drive until clutch eccentric is at its highest point.

The ribbon drive pushrod should be at the center of the elongated hole (Figure 7-7). Rotate
ribbon drive pulley and check travel of pushrod to either side of the elongated hole. Travel
should be equal on both sides of the centerline.

To adjust for conditions listed in the previous step, loosen the 8-32 upper pivot screw (Figure 7-7) and move ribbon drive assembly the required amount (Figure 7-8).

Tighten the 8-32 screw to 18 ± 2 in/lb, and rotate ribbon drive pulley on ribbon drive until
clutch eccentric is at its highest point. Repeat Step 4.

Replace printer cover.

Restore power to LA120.

7-8

PIVOT
TAB

RIBBON DRIVE
PUSHROD
CENTERLINE OF
ELONGATED HOLE
o

I
®!=====§I

RIBBON
DRIVE
PULLEY
NOTE:
TRAVEL OF PUSH ROD TO BE EQUAL ON BOTH
SIDES OF THE ELONGATED HOLE.
MA-2598

Figure 7-7

Ribbon Drive Adjustment

7-9

PUSH ROD
RETAINING RING

RAISED PORTION
OF PIVOT TAB

COMPRESSION
SPRING

FLAT WASHER

RIB ON
ECCENTRIC TAB
MA-2573

Figure 7-8

Ribbon Drive Assembly

(
7-10

7.7 IDLER GEAR ASSEMBLY ADJUSTMENT
This procedure adjusts the idler gear assembly for the correct amount of backlash.
1.

Set power switch to OFF.

Perform printer housing removal procedure (Paragraph 6.2.1).
NOTE
Idler gear backlash can be checked by going directly
to Step 4.

To adjust backlash loosen the two (8-32) screws securing idler gear assembly to side plate
(Figure 7-9).

IDLER GEAR
ASSEMBLY

LINE FEED
KNOB

6-32
SCREW

0.002 - 0.007 IN.
BACKLASH AND EQUAL
DEPTH PENETRATION
LEFT-HAND
SIDE PLATE
MA·2599

Figure 7-9

Idler Gear Assembly

7-11

With idler gear in mesh with stepping motor gear and tractor drive gear, adjust idler gear to
achieve equal depth penetration and a backlash* of 0.0508 to 0.01778 mm (0.002 to 0.007 in)
between each pair of gears (Figure 7-9). The idler gear should be free to slide in and out.
Rotate gears to check backlash in several places.

Tighten the two (8-32) screws to 18 ± 2 in/lb of torque.

Perform printer housing installation procedure (Paragraph 6.2.2).

Restore power to LA 120.

7.8 BUMPER ASSEMBLY ADJUSTMENT
Tighten the screws (Figure 7-10) until the top of the washers are 43.69 mm (1.72 in) from the right and
left side plates. Center the spring around the screw.

1.72 in.

(43.69mm)

(43.69mm)
MA·2600

Figure 7-10

Bumper Assembly Adjustment

*Backlash is the amount a gear turns prior to turning the gear it meshes with.

7-12

7.9

PRINT BAR ADJUSTMENT
1.

Remove power from LA120.

Remove printer housing (Paragraph 6.2.1).

Remove ribbon and ribbon spools.

Check print bar adjustment by moving print head along carriage shafts, with carriage lever
in maximum forward position, and checking distance from print head jewel to print bar. As
the print head moves from one end of the carriage shafts to the other, the distance must be
0.010 ± 0.002 in. (See Figure 7-11 for measurement points.) If adjustment is not correct,
continue with procedure.

Position tractors in center of their travel.

Position print head to extreme right of carriage shafts.

Loosen the 7/16 inch hex-head screws on each end of the print bar.

With carriage lever in maximum forward position, use a feeler gauge to set print bar 0.010
inch from print head jewel as shown in Figure 7-11. Tighten down the 7/16 inch hex-head
screw on the right end of the print bar.
NOTE
Tightening the screw may move the print bar. In this
case, proceed to . Step 9 to adjust the left end of the
bar and then repeat Step 8.

Move the print head away from the print bar with the carriage lever and position the print
head to the extreme left of the carriage shafts. Move the print head to the maximum forward
position and perform Step 8 for the left end of the print bar.

10.

With carriage lever in maximum forward position, move print head from one end of the
carriage shafts to the other, while checking that space between print head jewel and print bar
does not vary more than ± 0.002 inch (i.e., at no point in the travel should a 0.013 inch shim
fit between the jewel and the print bar, nor should a 0.007 inch shim fail to fit between the
jewel and the bar). If the space varies more than ± 0.002 inch, the carriage shafts are probably bent and should be replaced (Paragraphs 6.7 and 6.9).

11.

Replace ribbon and ribbon spools.

12.

Replace printer housing (Paragraph 6.2.2).

