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EK-VTX78-UG-001

October 1977

70 pages

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Document:	DECstation Users Guide
Order Number:	EK-VTX78-UG
Revision:	001
Pages:	70
Original Filename:	http://bitsavers.org/pdf/dec/pdp8/cmos8/EK-VTX78-UG-001_DECstation_Users_Guide_Oct77.pdf

OCR Text

DECstati?"
user's gUide

OECstation
user's guide

EK-VTX78-UG-001

digital equipment corporation • maynard, massachusetts

First Edition, October 1977

Copyright © 1977 by Digital Equipment Corporation
The material in this manual is for informational
purposes and is subject to change without notice.
Digital Equipment Corporation assumes no responSibility for any errors which may appear in this
manual.
Printed in U.S.A.

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

The following are trademarks of Digital Equipment
Corporation, Maynard, Massachusetts:
DEC
DECCOMM
DECsystem-I0
DECSYSTEM-20

DECtape
DECUS
DIGITAL
MASSBUS

PDP
RSTS
TYPESET-8
TYPESET-II
UNIBUS

CONTENTS

INTRODUCTION ............................................................................................................................. 1
OPERATION ..................................................................................................................................... 3
INSTALLATION ............................................................................................................................... 7
MAINTENANCE ............................................................................................................................. 15
TROUBLESHOOTING ................................................................................................................... 17
PROGRAMMING ........................................................................................................................... 19
CENTRAL PROCESSOR UNIT (CPU) .................................................................................. 19
MEMORY ............................................................................................................................... 19
INSTRUCTIONS .................................................................................................................... 21
Memory Reference Instructions (MRls) ............................................................................ 21
Operate Microinstructions ................................................................................................ 23
Group I Microinstructions ................................................................................................. 23
Group II Microinstructions ............................................................................................... 26
Group III Microinstructions ............................................................................................. 28
I/O TRANSFERS (lOTs) ......................................................................................................... 29
Extended Memory Instruction IOTs .................................................................................. 29
Central Processor Unit lOTs ............................................................................................. 31
Real Time Clock ............................................................................................................... 33
Floppy Disk Drive System ................................................................................................. 33
Select Command (SEL) - 6750 ........................................................................................... 33
Load Command (LCD) - 6751 .......................................................................................... 33
Fill Buffer (000) ................................................................................................................. 35
Empty Buffer (OOi) ............................................................................................................ 36
Write Sector (010) ............................................................................................................. 36
Read Sector (011) .............................................................................................................. 36
Read Status (101) .............................................................................................................. 37
Write Deleted Data Sector (110) ........................................................................................ 37
Read Error Register Function (111 ) ..................................................................................... 37
Power FaiL ........................................................................................................................ 38
Transfer Data (XDR) - 6752 ............................................................................................. 38
Skip On Transfer Request (STR) - 6753 ........................................................................... )8
Skip On Error - 6754 ........................................................................................................ 38
Skip On Done - 6755 ......................................................................................................... 39
Interrupt Enable (INTR) - 6756 ........................................................................................ 39
Initialize (INIT) ~ 6757 ...................................................................................................... 39
MR 78 Interface ................................................................................................................. 40
Serial Line Unit 1 (SL U 1) ................................................................................................. 40
Serial Line Unit 2 (SLU 2) ................................................................................................. 41
Serial Line Unit 3 (SLU 3) ................................................................................................. 44
Parallel I/O ....................................................................................................................... 44

111

CONTENTS (CONT)
Page
KEYBOARD /VIDEO DISPLAY ............................................................................................ 47
Keyboard ........................ " ................................................................................................ 47
Display ............................................................................................................................. 51
Basic Cursor Movement Commands ................................................................................. 51
Line Feed (LF - 012) ................................................................................................. 51
Cursor Down (ESC B - 033 102) ................................................................................ 52
Reverse Line Feed (ESC 1 - 033 111) ......................................................................... 52
Cursor Up (ESC A - 033 101) .................................................................................... 52
Space (040) ................................................................................................................ 52
Cursor Right (ESC C - 033 103) ................................................................................. 52
Cursor Left or Backspace (BS 010) or (ESC D - 033 104) ........................................... 53
Advanced Cursor Movement Commands .......................................................................... 53
Carriage Return (CR 015) .......................................................................................... 53
Cursor Home (ESC H - 033 110) ............................................................................... 53
TAB (TAB 011) ......................................................................................................... 53
Direct Cursor Addressing (ESC Y - 033 131) ............................................................. 53
Screen Erasure Commands ................................................................................................ 53
Erase To End-Of-Line «ESC K - 033 113) ................................................................. 53
Erase To End-Of-Screen (ESC J - 033 112) ................................................................ 54
Hold-Screen Mode of Operation ................................................................................ 54
Enter Hold-Screen Mode (ESC - 033 133) .................................................................. 55
Exit Hold-Screen Mode (ESC / - 033 134) ................. ,............................................... 55
Alternate-Keypad Mode Of Operation ...................................................................... 55
Alternate-Keypad Mode (ESC = - 033 075) ............................................................... 55
Exit Alternate-Keypad Mode (ESC) - 033076) .......................................................... 55
Graphics Mode Of Operation .................................................................................... 55
Enter Graphics Mode (ESC F - 033 106) .................................................................... 55
Exit Graphics Mode (ESC G - 033 107) ..................................................................... 55
Uses of Special Symbols .................................................................................................... 56
Codes 154 - 163 ......................................................................................................... 56
Codes 142 - 154 ......................................................................................................... 56
Code 151 ................................................................................................................... 56
Codes 136 - 140 ......................................................................................................... 56
APPENDIX A

