Digital Equipment PDP-11/23-PLUS User guide

PDP-II/23-PLUS
SYSTEM MANUAL

EK-1T238-0P-001
PDP-ll/23-PLUS
SYSTEM MANUAL
Prepared by Educational Services
of
Digital Equipment Corporation

1st Edition, January 1982
Copyright ® 1982 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.
The manuscript for this book was created on a DIGITAL Word
Processing System and. via a translation program, was
automatically typeset on DIGITAL's DECset-8000 Typesetting
System.
Book production was done by Educational Services
Development and Publishing
in Marlboro. MA.
The following are trademarks of Digital Equipment Corporation:
DEC EduSystem RSTS
DECnet lAS RSX
DECUS MASSBUS TOPS-IO
DECsystem-IO MINC-II
TOPS-20
DECSYSTEM-20 OMNIBUS
UNIBUS
DECwriter
OS/8
VAX
DIBOL PDP VMS
mamaala
PDT VT

CONTENTS
PREFACE
CHAPTER 1 GETTING STARTED
INTRODUCTION................................................................................... 1
CONTROL PANEL ................................................................................ 2
SYSTEM CONFIGURATION .................................................................. 2
RL02 Disk Drives...................................................................... 2
BREAK Key............................................................................... 4
Receive SpeedITransmit Speed .............................................. 5
Bootstrap Technique ................................................................ 5
DISK CARTRIDGE LOADING PROCEDURE........................................... 5
INITIAL SYSTEM START-UP ................................................................. 7
LOADING THE OPERATING SySTEM.................................................... 7
CHANGING A DISK CARTRIDGE........................................................... 8
POWERING DOWN ............................................................................... 9
CHAPTER 2 PROGRAMMING
INTRODUCTION................................................................................... 11
DIAGNOSTIC PROGRAMS.................................................................... 11
The DLDP + Diagnostic Programs............................................ 12
How to Find a Diagnostic Program.................................... 12
Help Messages................................................................. 14
Diagnostic Chain Files...................................................... 14
Running Individual Diagnostic Programs........................... 14
How to Copy the Diagnostic Disk.............................................. 15
DEC/X11 .................................................................................. 17
RSX-11M SOFTWARE.......................................................................... 18
Monitor Functions..................................................................... 19
Multiprogramming............................................................. 19
Event-Driven Priority Scheduling....................................... 19
Task Checkpointing .......................................................... 19
Dynamic Memory Allocation.............................................. 19
Executive.......................................................................... 19
II 0 Services............................................................................. 20
File System .............................................................................. 20
User Interface........................................................................... 20
iii

iv CONTENTS
RSTS/ E AND CTS-500 SOFTWARE..................................................... 20
Timesharing.............................................................................. 21
Dynamic Allocation of System Resources................................ 21
Privilege................................................................................... 22
Batch Processing ..................................................................... 22
File System. ............................................................................. 22
Terminal Handling.....................................................................
23
Shared Common Code.............................................................. 24
Disk Data Cache....................................................................... 24
Intertask Communication.......................................................... 24
Disk File and Device Backup.................................................... 24
System Operation Control........................................................ 25
System Reliability and Maintenance......................................... 25
User Command languages...................................................... 26
DIGITAL Command language (DCl) ........................................ 26
Concise Command language................................................... 26
CHAPTER 3 INSTALLATION CHECKOUT AND TROUBLESHOOTING
INTRODUCTION................................................................................... 27
UNPACKING PROCEDURE ................................................................... 27
INSTAllATION CHECKOUT PROCEDURE............................................ 29
TROUBLESHOOTING............................................................................ 36
Using the Flowchart.................................................................. 39
BOOTSTRAP DIALOG RESPONSE........................................................ 39
AC Power Indications ............................................................... 40
874 Power Controller................................................................ 40
Terminal Off-line Checks ......................................................... 40
Terminal Power Cable Connection ............................................ 40
Computer Switches and Indicators........................................... 40
PWR OK Indicator..................................................................... 41
Check Power Switches and Power Cable................................. 41
RUN Indicator ON ..................................................................... 41
Terminal Interface Cabling ........................................................ 41
NO PROMPT AFTER BOOTSTRAP........................................................ 42
Disk Drive Power Indications.................................................... 42
Check Disk Cable Connections................................................ 42
Check Disk Cartridge...............................................................
43
CHAPTER 4 ADVANCED HARDWARE CHECKOUT
INTRODUCTION................................................................................... 45
BOOTSTRAP AND DIAGNOSTIC PROGRAMS....................................... 45
Diagnostic Errors...................................................................... 46
Serial Line Unit Error......................................................... 49
CPU, Memory, or ROM Error ............................................. 49
Disk Bootstrap Errors........................................................ 49
Trap Vector.......................................................................
51
ON-LINE DEBUGGING TECHNIQUE (ODT) ............................................ 51