7-13

""---PRINT HEAD

PRINTING FACE

o
7/16" HEX SCREWS (2)

PRINT BAR
A. TOP VIEW

END OF
PRINTRODS

JEWEL

TAPE GUIDE PROTRUSION (4)

B. FACE OF PRINT HEAD

NOTE:

INSERT FEELER GUAGE BETWEEN TAPE GUIDE PROTRUSIONS
AND UP AGAINST JEWEL.
MA·4678

(
\

Figure 7-11

Print Bar Adjustment

7-14

7.10 LUBRICATION
The LA120 DECwriter is factory lubricated; however, after an extended period of time, lubrication
may be required (oiling should be done infrequently). Table 7-1 lists those areas that may require
lubrication.
Table 7-1

Lubrication Points

Area

Lubricant

Amount

Carriage Shafts
(Figure 7-12)

Digital Part No. 49-00174, or
N ye Oil No. 622-00

1 or 2 drops on each carriage shaft

Ribbon Drive Assembly
(Figure 7-13)

SAE 30

1 or 2 drops on each of the five
places shown in Figure 7-13

ONE OR TWO DROPS
OF OIL (DEC PART NO.
49-001174, OR NYE 01 L,
NO. 622-00)
MA·2601

Figure 7-12

Carriage Shaft Lubrication

7-15

LEFT-HAND
SIDE PLATE -~- __._~

OIL CLUTCH

Figure 7-13 Ribbon Drive Assembly Lubrication

(
7-16

CHAPTER 8
20 rnA LA12X-AL OPTION

8.1 GENERAL
The 20 rnA loop option allows the terminal to communicate directly with the computer up to a distance of 305 m (1000 ft) without the use of a modem.
8.2 INSTALLATION
Table 8-1 lists the items in the 20 rnA LAI2X-AL option kit.

Table 8-1

20 mA LA12X-AL Option Kit

Item
No.

Quantity

Description

Part No.

20 rnA External interface cable

BC05F

20 rnA Assembly (logic board)

AO-7016059-0-0

20 rnA Harness assembly

AD-70 16186-0-0

Screw, hex head slotted
#8-32, 0.38 long

9009988-08

Washer, lock, ext. tooth #8

9008072-00

Install the 20 rnA option as described in the following steps. Refer to Figure 8-1 during the procedure.
Callout reference numbers in the figure are keyed to the item numbers in Table 8-1.
1.

Set TRANS switch on 20 rnA assembly to NORMAL. If the LA120 must provide current to
the transmit line, set switch to ACT.

Set REC switch to NORMAL. If LA120 must provide current on the receive line, set the
switch to ACT.

Lower rear cabinet door on LA120.

Disconnect and remove any plug connected to J8 on logic/power board.

Slip 20 rnA assembly (2) up through hole in floor of cabinet. Secure with two hex-head
screws (4) and washers (5).
8-1

S1
TRANS

rw:::rw

lQJMALlQJ

PINNING
FROM

P1-2
P1-3
P1-5
P1-7

P2-3
P2-2
P2-7
P2-5
MA-2320

Figure 8-1 . Installation of 20 rnA LA12X-AL Option
8-2

Connect 20 rnA harness assembly (3) between jack on 20 rnA logic board (2) and J8 on
logic/power board.

Place LAl20 in SET-UP mode. Select and store the following features:
Modem = I (FDX, no modem)
Auto Disconnect = 0 (OFF)

Connect PI of20 rnA external interface cable to bottom connector on 20 rnA logic board.

8.3 TEST AFTER INSTALLATION
After the LAl20 is connected to the system, transmit and receive data to verify the installation.

8.4
8.4.1

ELECTRICAL CHARACTERISTICS
Transmitter

Open circuit voltage
Voltage drop marking
Spacing current
Marking current

Min

Max

5.0V
20 rnA

50V
4.0V
2.0mA
50mA

Min

Max

15mA

2.5 V
3.0mA
50mA

8.4.2 Receiver

Voltage drop marking
Spacing current
Marking current

8.4.3

Pin Assignments (Figure 8-2)
I - Test Negative
2 - Transmit 3 - Receive5 - Transmit +
7 - Receive +
8 - Protective ground

900000000F

123

78
20m A CURRENT
LOOP CONNECTOR
MA3380

Figure 8-2

20 rnA Current Loop Connector

8-3

(

CHAPTER 9
EXPANDED BUFFER OPTION LA12X-DL

Typically a printer receives a series of characters, temporarily stores the characters in a buffer, and
then prints the characters one at a time. The LA120 contains a standard 1000 character buffer. The
expanded buffer option enables the standard 1000 character buffer to be increased in size to 4000
characters (4K).
An example of the use of this option is an LA120 connected to a video terminal (VT100) whose screen
contains 24 lines at 132 characters per line (a total of 3168 characters). The LA120 could receive these
characters at 9600 baud, store all 24 lines in the buffer, and then print the characters at the LA120
printing speed of 180 characters per second.
The LA120 buffer control feature* is not affected by this option. If XON, XOFF, and large buffer is
selected, XOFF will still be generated around 600 characters. The only difference is that the buffer is
now 4000 characters instead of 1000 characters.
If XON, XOFF, or the equivalent is not used, and the system is operating at high baud rates (for
example 2400 baud) for long periods, it may be possible to exceed the 4K buffer capacity.

*See LAl20 User Guide.