OPERATING AND ENVIRONMENTAL SPECIFICATIONS

APPENDIX B

CARE AND HANDLING OF DISKETTES

APPENDIX C

CO~TROLS AND INDICATORS

FIGURES
Figure No.
1

2
3
4
5
r

7
8
9
10
11
12
13
14
15
16
17
18
19
20
C-l
C-2
C-3

Title

Page

DECstation - Intelligent Terminal or I/O Device Configuration ................................ .1
DECstation - Typical Stand-Alone Computer Configuration ...................................... 2
DECstation - Without Floppy Disk Drive System, Operating Instructions ................. .4
DECstation - With Floppy Disk Drive System, Operating Instructions ....................... 5
MR 78 Installed ........................................................................................................... 7
Installing the Floppy Disk Diive System ...................................................................... 8
Recommended Minimum Space Requirements .......................................................... 10
DECstation with MR 78 _ Cable Connections and Switch Locations .......................... 11
DECstation with One Floppy Disk Drive System - Cable Connections and
Switch Locations ........................................................................................................ 12
DECstation with Two Floppy Disk Drive Systems - Cable Connections and
Switch Locations ....................................................................................................... 14
CPU Block Diagram ................................................................................................. 20
Main Memory ........................................................................................................... 21
Panel Memory ........................................................................................................... 21
MRI Format ............................................................................................................. 23
Group I Microinstruction Format ............................................................................. 24
Group II Microinstruction Format ............................................................................ 26
Group III Microinstruction Format .......................................................................... 28
lOT Instruction Format ............................................................................................ 30
Floppy Disk Drive System Interface I/O Format ....................................................... 34
Keyboard/Video Display Block Diagram .................................................................. 47
VT78 Terminal Keyboard .......................................................................................... 61
LA 78 Printer Operator Controls ................................................................................ 64
Q,..,.
1
L
r ...115 rrlnter vperalor Lon t··r018
.............................................................................. 6A"'t
T

,..,.

'."'"

..,......

TABLES
Table No.
1

2
3
4
5
6
7
8
9
10

Title

Page

DECstation Troubleshooting Procedures .................................................................. 17
MRI Operation Codes ............................................................................................... 22
Group I Microinstructions ......................................................................................... 24
Group II Microinstructions ....................................................................................... 26
Group III Microinstructions ...................................................................................... 29
Memory Extension Instructions ................................................................................. 30
CPU I/O Instructions ................................................................................................ 31
Panel Request lOTs ................................................................................................... 32
Real-Time Clock Instructions .................................................................................... 33
Floppy Disk Drive System Instruction Set ................................................................. 34

TABLES (CONT)
Table No.

11
12
13
14

15
1 "-

17
18
19

20
21
22
23
24
25
26

27
28
29
C-I
C-2
C-3
C-4

Title

Page

Floppy Disk Drive System Fl.!-nction Code Bit Summary ............................................ 34
Read Error Register Functions .................................................................................. 37
Error Status Register Bit Functions ........................................................................... 39
MR 78 lOTs ............................................................................................................... 40
SLU 1 lOTs ............................................................................................................... 40
Baud Rates ............................................................................................. ,""""''',,,., .. 41
SLU 2 lOTs ............................................................................................................... 42
Loading Contents of AC Into Status Enable and Interrupt Enable Flip-Flops ............ 43
Setting SL U 2 Operating Modes ............................................................................... .43
SLU 3 lOTs ............................................................................................................... 44
Parallel I/O lOTs - LA 78 Printer ............................................................................. .45
Parallel lOTs - LQP78 Printer ................................................................................... 45
Alphabetic Key Codes ............................................................................................... 48
Numeric/Symbol Key Codes ................................................................................... ,.48
Control Key Codes .................................................................................................... 49
Keypad Numeric Key Codes ..................................................................................... 50
Keypad Control Key Codes ....................................................................................... 51
Function Key Codes .................................................................................................. 52
Graphic Mode Symbols ............................................................................................. 56
VT78 Terminal Key board Controls and Indicators ................................................... 62
VT78 Terminal Auxiliary Keypad Controls and Indicators ........................................ 63
LA 78 Operator Controls and Indicators .................................................................... 63
LQP78 Printer Operator Controls and Indicators ...................................................... 64