CONTENTS v
TROUBLESHOOTING WITH DLDP+ ..................................................... 52
Error
Messages.. ...................................................................... 52
Restarting Programs................................................................ 52
Modifying a Diagnostic Program...............................................
52
Single Instruction Execution ..................................................... 54
Expanding the Diagnostic Chain............................................... 54
TROUBLESHOOTING WITH DECI X 11 .................................................. 56
Error Messages........................................................................ 56
The System Error Printout................................................. 56
The Data Error Printout ..................................................... 57
The Status Error Printout .................................................. 57
Selecting and Deselecting Program Modules ........................... 58
Expanding the Run-Time Exerciser........................................... 59
CHAPTER 5 SYSTEM COMPONENTS
INTRODUCTION................................................................................... 61
PDP-11 123-PLUS MODELS.................................................................. 61
PDP-11 123B PROCESSOR SUBSySTEM............................................. 61
KDF 11-B Microprocessor......................................................... 64
MSV 11-P Memory..................................................................... 68
DZV 11 Asynchronous Multiplexer............................................. 70
RL V12 Disk Controller.............................................................. 70
BA 11-S Mounting Box............................................................... 73
H9276 Backplane.............................................................. 73
H7861 Power Supply......................................................... 73
H403-B AC Input Box......................................................... 73
Control Panel.................................................................... 76
H349 DISTRIBUTION PANEL................................................................. 76
RL02 DISK SYSTEM............................................................................. 78
H9642 CONSOLE CABINET .................................................................. 79
874 POWER CONTROLLER................................................................. 79
CHAPTER 6 OPTIONAL SYSTEM COMPONENTS
INTRODUCTION ................................................................................... 81
TERMINAL OPTIONS............................................................................ 82
VT100 and VT102 Terminals .................................................... 82
Summary of VT1 00 and VT1 02 Specifications.......................... 83
LA 120 DECwriter III................................................................... 83
BA 11-S EXPANDER BOX ...................................................................... 85
CHAPTER 7 SYSTEM REQUIREMENTS
INTRODUCTION.
.................................................................................. 87
SYSTEM POWER. ................................................................................ 87
ENViRONMENT....................................................................................
88
Heat Dissipation....................................................................... 89
Radiated Emissions.................................................................. 89
Cleanliness............................................................................... 89
Cooling..................................................................................... 90

vi CONTENTS
Static Electricity....................................................................... 90
Disk Cartridge Storage............................................................. 90
CHAPTER 8 RULES FOR EXPANSION
INTRODUCTION................................................................................... 91
PRIORITY CHAINING............................................................................ 91
MULTIPLE BACKPLANE CONFIGURATION RULES.............................., 91
MICROPROCESSOR RECONFIGURATION ........................................... 94
CPU Option............................................................................... 94
Device Selection...................................................................... 96
Boot / Diagnostic ROM.. ............................................................ 97
Serial Line Units (SLU) .. ........................................................... 99
SLU Baud Rate Selection.................................................. 99
Character Formats ........................................................... 99
Break Halt......................................................................... 101
Internal/External SLU Clock Jumpers ...................................... 101
Test Jumpers ............................................................................ 102
MEMORY EXPANSION ......................................................................... 102
Configuring the MSV11-P ......................................................... 103
Starting
Address ............................................................... 105
Control and Status Register (CSR) Address ..................... 107
Power ............................................................................... 108
Bus Grant Continuity ......................................................... 108
General Jumpers.............................................................. 108
MASS STORAGE DISK EXPANSiON..................................................... 108
CABINET EXPANSION .......................................................................... 108
Removal
of Cabinet Side Panels............................................... 110
APPENDIX A RELATED DOCUMENTATION
APPENDIX B
PDP-ll 123-PLUS GLOSSARY