9-1

CHAPTER 10
LAI20-RE

10.1 INTRODUCTION
The LA120-RE is a receive only data communications terminal. Its 180 charjs printer uses an impact
dot matrix technique (7 X 9), and can handle data up to 9600 baud.
The LA120-RE is identical to the LA120 DECwriter III with one exception; the LA120-RE does not
have any type of keyboard.
The SET-UP parameters of this terminal are preset at the factory. Appendix B lists the factory stored
settings for each parameter. The legend strip label in Figure 11-5 shows how to interpret the settings.
Two options, the LA12X-HL full keyboard (Figure 10-1) or the LA 12X-YL function keypad (Figure
10-2), can be installed on the LA120-RE to allow customers to modify SET-UP parameters.
With the installation of the LA12X-HL option, the LA120-RE becomes a fully functioning LA120
DECwriter III. All features and capabilities of this combination are explained in previous chapters of
this manual.
When the LA12X-YL option is installed on the LA120-RE, it remains receive only; however, the SETUP parameters can now be changed to meet customer requirements. For a description of how to
operate the LA12X-YL function keypad option, refer to Chapter 12.
10.2 INSTALLATION
To install the LA120-RE, perform the procedures given in Chapter 2. Because the LA120-RE has no
keyboard, the self-test function cannot be performed. Sending data to the terminal will verify its
proper operation.

10-1

NUMERIC DISPLAY

'B' /'
SET-UP

ON LINE

flO

,-TAB,

CLEAR ALL

LOCAL ALTOC,ttAR

TOF

TOP -MAR- BOT

CTS

MAR

DSR

SETUP PAPEROUTl!

STATUS

STORE

BAUD

G:J
HERE
IS

LOCAL
FORM
FEED

r:lmrilriflrn~nml-lrnRE~LL ml-lr+l[]
DL!JL!J~

~L!Jl2JL!J

i i i

LINE
LOCAL

~LJL=J

LOCAL
LINE
FEED

BACK

IEJ'------BREAK'

SPACE

. ,G0000EJEJ0800ITJITJ E:roI
N

EJ@00000~00[!J~CJD~ETURN [I]
81 SHI~ 1000EJ000[J[JwG@J~

MA~15915

Figure 10-1

LAI2X-HL Keyboard

NUMERIC DISPLAY

[§J§]@]

LINE
LOCAL

RATE

SEL

LOC
FORM
FEED
LOC
LINE
FEED

LINE

B@J

CLR
ALL
TABS

DSR

PTR
NEW
LINE

TAB

o
o
o
o

TEST

SPACE

SET
UP
LOCK

PAPER OUT

SET UP

FORMS
LENGTH

B@9
MODEM

CHAN

STORE
RECALL

SET UP

S
T
A
T
U
S

MA-4511

Figure 10-2

LA12X-YL Keypad

10-3

CHAPTER 11
LAI2X-HL KEYBOARD OPTION

11.1 INTRODUCTION
The LAI2X-HL is a full keyboard kit for use with the LAI20-RE. When the LAI2X-HL is installed,
an LAI20-RE becomes a complete LA120 DECwriter III terminal.
11.2 INSTALLATION
Before installing the LA 12X-HL, examine the kit to determine that it contains all the items listed in
Table 11-1.
Table 11-1

LAI2X-HL Installation Kit

Description

Part Number

Quantity

Keyboard/Keycap Assembly
Keyboard Cable Assembly
Self-Tapping Screw
Plastic Cover
DECwriter III Label
Legend Strip Label

7015763-01
1700120-00
9010083-00
1215053-00
3615684-00
3615683-00

1
1
4
2
1
1

To install the LAI2X-HL on an LAI20-RE perform the following.
1.

Remove power by disconnecting ac plug.

Remove printer paper and printer cover.

Remove six (6-32) self-tapping screws and flat washers that secure printer housing to cabinet
base (Figure 11-1) and set them aside. Lift off printer housing and set aside.

Snap off cover from keyboard bezel.

Snap off keyboard bezel.

Open rear access door on cabinet.

Disconnect interlock/paper out cable from terminator in J 1 on logic board and remove
terminator card (Figure 11-2).

Route interlock/paper out cable up through cabinet and connect to J3 on keyboard. The
four-pin connector can be inserted in either direction.
11-1

2(6-32) SCREWS
(HIDDEN FROM VIEW)

1 (6-32)
SCREW

MA-4590

Figure 11-1

Printer Housing Removal and Installation

11-2

Dc:=J
J4

-J5

1 0000 10

5gggg ~~

_J6

_J3
POWER
SUPPLY

.J7

IJ9

J1 I

TERMINATOR
CARD
MA·4591

Figure 11-2 Terminator Card Removal

11-3

Route the end of the keyboard cable, with the notched connector, down through the cabinet
and connect it to J 1 on logic board. The notched end faces pin 1 on J 1 (Figure 11-3).

KEYBOARD
RIBBON CABLE

-J5
_J6

1 0000 10
2 0000 11
3 0000
12

LOGIC
BOARD

POWER
SUPPLY

.J7

IJ9

!~.

~~.,.,
~1J;1

MA-4592

Figure 11-3

Keyboard Cable Installation

11-4

10.

Connect the other end of the keyboard cable to J2 on the keyboard. The cable should enter
the left side of the connector when inserted in J2 (Figure 11-4).

NOTE
To prevent scratching or damaging keyboard or keyboard bezel, rest keyboard bezel on a piece of foam
or other cushioning material when performing the
next step.