INTRODUCTION

Your DECstation is a complete computer in a terminal. It has a processor, a 16K word memory, and a
keyboard/video display - and it does not need much more space than a conventional typewriter.
The DECstation (Figure 1) can be used as a simple I/O device, as an intelligent terminal in a distributed data processing network, or as a standalone computer. Figure 2 shows a typical standalone
computer configuration.
The system is easy to install and even simpler to operate. Just unpack the equipment, connect the
cables, and follow the simple operating steps described in this guide. Your system will be ready to run
in a matter of minutes.
Built-in diagnostics automatically check your system's performance each time you turn it on. Should a
malfunction occur, these diagnostics will also pinpoint the trouble for faster maintenance, ensuring
minimum downtime.
This guide contains information that will help you install, operate, and program your DECstation. It
also contains troubleshooting information designed to help isolate minor problems that are not equipment malfunctions. Although some RX78 floppy disk drive system information has been included in
this guide for your convenience, refer to the appropriate manuals for more detailed information.

Figure 1 DECstation - Intelligent Terminal or I/O Device Configuration

Figure 2 DECstation - Typical Stand-Alone Computer Configuration

OPERATION

If your DECstation is not equipped with a floppy disk drive system, operate the system as shown in
Figure 3. If your system has a floppy disk drive system, perform the steps shown in Figure 4.

NOTE
If your DECstation fails to operate properly or the
display does not appear as shown in Step 2 (Figures 3
and 4), refer to the troubleshooting procedures.

2. OBSERVE DISPLAY
8587-8

Figure 3

DECstation - Without Floppy Disk Drive System,
Operating Instructions

4. START PROGRAM

3. LOAD PROGRAM
(INSERT DISKETTES,
CLOSE AND LATCH
DOOR. REFER TO
APPEND!X B FOR
CARE AND HANDL.iNG
OF DISKETTES.

2. OBSERVE DISPLAY
(30 SECOND WARM

UP)

*Make sure power switch
on rear of terminal is set
to on position.
8587-9

Figure 4

DECstation With Floppy Disk Drive System,
Operating Instructions
=

INSTALLATION

All DECstation components are shipped completely assembled. To install and prepare your system for
operation, perform the foilowing step-by-step instructions.

Unpack the system components.
Be careful to avoid damaging the equipment when using sharp cutting tools to open shipping
containers.

Inspect the equipment.
Check for any physical damage that may have occurred during shipping and handling.

Install the MR 78 (if your system has one).
Insert the device into the connector at the rear of the VT78 terminal as shown in Figure 5. Tighten
the two screws on the device to secure it in place.

MR78

8587-7

Figure 5

MR 78 Installed
7

Install the RX78 floppy disk drive( s) (if your system has one).
CAUTiON
The floppy disk drive weighs approximately 29.48 kg
(65 Ib). Two people are required to lift the unit to
avoid personal injury or equipment damage.

SLIDE
11111111111
,,11111111111,,111111111

11I11I1I11::::::::lliillllllllll"

IIIIIIIIII

RX78 FLOPPY DISK
DRIVE (INSTALLED)
08-1953

Figure 6

Installing the Floppy Disk Drive System

Slide the floppy disk drive(s) into the minidesk as shown in Figure 6.
NOTE
It may be necessary to brace the table against the
wall when inserting the floppy disk drive system( s) to
prevent the table from rolling when sliding the unit
forward.

Set the VT78 terminal on the minidesk.

Arrange the DECstation in a convenient operating position.
NOTE
There are no restrictions limiting the arrangement of
the DECstation components except those imposed by
the length of the cables and the availability of adequate power outlets. All components can be table-top
mounted. Refer to Figure 7 for minimum space
requirements and Appendix A for operating and environmental specifications.

Set the terminal power switch to the OFF (down) position.
The terminal power switch is located at the rear of the VT78 terminal as shown in Figure 8.

Set the RX78 floppy disk drive system(s) ON/OFF switch(es) to OFF (if your DECstation has a
floppy disk drive system(s).
The RX78 floppy disk drive system ON jOFF switch is located at the rear of the unit as shown in
Figure 9.

Set the svstem Dower switch to 0 FF (if vour svstem has the minidesk t
..

•

- - -

-----

--- -

------------,-

The system power switch is located beneath the front of the minidesk top as shown in Figure 4.

Plug the terminal power cord into the power outlet.

If your system is comprised of a terminal and an MR 78, as shown in Figure 8, plug the terminal
line cord into a convenient power outlet. The DECstation is now ready to operate. Refer to the
preceding operation section for operating instructions. (A description of all system controls and
indicators is provided in Appendix C.)
If your system is equipped with a minidesk, as shown in Figure 9, plug the terminal into the
minidesk power strip.