CONTENTS vii
FIGURES
1-1 PDP-11 /23-PLUS Computer System ........................................
1-2 Control Panel
Switches and Indicators..................................... 2
1-3 Installation
Checklist.. .............................................................. 3
1-4 RL02 Disk Drive (Front View).................................................... 4
1-5 Disk Cartridge Loading............................................................. 6
2-1 Program Code and Name......................................................... 12
2-2 DLDP+ Help
Message. ............................................................ 13
2-3 Example of a Directory Listing.................................................. 13
2-4 Example of a Diagnostic Chain................................................. 14
3-1 PDP-11 /23-PLUS System Unpacking Instructions.................... 28
3-2 Installation of Cabinet Legs and Stabilizer FooL..... ................. 29
3-3 PDP-11 /23-PLUS System (Rear Panel Removed)....................
30
3-4 RL02 Lower Disk Drive (Rear View).......................................... 31
3-5 874 Power Controller (Front View) ........................................... 32
3-6 PDP-11
/23B Subsystem (Rear View) ....................................... 33
3-7 PDP-11 /23-PLUS System Cable Connections.......................... 34
3-8 RL02 Head Positioner Restraining Bracket............................... 35
3-9 PDP-11 / 23-PLUS Control Panel Operation .............................. 37
3-10 PDP-11 / 23-PLUS Troubleshooting Flowchart .......................... 38
4-1 KDF 11-B Diagnostic LED Display............................................. 50
5-1 PDP-11 /23B Subsystem........................................................... 63
5-2 Basic PDP-11 /23-PLUS System's Module Location in
an H9276 Backplane.................................................................
64
5-3 KDF11-B Jumper, Switch, and Diagnostic
Display Locations..................................................................... 65
5-4 MSV11-P Memory Factory Jumper Locations........................... 71
5-5 DZV 11 Factory Jumper and Switch Locations .......................... 72
5-6 RLV12
Factory Jumper Locations ............................................ 74
5-7 BA11-S
Major Assemblies......................................................... 75
5-8 H9276
Connector and Jumper Locations.................................. 75
5-9 Control Panel Printed Circuit Board .......................................... 76
5-10 PDP-11 /23-PLUS Distribution Panel (H349) ............................. 77
6-1 Standard EIA Interface..............................................................
81
6-2 Telephone Line Interface Via Data Set ..................................... 81
6-3 VT100 Video Terminal.............................................................. 82
6-4 LA120 DECwriter 111...................................................................
84
7 -1 PDP-11 /23-PLUS Power Connectors....................................... 87
8-1 PDP-11 /23-PLUS System (H9276) Two Backplane
Configuration............................................................................ 92
8-2 PDP-11 /23-PLUS System Three Backplane Configuration .......
93
8-3 KDF 11-B Jumper, Switch, and Diagnostic Display
Locations................................................................................. 95
8-4 MSV11-P Jumper Locations..................................................... 104
8-5 CSR Bit Allocation.................................................................... 107
8-6 Left and Right Side Panel Removal........................................... 111

viii CONTENTS
TABLES
1-1 Control Panel Operation .. ......................................................... 3
1-2 Control Panel LED Indicators.................................................... 3
1-3 RL02 Front Panel Operation..................................................... 4
3-1 Voltage and Range
Selector Setting........................................ 31
3-2 System's Diagnostics............................................................... 36
4-1 Dialog Commands. ................................................................... 46
4-2
List of Error Halts...................................................................... 47
4-3 Diagnostic LED Error Display.................................................... 50
4-4 DEC / X11-DLDP+ Program Cross Reference........................... 58
5-1 PDP-11 /23-PLUS System Components.................................... 62
5-2 Factory Jumper Configuration .................................................. 66
5-3 Bootstrap/ Diagnostic
Factory Switch Configuration ................ 68
5-4 SLU Baud Rate Factory Switch Configuration........................... 68
5-5 MSV11-P Versions. .................................................................. 69
5-6 MSV11-P (M8067-LA and KA) Jumper Configuration................ 69
5-7 DZV11 (M7957) Jumper Configuration (Basic System)............. 72
5-8 DZV11 (M7957)
Factory Switch Setting ................................... 73
5-9 Control Panel Jumpers............................................................. 76
5-10 Distribution Panel Cable Assemblies to PDP-11 /23-PLUS
System Options.. ...................................................................... 78
7
-1 System Model Designations..................................................... 88
7-2 Optional Console Terminals ..................................................... 88
8-1 CPU Jumper Configuration....................................................... 94
8-2 On-Board Device Selection Jumpers........................................ 96
8-3 Diagnostic/Bootstrap Program Selection................................. 97
8-4
Diagnostic/Bootstrap Program Switch Position........................ 97
8-5 Bootstrap Program Selection....................................................
98
8-6 ROM-EPROM Jumpers............................................................. 98
8-7 Baud Rate Selection................................................................. 99
8-8 Character Format Jumpers....................................................... 100
8-9 Character Jumper Configuration............................................... 101
8-10 Break Halt Jumper Configuration.............................................. 102
8-11 Internal/External SLU Clock Jumper Configuration.................. 102
8-12 Manufacturing Test Jumpers .................................................... 103
8-13 Field Service Test Jumpers...................................................... 103
8-14 Starting Address Configuration ................................................ 106
8-15 CSR Address Selection............................................................ 108
8-16 General Jumpers...................................................................... 109
8-17 PDP-11 /23-PLUS Expansion Cabinets..................................... 109