KEYBOARD
(7015763)

TO
LOGIC

BOARD
MA-4589

Figure 11-4

Keyboard Installation

11.

Turn keyboard bezel upside down and secure keyboard with four (8-32) self-tapping screws
(Figure 11-4).

12.

Snap keyboard bezel into printer base.

13.

Snap two plastic covers into keyboard bezel on either side of keyboard.

11-5

14.

Attach legend strip and product designation labels to their appropriate space on keyboard
bezel (Figure 11-5).

REC
XMT
A
B
C
0
E
F
G
H
J
K
L
M
N
0
P
Q

R
S
U
V
W
X
Y

Z
I
T

Receive baud rate
Transmit baud rate
Auto-answerback O=Off
1=On
O=Small 1 = Large
Buffer control
Printer char. set
1=US
2=GB
Auto-disconnect
O=Off
1=On
Local echo
O=Off
1=On
Fonn length
Lines per fonn
Bell volume
1 =Hlgh
O=low
Horizontal pitch
Char. per Inch
Auto-newline
O=Off
1 =On
Key click
O=Off
1 =On
Auto-linefeed
O=Off
1=On
Modem/protocol
Keyboard char. set 1=US
2=GB
Alt. char. set
O=Off
1=On
Parity/data bits
HDX Initial state
O=XMT 1=REC
O=Off
1=On
Auto-repeat
1 = Yes
Secondary channel O=No
1 = Yes
O=No
Break enable
Lines per Inch
Vertical pitch
1 =None 2=LF 3=CR
Printer NL char.
O=No
1 = Yes
XON/XOFF
O=No
1 = Yes
Alt keypad mode
Auto-view
O=Off
1=On
Initialize to factory settings
Self test: Type a character to stop

~D~DD~D DECWRITER III

MA-4593

Figure 11-5

Label Installation

15.

Place printer housing on cabinet base and secure it with six (6-32) self-tapping screws and
flat washers.

16.

Install printer paper and cover.

17.

Restore power.

18.

Perform self-test procedure described in Chapter I, Part 2, of the LA 120 User Guide.

11.3 OPERATOR'S INFORMATION
Refer to Chapter I to operate the LAI20-RE with the LAI2X-HL option installed.

11-6

CHAPTER 12
LAI2X-YL OPTION

12.1 INTRODUCTION
The LAI2X-YL is a function keypad kit for use with the LAI20-RE. When the LAI2X-YL is installed,
the LAI20-RE remains receive only; however, the user now has the capability of modifying the SETUP parameters.
12.2 INSTALLATION
Before installing the LAI2X-YL, examine the installation kit to determine that it contains all the items
listed in Table 12-1.
Table 12-1

LAI2X-YL Installation Kit

Description

Part Number

Quantity

Keypad Assembly
Keyboard Cover Assembly
Keyboard Cable Assembly
Self-Tapping Screw
D ECwriter III Label

7016799-00
7016759-00
1700120-00
9010083-01
3615684-00

1
1
4

To install the LAI2X-YL on the LAI20-RE, perform the following.
1.

Remove power by disconnecting ac plug.

Remove printer paper and printer cover.

Remove six (6-32) self-tapping screws and flat washers that secure printer housing to cabinet
base (Figure 12-1) and set them aside. Lift off printer housing and set aside.

Snap off cover from keyboard bezel.

Snap off keyboard bezel.

Open rear access door on cabinet.

Disconnect interlock/paper out cable from terminator in J 1 on logic board and remove
terminator card (Figure 12-2).

Route interlock/paper out cable up through cabinet and connect to J2 on keypad. The fourpin connector can be inserted in either direction.
12-1

2(6-32) SCR EWS
(HIDDEN FROM VIEW)

1(6-32)
SCREW

2(6-32)
SCREWS

MA-4590

Figure 12-1

Printer Housing Removal and Installation

12-2

Dc::J
J4

-J5

1 0000 10

5gggg g

_J6
BlJ3
POWER
S.UPPLY

.J7

IJ9

J1 I

TERMINATOR
CARD
MA-4591

Figure 12-2 Terminator Card Removal

12-3

Route the end of the keyboard cable, with the notched connector, down through the cabinet
and connect it to J 1 on the logic board. The notched end faces pin 1 on J 1 (Figure 12-3).

10.

Connect the other end of the keyboard cable to Jl on keypad. The cable should enter the
bottom of the connector when inserted in J 1 (Figure 12-4).

KEYBOARD
RIBBON CABLE

-J5

1 0000 10
2 0000 11
3 0000 12

_J6

LOGIC
BOARD

POWER
SUPPLY

.J7

, :
J8

IJ9

MA-4592

Figure 12-3

Keyboard Cable Installation
12-4

(

,~
'"
'~

'" "
,"" ',I
'I

' I

A
J1~~3
8-32

.'".

TO
LOGIC

BOARD

SCREWS

FUNCTION

KEYPAD
(7016799)
MA-4588

Figure 12-4

Keypad Installation

NOTE
To prevent scratching or damaging the keypad or
keyboard bezel, rest the keyboard bezel on a piece of
foam or other cushioning material when performing
the next step.
11.

Turn keyboard bezel upside down and secure keypad with four (8-32) self-tapping screws
(Figure 12-4).