/~ --X--_5~:---11
il 15"

J
I

'),i4.31cm
I~

I~
I~'
l:- --____-- -- -- ......
- - - ........ -- -- ..... "" /'
/1 I

.",---\

----

--~

--- - --- - - -:...-:.: I-1

•
I
I

I
I

27"

, 7.36cm

: I (";I

·'3

J--"}/ ---- ..... --. .....
!")
I~

I..I

______

----22"

---7 /S.13cm
/30"

=-----

6.09cm

/" '-, II
;

-'''-11

8587-10

Figure 7

Recommended Minimum Space Requirements

I W

!//;-I

[[[[[[[[[[[[(( [( [[ (0) J]] ]]]111] 11111111

-=- [[([[[[[[[[[lIII1111]]]11]]1111
[[[[[[[[l[[[[[[[[[llIJJ]]]]]]]111111111
[[[[[[[[[[[[l[[l [[flllJ I )]]1)1]]])1]]11

TERMINAL POWER
SWITCH

[[[[[[[[[[[([[[l[ [111IJJ ]J]]11]]))

[[ [[ [ [[ [[ [ [[ [ l [ l [ i [0) ] ] ] ] ] J ] ] ] ] ] 1]

-LINE

PRINTER
CONNECTOR

MR78

08-1954

Figure 8 DECstation with MR 78 - Cable Connections and Switch Locations

VT7-8
TERM!NAL'

[[[ [[ [[ [[ [[ [[ [ [ [ [ [ IoJ I ] J ] 11 ] 11111111111

/1/

-=- [[[[[[[[[[[flII1l11111111111111 ~\
[[ [[ [ [ [[ [ [ [ [ l ( [ [ [ IIII J J j I ] 1) ) 1111111111
TERMINAL
It [[[[[I ([ [[[ [[ [[ [[ II J 1111111 J 111l11if(1 POWER SWITCH
[U (l I [i i 1i j J j j ] ] 111] 11
,\1\ \
rrr rr r rf r f r f r f r I r I roll 111111 111 11 1

[[
[[
[[
[[[
[
/ II
I

LA7S/Lor
SIGNAL CABLE
PRINTER OPTION
(#BC 80H-25

t.LLLLL""Lt.LI..,-LLLL,.c"

'~~1"""'4""'~"".

MR78
(OPTIONAL)

OR #BC 80F-25)

MINIDESK
POWER
STRIP

RX78 POWER
CABLE

RX78 FLOPPY
DISK DRIVE
SYSTEM

RX780NI
OFF SWITCH

RX78 FLOPPY
DISK DRIVE
SYSTEM/TERMINAL
SIGNAL CABLE
#BC80D

SYSTEM
POWER
CORD

J~
--.-----=====-=~

08-1952

Figure 9 DECstation with One Floppy Disk Drive System - Cable Connections
and Switch Locations

Install the upper RX78 floppy disk drive system power cable (if your DECstation has a floppy disk
drive system). (Refer to Figure 9.)
If your system is not installed in the minidesk, insert one end of the cable into the floppy disk
drive system, as shown in Figure 9, and plug the other end of the cable into any convenient power
outlet.

Connect the upper RX78 floppy disk drive system/terminal signal cable. (Refer to Figure 9.)

Connect the lower RX78 floppy disk drive system power cable (if your DECstation has a second
floppy disk drive system). (Refer to Figure 10.)
If your system is not installed in the minidesk, insert one end of the cable into the floppy disk
drive system and the other into any convenient power outlet.

Connect the lower RX78 floppy disk drive system/terminal signal cable (if your DECstation has a
second floppy disk drive system). (Refer to Figure 10.)

Plug the system line cord into a convenient wall power outlet (if your DECstation has a minidesk).
(Refer to Figure 9 or 10.)

Remove the nylon tie-wrap securing the LA78 printer print head (if your DECstation has an LA78
printer).

Connect the LA 78 printer signal cable to the VT78 terminal (if your DECstation has an LA 78
printer). (Refer to Figure 10.)

Plug the LA 78 printer line cord into a convenient wall power outlet (if your D ECstation has an LA78
printer). (Refer to Figure 9 or 10.)
NOTE
If your DECstation has an LQP78 printer, contact
your nearest DIGITAL representative for assistance
in installing the printer.

Set the floppy disk drive ON/OFF switch(es) to ON.

Set the VT78 terminal power switch to the 0 N (up) position.
Your DECstation is now ready to operate. Refer to the preceding operation section for instructions. (A description of all system controls and indicators is provided in Appendix C.)

;r [ [ [[ [ [[ [

VT78

l[ [ [I! 11-]] ] )] 111111111111

TERMINAL~-=- [[ [ [ [ [ [ [ [[ [1l11l] 1] 1111 11111111

[[ [[ [[[ [ [ ( [[ [[ [ [ [ II ! I JIll] 111 1111111111
1/ [[[[[([[[UU[rlfIIIIII111l1111111111
/I [[[f[ [[[[ [[[U ( l ! [! 1111 J IJ 1] 111] 11

LIl

TERMINAL
POWER SWITCH

\ \

[[[[[[[[[[[[[[[lll[Ol]])]]J))])]1]
1

LA78/LPQ78
PRINTER OPTION
SIGNAL CABLE
(#BC 8OH-25

'J\\\

OR #BC 80F-25)