PREFACE
This manual provides the user with information on the operation, con-
figuration, and maintenance for the PDP-11 /23-PLUS system. It describes
both
the hardware and software operating features of the system. The
configuration requirements are explained, and the factory configuration is
defined. The manual includes software
diagnostic programs used to trou-
bleshoot
the system and a hardware system checkout procedure.
NOTE: The dialog used by the operator when communicating with the
system is printed in orange.
Specifications for the optional terminals appear in Chapter 6. Chapter 8
presents the rules for expanding the system. All address references such
as registers, software locations, and interrupt vectors are octal numbers.
ix

INTRODUCTION
CHAPTER 1
GETTING STARTED
The PDP-11 /23-PLUS is a high performance microcomputer system used
for developing and executing programs for a variety of applications. Op-
tional hardware and software are available for applications such as high-
level language program development, foreground/background real-time
support, multiprogramming, and equipment monitoring and control.
The PDP-11 /23-PLUS (Figure 1-1) includes an operator's switch panel, a
processor with memory management functions, a 256K byte memory (ex-
pandable to 1 megabyte), a 2-channel serial line interface, and two RL02
disk drives. The memory supports the extended LSI-11 bus (22-bit ad-
dress). Each disk drive has a removable top-loading disk cartridge that
provides 10 million bytes of storage. Special bootstrap read-only memo-
ries (ROM) initiate the system software when the system is turned on and
can also automatically test the system.
MR-7400
Figure 1·1 PDp·11 /23-PLUS Computer System

2 GETTING STARTED
DIGITAL provides either an LA120 DECwriter III, VT100, or VT102 terminal
for the PDP-11 /23-PLUS system (see Chapter 6). The system terminal im-
plements communication between the user and the processor. Interface
with the system and the user's terminal is provided by a patch and filter
panel located at the rear of the system's cabinet. Chapter 5 contains a
complete description of the PDP-11 /23-PLUS.
CONTROL PANEL
Control panel switches provide power, stop, and bootstrap commu-
nications between the user and the microcomputer system. This panel
contains three switches: AUX ON/OFF, HALT, and RESTART. Switch lo-
cations are shown in Figure 1-2, and their operation is listed in Table 1-1.
LED
INDICATORS
PWR OK RUN
CONTROL
SWITCHES
ON
RESTART HALT AUX OFF
Figure 1-2 Control Panel Switches and Indicators
MR-2026
The switch panel contains three LED indicators, but only two are used:
POWER OK and RUN. Their operation is listed in Table 1-2.
SYSTEM CONFIGURATION
The PDP-11 /23-PLUS is configured and tested at the factory and is ready
to be installed at the user's site. Several features can be changed when
the system is installed by DIGITAL's Field Service. Figure 1-3 is a check-
list to use as a reminder of the desired configuration when the system is
installed.
RL02 Disk Drives
The RL02 disk drive is a random-access, mass storage device with a re-
movable, top-loading disk cartridge. A cover lifts up to gain access to the
disk. The RL02 has four indicators on its front panel, as shown in Figure
1-4. Their
operation is listed in Table 1-3.