12.

Snap keyboard bezel into printer base.

13.

Snap keyboard cover assembly into keyboard bezel.

14.

Attach product designation label to appropriate space on keyboard bezel (Figure 12-4).

15.

Place printer housing on cabinet base and secure it with six (6-32) self-tapping screws and
flat washers.

12-5

16.

Install printer paper and cover.

17.

Restore power.

18.

Perform one of the two following self-test procedures given in Tables 12-2 and 12-3.
Table 12-2

Printing Self-Test

Procedure

Comments/Indication

Simultaneously press SET-UP LOCK and SETUP.

Locks printer in SET-UP mode. Set-up light
blinks.

Press SELF TEST.

Self-test pattern (Figure 12-5) will print out.

To stop test, press SELF TEST or any code producing character.

Exits from self-test. Pressing SET-UP will also
exit from SET-UP mode.

Table 12-3 Nonprinting Self-Test

Procedure

Comments /Indication

Remove keyboard cover assembly.

Allows access to printed circuit board.

Simultaneously press SET-UP LOCK and SETUP.

Locks printer in SET-UP mode.

Simultaneously press SHIFT and short the two
split lugs on the left side of the keypad circuit
board with a small screwdriver. Lugs are between 11 arid 12 and are marked > key.

Same as printing self-test except spaces are substituted for printing characters.

To stop test, press SELF TEST or any code producing character.

Exits from self-test. Pressing SET-UP will also
exit from SET-UP mode.

·,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\
'-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]
·./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]~

10123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]-_
'0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]~_\
)123456789:;<=>?@ABCDEFGHIJKLMNOpaRSTUVWXYZ[\]~_\a

,23456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\J~_\ab

!3456789:;<=>?@ABCDEFGHIJKLMNOpaRSTUVWXYZ[\J~_\abc
~456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]~_\abcd
l56789:;<=>?@ABCDEFGHIJKLMNOpaRSTUVWXYZ[\]~_\abcde
i6789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\J~~\abcdef
;789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]~_\abcdef~
MA-4695

Figure 12-5

Self-Test Printout

12-6

12.3 OPERATOR'S INFORMATION
This section describes the function of the indicator lights and control keys and describes how the
control keys are used.
12.3.1

Indicator Lights

NUMERIC Display
The numeric display indicates the current column number during normal operation. In SET-UP mode,
the numeric display may also indicate line number, baud rate, form length, etc.
LINE Light
The LINE light indicates the LA120 is on-line. Data is received only while on-line.
DSR Light
The DSR light indicates the modem is in data mode (data set ready).
PAPER OUT Light
The PAPER OUT light flashes to indicate the printer is not ready, due to one of the following conditions.
.
•
•
•

Paper out
Cover open
Print head jam

SET-UP Light
The SET-UP light flashes to indicate the LA120 is in SET-UP mode.
12.3.2

Control Keys

't~~~L
I
The LINE/LOCAL key switches the LA120 to or from line or local, as indicated by the LINE light.
IBAUDI
RATE
The BAUD RATE key selects the baud rate and number of stop bits.

ISELF
I
TEST
The SELF TEST key selects the printing self-test feature.

IpARI
SEL
The PAR SEL key selects the type of parity and the number of data bits.

ISHIFT
The SHIFT key, when pressed, causes the numeric display to indicate current line number. The SHIFT
key is also used during SET-UP mode as a control key.

,SET,
TAB
The SET TAB key sets a horizontal tab stop at the current column.

12-7

CLR
ALL
TABS
The CLR ALL TABS key clears all horizontal tabs.
LaC
FORM
FEED
The LaC FORM FEED key causes a form feed.
ISPACEI
The SPACE key generates code for a space.

PTR
NEW
LINE
The PTR NEW LINE key controls the selection of the printer's response to a received line feed or
carriage return.
LaC
LINE
FEED
The LaC LINE FEED key advances the paper one line at a time.
SET
UP
LOCK
The SET-UP LOCK key, when simultaneously pressed with the SET-UP key, locks the LA120 in SETUP mode.
IMODEMI
The MODEM key enables the selection of a communications protocol.

ISECl
IQLlliJ

The SEC CHAN key enables selection of a restraint mode for full duplex operation or indication of the
presence of a secondary channel for half duplex operation.
S
T
A
T
U
S
The STATUS key causes a message containing the currently selected values of the SET-UP parameters
to be printed.

(
12.. 8

ISET-Upi
The SET-UP key is used to examine or change the SET-UP parameters.
STORE
RECALL
The STORE RECALL key is pressed to recall the stored SET -UP parameters. When simultaneously
pressed with the SHIFT key, the current SET-UP parameters are stored.
12.3.3 SET-UP Mode
LA120 parameters can be changed only while in the SET-UP mode. Normally four steps are required
to perform SET-UP.
.
1.
2.
3.
4.

Enter SET-UP.
Change a parameter such as tabs, baud rate, etc.
Store the parameter if desired (see note).
Exit SET-UP.
NOTE
Storing enables the selected parameter to be stored
permanently. For detailed information, refer to the
storage, recall, and status description in the LA120
User Guide.