MINIDESK
POWER STRIP

SYSTEM/TERMINAL
SiGNAL CABLE
#BC80E

RX78 POWER
CABLE
RX78 FLOPPY DISK
DR IVE SYSTEM
(UPPER UNIT)

RX78 FLOPPY
DISK DRIVE
SYSTEM
(LOWER UNIT)

SWITCH

RX18 POWER
CABLE
08-1951

Figure 10

DECstation with Two Floppy Disk Drive Systems - Cable Connections
and Switch Locations

MAINTENANCE

The keyboard and auxiliary keypad keys are the only moving parts of the DECstation and require no
preventive maintenance. The terminal and floppy disk drive (if applicable) can be cleaned with soap or
any mild detergent and water. Cleaners with solvents should not be used.
There are several openings in the case through which liquids, coins, paper clips, or other objects could
fall, thereby disrupting circuit operation. For this reason, avoid setting drinks and metal objects on top
of the terminal or using excessive water to clean the termina1.
The electronics in the keyboard and keypad area are close to the exterior. Rubbing the keys with a dry
or barely moist cloth should suffice to clean them. Do not remove the key caps to clean the keys more
thoroughly; damage may result to the switch contacts if caps are replaced incorrectly.

TROUBLESHOOTING

Even the most sophisticated and reliable system can malfunction. However, many malfunctions are
not equipment malfunctions at all, but are simple problems such as accidently turning down the terminal intensity control or unplugging the line cord.

If your system fails to operate or operates improperly, check the symptoms and possible causes listed
in Table 1 before calling your DIGITAL service representative.
NOTE
If problems cannot be corrected using these quick
checks, contact your nearest DIGITAL service representative.

Table 1 DECstation Troubleshooting Procedures
Symptom

Possible Cause

Corrective Action

Plug in the line cord.
System completely inoperative Line cord unplugged.
(no response or sound when
Check appropriate building
power ONJOFF switch is set Power receptacle dead.
I fuse or circuit breaker.
I
to ON.
Terminal power switch in the
Set the terminal power switch
off position.
(rear of terminal) to the on
(up) position.
Blown fuse.
Replace with same type fuse.
System powered up but display does not appear.

Intensity control on rear of
terminal turned down.

Adjust intensity control for
desired display brightness.

ABCDEF display absent or
letter missing.

Circuit malfunction.

Turn the system off, then on
again. Check to see if DC OK
and CP OK indicators at the
rear of the terminal are on. If
problem persists call your
DIGITAL service representative.

Table 1 DECstation Troubleshooting Procedures (Cont)
Symptom

I rOSSI
~ "b Ie \....ause

Display correct but program
cannot be loaded.

Loose MR 78 program loading
device (if DECstation is equipped with MR78 device).

......

Tighten the two screws securing the MR 78 to the rear of
the terminal.

If DECstation is equipped
with floppy disk drive system(s):
a.

Floppy disk drive
s y s tern power
ON /OFF switch set
to OFF.

Set the floppy disk drive systern power ON/OFF switch
(rear of unit) to ON.

Diskette inserted
improperly into
floppy disk drive
system.

Reinsert diskette properly.

Defective diskette

Substitute diskette with one
known to be good. Try to load
program again.

Floppy disk system
line cord unplugged.

Plug line cord in power terminal strip at rear of stand (Figure 9 or 10).

Floppy disk drive II Check cable connections (Figsystem/terminal in- ure 9 or 10).
terface cable loose
or unplugged.

PROGRAMMING

CENTRAL PROCESSOR UNIT (CPU)
The processor, shown in Figure 11, is comprised of six 12-bit data registers, control logic, timing logic,
and an arithmetic logical unit (ALU).
The ALU performs both arithmetic and logical operations such as AND, TAD, and logical OR. ALU
operations involve two operands, one held in the accumulator (AC) and the other in a memory location.
The AC is a 12=bit data register used in ALU operations. Data is fetched from memory to the AC or
transferred from the AC to memory. The AC can be cleared, complemented, incremented, tested, and
rotated under program control.
Link (L) is a I-bit flip-flop that serves as a high-order extension to the AC (a carry bit).
The program counter (PC) contains the address, in memory, from which the next instruction is
fetched. During an instruction fetch, the PC determines the instruction address and is incremented by
one. If a branch to another address in memory' is requested (Le., a JMP or JMS instruction), a new
address is loaded into the PC. Several operate and lOT instructions will produce a program skip.
These instructions cause the PC to be incremented by one a second time, thus skipping the next
sequential instruction.
The muitipiier quotient (MQ) register is a temporary register used to exchange data, OR data; or store
data received from the AC.
A more detailed description of the functional operation of the CPU is provided in the DECstation
Technical Manual.
MEMORY
There are two types of memory in the VT78 terminal - main memory and panel memory. Main
memory (Figure 12) consists of a volatile 16K random access memory (RAM) divided into 4K blocks
(fields) of memory. Each field (0-3) contains a 4K 12-bit RAM memory that is used to store a user's
main program and data.
Panel memory (Figure 13) uses both read-only memory (ROM) and RAM memories. Panel memory
contains 4K of memory -addresses. Each address contains 12 bits of data or an instruction. The internal
diagnostics, MR 78 bootstrap, and disk bootstrap programs are stored in panel memory at addresses
6000 through 7777 (octal). Because these programs need several addresses in which to store register
information, two pages of RAM have been provided at location 0000 to 3778 of this field of memory.
Locations 4008 through 5777 contain no memory.