GETTING STARTED 3
Table 1-1 Control Panel Operation
Switch
AUX
ON /OFF
HALT
RESTART
Position
OFF
ON
Up (Enable)
Down (Halt)
RESTART
(momentary
switch)
Function
In the ·normal factory configuration, setting this switch to off
turns off the system ac power .
In the normal factory configuration, setting this switch to on
turns on the system ac power. If the HALT switch is also up,
the system automatically boots at this time.
Placing this switch up enables the processor to run.
The
processor halts and responds to console ODT com-
mands. Refer to the Microcomputer and Memories Hand-
book for ODT instructions.
When the Halt switch is up, the processor car.ries out a
power-up sequence and displays the bootstrap dialog as
below .
TESTING MEMORY
0256 .KW MEMORY
START? DLO<CR>
Table 1-2 Control Panel LED Indicators
LED
Function
PWR OK This LED is on when the processor is generating correct dc output voltages .
RUN This LED
is on when the processor is operating; the LED goes off when the
processor is not executing instructions.
NOTE: It is possible that this indicator may blink . It should be ignored when the OOT
character is enabled .
OPTIONAL FEATURE
CHECK DESIRED CONFIGURATION
UNIT O/ UNIT 1 TOP: 0
UNIT 1 0
UNIT 0
BOTTOM: UNITO
UNIT 1
BREAK KEY FUNCTION
0 DISABLED 0
HALT
SYSTEM
RECEIVE SPEED 0
9600 BAUD
0 CHANGE TO: -
(AS SHIPPEDI
TRANSMITSPEED
0 9600
BAUD
0 CHANGE
TO:-
(AS SHIPPEDI
BOOTSTRAP
TECHNIQUE
0
DIALOG USING 0
AUTOMATIC
DLO OR DLl
-TRANSMIT AND RECEIVE SPEED MUST MATCH TERMINAL
MR · 7362
Figure 1-3 Installation Checklist

4 GETTING STARTED
LOAD
(RUN/STOP)
READY
(UNIT SELECT)
WRITE
PROT
Figure 1-4 RL02 Disk Drive (Front View)
Table 1-3 RL02 Front Panel Operation
Indicator
LOAD
(push-button)
UNIT SELECT
(READY)
FAULT
WRITE PROT
(push-button)
BREAK Key
FuncUon
Lights to indicate that the spindle has stopped and a cartridge can be
loaded.
Lights
to indicate thatdrive 0 or '1 is ready to read, write, or receive
controller commands.
Lights
to indicate, that a drive error condition exists.
Lights
to indicate that the cartridge currently mounted is protected
from having
data written onU.
The BREAK key is factory configured to halt the system. For the conven-
ience of the operator, who must be aware of its function, the BREAK key
can be disabled so that it is ignored when typed. The key is normally lo-
cated near the RETURN key. If the BREAK key is set to halt and is acci-
dentally typed, it could halt the system in the middle of a program. To
change the configuration, refer to the terminal's user guide (listed in Ap-
pendix A).

GETTING STARTED 5
Receive Speed/Transmit Speed
The receive and transmit speeds are factory configured to 9600 baud.
This is the normal speed for the VT100, VT 102, and LA120 DECwriter ter-
minals. To change the baud rates refer to the terminal's user guide (listed
in Appendix A).
Bootstrap Technique
The user can select either an automatic boot or an operator-controlled
boot. To use either boot, the HALT switch must be set to ENABLE and the
AUX ON /OFF switch turned ON. The operator-controlled boot requires the
operator to indicate which bootable disk drive, DLO or DL 1, has been se-
lected.
DISK CARTRIDGE LOADING PROCEDURE
Use the following procedure to load a disk cartridge (Figure 1-5).
1. Turn the power on with the AUX ON / OFF switch (Figure 1-2). After
15
seconds, the LOAD indicator on each drive should light.
NOTE: A safety interlock prevents the opening of the RL02 cartridge ac-
cess door when no power is available to the drive. Check that the RL02
head restraining bracket is in its proper position, as shown in Figure 3-8.
2.
Raise the cartridge access door, as shown in Figure 1-5.
3.
Support cartridge (A) with left hand.
4. Push
handle slide (C) to left with thumb of right hand.
5.
Raise cover handle (D) to full upright position, releasing protection
cover (B).
6. Lift
cartridge (A) from protection cover (B) and carefully seat it on
drive
spindle with the handle recess facing the rear of the drive.
7. Carefully
rotate top cover handle (D) a few degrees clockwise and
counterclockwise to ensure that it seats firmly.
8. Gently lower the top cover handle (D) to the horizontal position to
engage the cartridge on the drive spindle.
9. Place protection cover (8) on top of the cartridge.
10. Close the cartridge access door.