SET-UP should be performed with the LA120 in local mode.
Table 12-4 describes the two methods of entering and exiting SET-UP.
Table 12-4 Entering/Exiting SET-UP Mode
Method
No.

Procedure

Indication/ Comments

While holding SET-UP LOCK, press
SET-UP; release both keys. You may now
change any SET-UP feature.

SET-UP lamp flashes indicating you have
entered SET-UP.

Press SET-UP if you wish to exit SET-UP.

SET-UP lamp will stop flashing.

Press and hold SET-UP. You must continue to hold the SET-UP key while
changing any feature.

SET-UP lamp flashes indicating you are
in SET-UP.

Release SET-UP if you wish to exit SETUP.

SET-UP lamp will stop flashing.

12-9

12.3.4 Baud Rate (Speed)
Baud rate is the speed that data moves to the LA120. Due to the many systems the user must communicate with, a large selection of baud rates are available. Select the desired baud rate using the procedure in Table 12-5.

Table 12-5 Baud Rate Selection
Procedure

Indication/ Comments

Enter SET-UP mode.

SET-UP lamp flashes indicating you are in SETUP.

Press BAUD RATE.

Current selection of baud rate is displayed.

Continue pressing BAUD RATE to select receive baud rate as indicated by numeric display.

Baud
Rate
(Displayed)

Actual
Baud
Rate

Stop
Bits

50
75
110
134
150
200
300
600
1200
1800
2400
4800
7200
9600

50
75
110
134.5
150
200
300
600
1200
1800
2400
4800
7200
9600

2
2
2
1
1
1
1
1
1
1
1
1
1
1

12.3.5 Parity and Data Bits
Parity enables data errors to be monitored and thereby verifies the correctness of data. If an error in
transmission has occurred, the LA120 can detect it and indicate its presence by printing a special
symbol ( ~ ). In addition to parity, this feature enables the selection of 7 or 8 data bits. Select the parity
and data bits using the procedure in Table 12-6.

12-10

Table 12-6 Parity /Data Bits Selection
Procedure

Comments /Indication

Enter SET-UP mode.

SET-UP lamp flashes indicating you are in S~T
UP.

Press PAR SEL.

Current selection of parity bits is displayed in
numeric display.

Continue pressing PAR SEL to select parity and
data bits as indicated by numeric display.

Numeric
Display
Indicates

1
2
3
4

5
6
7
8

Parity
Receive

7
7
7
7
7
7
7

Ignore
Ignore
Ignore
Ignore
Odd
Even
None
None
Odd
Even

8
8
8

9
10
Exit SET-UP.

Data
Bits

SET-UP lamp will stop flashing.

12.3.6 Setting Form Length
The LAl20 measures form length in lines per form. To determine how long your form is, measure the
length of the form (Figure 12-6) in inches; then multiply the length of the form by the lines per inch in
memory. (Lines per inch is factory set at six.)
Form Length = Length of Form in Inches X Number of Lines per Inch in Memory.

PERFORATION
0

FORM
LENGTH

PERFORATION

MA-4594

Figure 12-6

Form Length

12-11

Use the procedure in Table 12-7 to enter the number of lines per form. Your choices of form length
range from 1 to 168 lines.
NOTE
Changing form length clears top and bottom margins, and sets the current line number to 1.
Table 12-7 Form Length Selection
Procedure

Indication / Comments

Enter SET-UP mode.

SET-UP lamp flashes indicating that you are in
SET-UP.

Press FORMS LENGTH.

Current form length in lines is displayed by numeric display.

Repeat pressing FORMS LENGTH to change
form length.

Numeric display will indicate a new value each
time FORMS LENGTH is pressed. Stop when
desired number of lines is displayed.

Exit SET-UP.

SET-UP lamp will stop flashing.

12.3.7 Printer New Line Character
.
This feature controls the way the LA 120 responds to the received line feed or carriage return cooe.
Three different responses can be selected as described in Table "12-8.
Table 12-8
Selections
Indicated
by Numeric
Display

Carriage Return/Line Feed Responses

Received Carriage
Return Code

Received
Line Feed Code

LA120 performs a carriage return.

LAI20 performs a line feed.

LA 120 performs a carriage return.

LA 120 performs a carriage return and
line feed.

LA120 performs a carriage return and
line feed.

LAI20 performs a line feed.

NOTE
In choice 2, the LA120 also performs a carriage return when it receives vertical tab and form feed characters.
The procedure for selecting the desired response is given in Table 12-9.
12-12

Table 12-9

Selection of Carriage Return/Line Feed Responses

Procedure

Comments /Indications

Enter SET-UP mode.

SET-UP lamp flashes indicating you are in SETUP.

Press PTR NEW LINE.

Current selection of printer new line character is
displayed in numeric display.

Continue pressing PTR NEW LINE.

Numeric display indicates one of the following:

(Table 12-8)

SET-UP lamp will stop flashing.

Exit SET-UP.

12.3.8 Modem
This feature enables the selection of a protocol that matches the communication requirements (see
Communications Chapter in LAl20 User Guide). Refer to Paragraph 12.3.9 (Secondary Channel) for
related modem SET-UPS. Selectable protocols are listed below.
1.
2.
3.
4.
5.