RESET, RUN/HL T
DMAREO,CPREQ
INTREQ

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

MTA
E Ji:}SGTEAN _
-

{J- =SUTP~T
PL_A
.

====:==~-. . . CONTROL
DEVICE

LXMAR, DEVSEL.
SWSEL. MEMSEL
CPSEl.

[~
LINK - -...- - - - ~-------

LATCH

SKP, CO, C1, C2
MEMORY &

ALJ~
__jJ
--...--------------~

I:::

STATE
CONTROL

CRYSTAL
XTA. X'TB. XTC. DMAGNT.
INTGNT.IFETCI-I. D/\TAF. RUI'II

08·18f;9

Figure 11

CPU Block Diagram

7777a

PAGE 37s
PAGE 36s

FIELD 3

FIELD 2
FIELD 1
FIELD 0

1"\

[16K(MAX))

LOC 177a
LOC 1769

PAGE7

LOC 7

PAGE6

lOC 6

PAGE S

LOCS

PAGE4

LOC4

PAGE3

LOC3

177a = 128,0

,.,;

LOC2

PAGE2

PAGt;1

LOC 1

017781
OOOOa ; - - -......

PAGE 0

lOCO
j200a LOCATIONS)
1 MEMORY PAGE

i40s PAGES)
1 MEMORY FIELD

08-1932

Figure 12

7777a

PAGE 37a [ROM)
PAGE 36a jROMj

--------PAGE 31. [ROM)

12. PAGES

LOC 1778
LOC 1768

60008

PAGE 3D. [ROM]
NO MEMORY

NO MEMORY
PAGE 1 [RAM)
PAGE 0 [RAM]

Main Memory

LOCS
LOC4
LOC3
LOC2
LOC 1
LOCO

0377a
0177a
OOOOa

200alOCATIONS
1 MEMORY PAGE

10sROM PAGES
2 RAM PAGES

1 FIELD FOR CONTROL
PANEL MEMORY
08-1933

Figure 13

Panel Memory

INSTRUCTIONS
~1emory Reference Instructions (~lRIs)
The MRls cause the computer to operate on the contents of a memory location or to use the contents
of a memory location to operate on the AC.

Figure 14 shows the MRI format. Bits 0 through 2 specify the function (op code) to be executed while
the lower order bits, 3 through 11, give the operand address. Table 2 lists the mnemonics for the five
MRls, their octal codes, and the operations performed.

Table 2
OP Code

Mnemonic

AND

MRI Operation Codes

Time (J.Ls)

Operation*

Description

5.92

D
I
A

The content of the effective location is ANDed
with the contents of the
AC. The result is deposited into the AC (link and
MQ register are unt
cnanged).

8.8
9.4

TAD

5.92

8.8
9.47

ISZ

D
I
A

The contents ofihe effective location are added to
the contents of the AC
using 2's complement
arithmetic. The result is
deposited into the AC.
The link bit is set (1); otherwise, link and ~1Q reg~
ister are unchanged.

The content of the effective location is incremented, then tested
for a zero. If the result is
zero, the next sequential
instruction is skipped;
otherwise, the next
sequential instruction is
fetched. The AC, link,
and MQ register are unchanged.

9.47
12.4
13.0

I
A

DCA

6.5
9.47
10.0

D
I
A

The contents of the AC
are deposited into the effective location. The AC
is then cleared. Link and
MQ register are unchanged.

JMS

6.5
9.47
10.0

D
I
A

The contents of the PC
are stored at the effective
location and the effective
location, + 1, is loaded
into the PC. This is a
jump to subroutine instruction (link, AC, and
MQ are unchanged).

JMP

5.92

D
I
A

The effective address is
loaded into the PC (link,
AC, and MQ are unchanged).

8.8
9.47
Note:

*D =
I =
A =

Direct
Indirect
A utoindexing

-------------~--------------

----~----'
OP CODE 0-5

PAGE ADDRESS

MEMORY PAGE

~INOIRECT

ADDRESSING

O=PAGEO
1 =CURRENT PAGE
O=DIRECT
1 =INDIRECT
08-1926

Figure 14

MRI Format

Bits 3 through 11 specify an address on one of two pages of memory. The page of memory is determined by bit 4. If bit 4 is a 0, the address specified will be in location 0000 to 0177 of page O. If bit 4 is a
1, the location will be in the current page (the page on which the instruction is located). Bits 5 through
11 determine the absolute address on the page. For example, if an instruction is located at address 503
and bits 3 through 11 equal 364, the operand address will be in location 164 of the current page or at
address 564.