6 GETTING Sl AR1ED
11. Press the LOAD indicator button. Note that the LOAD indicator goes
out; and, after 30 seconds, the unit-select (READY) indicator illumi-
nates.
12. If write protection is desired, press the WRITE PROT indicator button.
COVER HANDLE D
PROTECTION COVER CARTRIDGE
MR·1862
Figure 1·5 Disk Cartridge Loading

GETTING 8T ARTED 7
INITIAL SYSTEM START-UP
The recommended system start-up sequence is listed below. If the system
does not respond as noted, refer to Chapter 4 for further instructions.
1. Check that your terminal is configured as follows.
a. Power ON/OFF switch is set to ON.
b. LINE / LOCAL mode is set to LINE.
c. FOX/ HDX is
set to FOX (full-duplex).
d. BAUD RATE matches the system.
2. Set switches on the PDP-11 /23-PLUS control panel as follows.
a. Set the HALT switch up (enable).
b.
Set the AUX ON / OFF switch to ON. In approximately 15 seconds,
the PWR OK and LOAD indicators will light.
NOTE: The FAULT indicator may also light at this time. It should go off,
however,
as soon as the disk drive is accessed. If it does not go off, con-
sult Figure 3-10, the PDP-11123-PLUS Troubleshooting Flowchart, or your
local DIGITAL Field Service office.
3. Ensure that the system software disk cartridge is READY and write
protected. Press the WRITE PROT indicator button on the RL02 if it is
not illuminated.
NOTE: Operating systems normally require that the system disk be write
enabled; however, do not enable it until the master cartridge has been
copied.
LOADING THE OPERATING SYSTEM
Before the computer can read the programs on the disk cartridge, the disk
drive must be bootstrapped. The bootstrap is a short program that estab-
lishes a communication path between the computer and the disk drive.
Once the bootstrap program has been executed, the computer can inter-
act with the disk drive to use the operating system programs contained
on the disk. To boot disk drive 0 (usually the upper disk), proceed as fol-
lows.
NOTE: In this manual, examples of commands that are typed by the op-
erator are printed in orange. Characters that are printed or displayed by
the computer appear in black type.
Characters enclosed by < > brackets are nonprinting commands. For
example, <CR> indicates carriage return, and the operator should press
the RETURN key.

8 GETTING STARTED
When the AUX ON / OFF switch is turned ON (after a halt, press the RE-
START switch momentarily), the computer prints the following on the ter-
minal. (If a
video terminal is used, allow a short warm-up period until the
cursor appears on the screen.)
TESTING MEMORY
0256.KW
START?
The bootstrap and diagnostic software program automatically sizes the
available memory in
the system. The actual available memory maximum is
1 megabyte. The
user should be aware of the actual memory and not de-
pend on the printout. If the displayed memory size does not agree with the
actual memory size in the system, a hardware problem may exist. Consult
your local DIGITAL Field Service office.
Type
"DLO" and the RETURN key after the "START?" .
START?
DLO < CR >
The processor reads from the disk and, after several seconds, prints the
name of
the operating system and the system monitor.
When
the processor prints the monitor name, it indicates that the oper-
ating system is now controlling the computer and monitoring the key-
board. RSX (Real Time
Executive) uses (» as a prompt character to sig-
nal
that it is waiting for a command from the operator.
At
this time, the system is ready for the user's application . It is advisable
to copy the disk onto a spare cartridge and store the original as a backup
copy.
CHANGING A DISK CARTRIDGE
Before a disk cartridge is changed, it is very important to make certain
that the cartridge is not being accessed. On a single-user system this is
relatively easy to do . On a multiuser system, however, it is more difficult
to determine whether a cartridge is in use. Each active user must be con-
sulted before dismounting a disk cartridge . Once it is certain that there is
no risk involved in changing the
disk cartridge, use the following pro-
cedure .
1. Press the LOAD button on the RL02 drive.
a. The
disk stops rotating.
b. After several seconds, the LOAD indicator illuminates on the
RL02.
2. Remove the disk cartridge.