FDX (Full Duplex), No Modem
FDX, Modem
HDX (Half Duplex), Supervisory
HDX, EOT
HDX, EXT

Table 12-10 gives the procedure for modem selection.
Table 12-10

Modem Selection

Procedure

Comments /Indications

Enter SET-UP mode.

SET -UP lamp flashes indicating you are in SETUP.

Press MODEM.

Current selection of modem is displayed in numeric display.

Continue pressing MODEM to change numeric
display.

Numeric
Display
Indicates

Description

1
2
3
4
5

FDX, No Modem
FDX,Modem
HDX, Supervisory
HDX,EOT
HDX,ETX

Exit SET-UP.

SET-UP lamp will stop flashing.

12..;13

12.3.9 Secondary Channel
This feature has two meanings. First, if modem choices 1 or 2 (full duplex) have been selected, the
secondary channel feature can be used to indicate the restraint mode. The second meaning applies
when half-duplex modem choices 4 or 5 have been selected. With this choice, the secondary channel
feature can be used to indicate the presence of a secondary (reverse) channel. Table 12-11 gives the
procedure for secondary channel selection.
Table 12-11

Secondary Channel Selection

Procedure

Comments /Indications

Enter SET-UP mode.

SET-UP lamp flashes indicating you are in SETUP.

Press SEC CHAN.

Current selection of secondary channel is displayed in numeric display.

Continue pressing SEC CHAN.

Numeric
Display
Indicates

Exit SET-UP.

Selected

Modem
4or5
Selected

Speed
Control Mode

Secondary
Channel-No

Restraint
Mode

Secondary
ChannelYes

Modem

lor2

SET-UP lamp will stop flashing.

12-14

12.3.10 Status
A special feature of the LA120 is a printout of all the current SET-UP values except tabs and margins.
The following is a sample printout of a typical status message using the factory parameters.
REC

1200
1200

XMT

A
B
C
D
E
F
G
H
J
K
L
M
N

1
1
1

o
66
1
10
1

o
o
1
1
1
1

o
P

R
S
U

1
1

V
W

1
1

X
Y
Z

o
1

Refer to the legend strip label in Figure 11-5 for interpretation of codes.
NOTE
Do not press SHIFT when printing out status message.
To obtain a status printout, follow the procedure in Table 12-12.
Table 12-12 Status Printout Procedure
Procedure

Indication/Comments

Enter SET-UP mode.

SET-UP light will flash when LA120 is
in SET-UP.

Press STATUS.

Status message will be printed out.

Exit SET-UP.

SET UP light will stop flashing.

12-15

12.3.11 Store/Recall
Normally, setting up the LA120 is a one-time job. This is due to a unique feature that stores all the
settings in a permanent memory. Thus, the LA120 can be turned off without losing the following
settings:
A uto new line
Key click
Auto line feed
Modem
Keyboard and printer character set
HDX initial calling state
Auto repeat
Secondary channel
XON/XOFF
Alternate keypad mode
Auto view
Printer new line character
Alternate character set
Break action

Horizontal tab stop
Vertical tab stops
Left margin
Right margin
Top margin
Bottom margin
Line/local status
Baud rate
Answerback
Buffer control
Printer character set
A uto disconnect
Local echo
Form length
Horizontal Pitch

When the LA120 is turned on it will automatically enter the last settings stored by the operator.

NOTE
Setups must be stored to be saved.
Tables 12-13 and 12-14 contain the procedures for respectively storing and recalling LAl20 settings.
Table 12-13 LA120 Store Procedure
Procedure

Comments /Indication

Enter SET-UP mode.

SET UP light will start flashing indicating you
are in SET-UP.

Press and hold SHIFT and press STORE RECALL.

All" settings in the operating memory are stored
in nondestructive memory. Numeric display will
go blank for a few seconds.

Exit SET-UP.

SET-UP lamp will stop flashing.
Table 12-14 LA120 Recall Procedure

Procedure

Comments/Indication

Enter SET-UP mode.

SET UP light will start flashing
indicating you are in SET-UP.

Press STO RE RECALL~

Settings stored in permanent memory
will be recalled. Numeric display will
go blank for a few seconds.
SET-UP lamp will stop flashing.

Exit SET-UP.
12-16

(

APPENDIX A
LA120 OPERATOR REFERENCE CARD

DECWRITER III
LA120 OPERATOR
REFERENCE CARD
SET·UP
KEY

FUNCTION/COMMENTS

I CTRL I and I SET-UP I Locks LA 120 in set-up mode; SET-UP light flashes.
To exit set-up mode press I SET-UP I
Places LA 120 in set-up mode while ISET-Upi is
held down; SET-UP light flashes.
To exit set-up mode release I SET-UP I
NOTES:
1. LA 120 must be in set-up mode to set the following features.
2.

00 not use ! SHIFT I unless specified.

FORMS
FU N CTION/COMM ENTS

KEY

Display current line number

ISHIFT I

Releasing I SHIFTI returns display to currant
column number

m
ISHIFT! and

m
ISHIFTI and

Set horizontal tab at current column

m
m

IT!
ISHIFTI and

IT!

ffi)

(f]

Establish top of form (TO F)
Set minimum column number lIeft margin)
Set minimum line number (top margin)

III

Set maximum line number (bottom margin)

IT!