After an address has been determined, the processor examines bit 3 to determine if this address is the
operand address (direct addressing) or a pointer to the operand address (indirect or deferred addressing). If bit 3 equals 0, the processor operates on the address specified. If bit 3 equals 1, the processor
uses the data from this page address as the 12-bit address of the operand. Notice that although the
page addressing method restricts direct addressing to a maximum of 256 locations, indirect addressing
allows access to all 4096 locations in the current memory field. For example, if the instruction is
located at address 503 and instruction bits 3 through 11 equal 764, and if the contents of location 564
were 3015, the effective address would be 3015.
Autoindexing locations 10-17 are treated in a special manner. If an indirect reference is made through
one of these addresses, the address is incremented before being used. No facility for skipping is provided when a location has been incremented to zero. To use autoindexing locations, the memory page
(MP) bit must be cleared, even if the instructions are on page zero.
Operate Microinstructions
The operate microinstructions are identified by an op code of 7 (bits 0-2 = Ill). Operate instructions
do not specify a memory address; instead, the remaining nine bits specify the operation to be performed.
The operate instructions are subdivided into three major classes - Group I, Group II~ and Group III as described in the following paragraphs. Group I microinstructions provide manipUlation of the AC
and the link. Group II provides testing of the AC and link. Group III allows manipulation of the MQ.
Group I l\1icroinstructions
Figure 15 shows the format of a Group I microinstruction.

00
1

II II II II II II
1

CLA

Cll

l_ _ _ _
___

CMAI CMl I : : :

•••

II ..:~Il"- II +;

lAC

1
I

I"-y-J

78 FOR ALL

MICRO INSTRUCTIONS

GROUP 1
08-1927

Figure 15

Group I Microinstruction Format

The Group I microinstructions allow the programmer to manipulate the AC and the link bit. The
functions cause the AC to be cleared, complemented, incremented, rotated to the left or right one bit,
rotated to the left or right two bits, or byte swapped. The link can be cleared, complemented, or shifted
right or left with the AC. Any combination of iogically nonconflicting bits can be used unless bits 8
and 9 are both set.
Table 3 lists the Group I microinstructions, their assigned mnemonics, and their operations.

Table 3

Group I Microinstructions

Octal

Mnemonic

Sequence*

Times (JLs)

Description

7000

NOP

5.92

No operation.

7001

lAC

5.92

Increment AC by 1.
Carry out of ACO com1.
plemenus 1:Un1\..
_1

7002

BSW

8.84

Byte swap. Right six bits
are exchanged with ieft
six bits (ACO exchanged
with AC6; ACI with
AC7; etc). Link is not
changed.

7004

RAL

8.88

Rotate AC left one bit.
ACO rotated into link.
Link rotated to AC bit
II.

7006

RTL

8.88

Rotate AC left two bits.
ACI rotated into link.
Link rotated to AC bit

10.
7010

RAR

8.88

Rotate AC right one bit.
ACll rotated into link.
Link rotated to AC bit O.

Table 3
l\lnemonic

Group I Microinstructions (Cont)

Sequence*

Time (j.Ls)

Description

7012

RTR

8.88

Rotate AC right two bits
ACI0 rotated into link.
Link rotated to AC bit 1.

7020

CML

5.92

Complement link.

7040

CMA

5.92

Complement AC.

7041

CIA

2,3

5.92

Complement AC and increment AC. (Forms the
2's complement.)

7100

CLL

5.92

Clear link (L=O).

7104

CLLRAL

1,4

8.88

Clear link then rotate AC
and link left.

7106

CLLRTL

1,4

8.88

Clear link then rotate AC
and link twice left.

7110

CLLRAR

1,4

8.88

Clear link then rotate AC
and link right.

7112

CLLRTR

1,4

8.88

Clear link then rotate AC
and link twice right.

7120

STL

1,2

5.92

Set the link (clear, then
complement link).

7200

CLA

5.92

Clear the AC
(AC=OOOO).

7201

CLAIAC

1,3

5.92

Clear the AC then increment the AC
(AC=OOOI).

7204

GLK

1,4

8.88

Get the link (AC is
cleared; the A C and link
are rotated left).

7240

STA

5,92

Set the AC (Ae=7777).

7300

CLACLL

5.92

Clear the AC and link.

*Logical Sequence
I = CLA, CLL
2 = CMA, CML
3 = lAC
4 = RAR, RAL, RTR, RTL, BSW

Group II Microinstructions
Group II microinstructions allow the programmer to test the data in the AC and! or the link using the
skip instructions. For Group II microinstructions, bit 3 must be a 1 and bit i i must be a O. Figure 16
shows the format of a Group II microinstruction.
A skip microinstruction requiring bit 8 to equal zero cannot be programmed with instructions requiring that bit 8 equals a 1.
Table 4 lists the Group II microinstructions, their assigned mnemonics, and their operations.

CLA

SMA
SPA

SZA
SNA

...Q...