Clear top and bottom margins

Set maximum column number (right margin)

IT!
ISHIFT! and

Clear all vertical tabs

rnJ

III
ISHIFTI and

Clear vertical tab at current line
Clear all horizontal tabs

[i] od SHIFT! and 0
ISHIFT! and

Set vertical tab at current line
Clear horizontal tab at current column

Clear left and right margins

Form Length
NOTE: Changing form length clears top and
bottom margins and establishes TOF.
DISPLAY
1
th ru} Lines per form
168

A-I

FORMS (CONT)
FU NCTION/COMM ENTS

KEY

lEI

Horizontal pitch (Characters per inch)
NOTE: Changing horizontal pitch clears left and right margins.

5
6

5.00 CPI
6.00 CPI
6.60 CPI

7
8
10
12
13
16

8.25 CPI
10.0CPI
12.0CPI
13.2 CPI
16.5 CPI

Vertical pitch (Lines per inch)
NOTE: Changing vertical pitch clears top and bottom margins.

2 LPI
3 LPI
4 LPI
6 LPI

3
4
6

8
12

8 LPI
12 LPI

OPERATOR COMFORT
KEY

FUNCTION/COMMENTS

Bell volume
o = Low Volume
1 = High Volume

[K]

Key click
0= Off
1 = On

lliJ

Auto repeat
0= Off
1 = On
Last character view

o = Manual
1 = Auto

COMMUNICATION
KEY

FUNCTION/COMMENTS
Auto answerback
0= Off

1 = On
Buffer control

o = Small
1 = Large
Printer character set
1
United States
United Kingdom
2

=
=

Auto disconnect
0= Off

= On

Local echo
0= Off

= On

(
A-2

COMMUNICATION (CO NT)
KEY

FUNCTION/COMMENTS

Auto new line at right margin
0= Off
1 = On
Auto line feed (Return key)
0= Off
1 = On
Modem

1 = FOX. No Modem
2 = FOX. Modem
3 = HDX. Supervisory
4 = HDX. EOT

5 = HDX. ETX
Keyboard and printer character set
1 = United States

2 = United Kingdom

@] (letter)

Alternate character set
0= OFF

1 = ON
Parity and data bits
PARITY

DATA
DISPLAY

BITS

REC

XMT

IGNORE
IGNORE

MARK

2
3
4
5
6
7

7
7
7
7
7
7
7

IGNORE

000

B
B

9
10

SPACE

IGNORE

EVEN

ODD

000

EVEN

NONE

NONE
ODD
EVEN

000

NONE
EVEN

HDX initial calling state
0= Transmit
1 = Receive
Secondary channel
FOX •
MODE

HDX •
REV.CH.

Speed
Restraint

"Nil

DISPLAY

-0--

• See M Key. Modem
Break enabled

o = No
1 = Yes
Printer new I ine character
1 = None

2 = Line feed (LF)
3 Return (CR)

XONIXOFF
0= No
1

= Yes

Alternate keypad mode

0= No
1 = Yes

\,
)

A-3

Yes

COMMUNICATION (CONT)
FUNCTION/COMMENTS

KEY

@) (number)

Selects receive and transmit baud rates and number
of stop bits.
BAUD RATE
(DISPLAYED)

STOP BITS
---2

50
75
110
134
150

2
2

200
300
600
1200
1800
2400
4800
7200
9600

I SHIFT I and @)

Selects split baud rates:
@]selects receive baud rate;

I SHIFT I and @]

then offers a choice of three transmit baud rates.
RECEIVE
8AUD RATE
(NOT DISPLAYED)

TRANSMIT
BAUD RATE
(DISPLAYED)

TRANSMIT
STOP BITS

600

75
150
600

2
1
1

1200

75
150
1200

2400

300
600
2400

4800

(
'I

300
600
4800

STORE RECALL AND STATUS
FUNCTION/COMMENTS

KEY

(letter)

Select factory set-up parameters

[ID

Print status message

Recall set-up parameters

I SHIFT I and ~

Store set-up parameters

SELF TEST
KEY

m
I SHIFT I and ~

FUNCTION/COMMENTS
Initiate printing self test
Initiate non-printing self test
NOTE: Type any character in set-up mode to
stop self test.

PRINTED IN U.S.A. EK-LA120-RG-001

(
A-4

APPENDIX B
FACTORY PARAMETER SETTINGS

The initial settings of the LA120 parameters made at the factory prior to shipment are given below.
Parameter

Setting

Horizontal tab stops

1,9,17,25,33,41,49,57,65,73,81,89,97,105,113,121, 129, 137, 145, 153,
161, 169, 177, 185, 193, 201, 209, 217

Vertical tab stops

1,9,17,25,33,41,49,57,65,73,81,89,97,105,113,121, 129, 137, 145, 153,
161

Left margin
Right margin

132

Top margin
Bottom margin

Line/Local Status

On-line

REC
XMT
A

1200
1200

C
D
E
F
G

H
J
K
L

M
N

o
p

R
S
U
V

o
1
1
1

o
66
1
10
1

o
o
1
1
1
1

o
1

W
X
y

1
1

B-1

Reader's Comm'ents

LA120
TECHNICAL MANUAL
EK-LA 120-TM-001

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