OSR

HLT

7, F;;; ALL

SZL

JyI

GROUP II

MiCROINSTRUCTIONS

GROUP !!
08-1928

Figure 16

Group n Microinstruction Format

Table 4

Group II Microinstructions

Octal

Mnemonic

Sequence·

Time (J,Ls)

Description

7400

NOP

5.92

No operation (See Group
I microinstruction).

7402

HLT

5.92

HALT - Stops main
memory processing. The
VT78 displays a series of
status words defining the
state of the program and
waits for the operator to
press the START button.

7404

OSR

8.88

Clear AC. Load AC with
preselect and MR 78 status.
Bits 8-11 = Preselect
Bits 3- 5 = Number of
binary program
Bit 0 = MR 78 is present.

7410

SKP

5.92

SKIP (PC is incremented
by one, next instruction
is skipped).

7420

SNL

5.92

Skip on nonzero link.

7430

SZL

5.92

Skip on zero link.

Table 4
Octai

fi.lnemonic

7440

Group II Microinstructions (Cont)

I Sequence*

Time (J.Ls)

Description

SZA

5.92

Skip on zero AC.

7450

SNA

5.92

Skip on nonzero AC.

7460

'SZA SNL

5.92

Skip on zero A C, or skip
on nonzero link or both,

1J.

5.92

Skip if AC is nonzero
and link is zero.

"7"'''70
/"'t/V

7500

SMA

5.92

Skip on minus AC. [If
AC(O) = 1, skip.]

7510

SPA

5.92

Skip on positive AC. [If
AC(O) = 0, skip.]

7520

SMASNL

5.92

Skip on minus AC or
skip nonzero link or
both.

7530

SPA SZL

5.92

Skip if AC is positive and
link is zero.

7540

SMASZA

5.92

Skip on minus AC or
skip on zero AC or both.

7550

SPASNA

5.92

Skip if AC is positive and
nonzero.

7560

SMASZASNL

5.92

Skip on minus AC or
skip on zero AC or skip
on nonzero link or all.

7570

SPASNASZL

5.92

Skip if link is zero and
AC is positive and nonzero.

7600

CLA

5.92

Clear AC.

7604

LAS

1,3

8.88

OR with preselect and
MR 78 status.
Bits 8-11 = Preselect
Bits 3- 5 = Number of
binary program
Bit 0 = MR78 is present

7640

SZACLA

1,2

5.92

Skip on zero AC then
clear AC.

Table 4

Group II Microinstructions (Cont)

Octal

Mnemonic

Sequence·

Time (fJ,s)

7650

SNACLA

1,2

5.92

Skip on nonzero AC then
clear AC.

7700

SMACLA

1,2

5.92

Skip on minus AC then
clear AC.

7710

SPA CLA

1,2

5.92

Skip on positive AC then
clear AC.

Description

*Logical Sequence
1=
2=
3=
4=

When bit 8 is 0 - either SMA, SZA or SNL
When bit 8 is 1 - Both SPA, SNA and SZL
CLA
OSR
HLT

Group III Microinstructions
Figure 17 shows the format of a Group III microinstruction.
These microinstructions allow the programmer to manipulate the MQ register. Bits 3 and 11 must be
set (1) for Group III microinstructions. Although bits 6, 8, 9, and 10 are not used, it is recommended
that they always remain 0 so that code generated on this system will be compatible to computers that
are equipped with extended arithmetic elements.
Table 5 iist the Group Hi microinsiructions, their assigned octal numbers, and their operations.

\.'---7-8

-F~

ALL

'---'

GROUP III

MICROINSTRUCTIONS

~ DON'T CARE

GROUP III

08-1929

Figure 17

Group III Microinstruction Format

Table 5
Octal

Mnemonic

7401

NOP

7421

Group III Microinstructions

Sequence*

Time (J.Ls)

Description

5.92

No operation.

MQL

5.92

MQ register load. AC is
loaded into MQ, AC is
then cleared.

7501

MQA

5.92

MQ register is loaded
into AC. MQ is ORed
with AC; results loaded
in AC.

7521

SWP

5.92

Swap MQ and AC.

7601

CLA

5.92

Clear AC.

7621

CAM

5.92

Clear AC and clear MQ.

7701

ACL

5.92

Clear AC, then load MQ
into AC.

7721

CLASWP

5.92

Load MQ into AC, clear
MQ.

* Logical Sequence
1 = CLA
2 = MQA, MQL
3 = SWP

I/O TRANSFERS (lOTs)
The I/O instructions (0-2) are identified by op code 6. The control bits (9-11) define the function to be
performed. Bits 3-8 represent the device selection code that specifies which device is intended. These
six bits will accommodate a maximum of 64 I/O devices. Some of these device codes are used for CPU
I/O and memory extensions. All instruction times are 10 J.Ls. Figure 18 shows the complete lOT
instruction format.
Extended Memory Instruction lOTs
Memory extension is necessary because the maximum number of memory locations that can be
defined by 12 bits is 4096 addresses. The DEC station system uses 16K memory; therefore, an additional two bits are needed to define any addresses above 4K. Memory extension instructions use
registers to define the bits of addressing. These registers are the instruction field (IF), data field (DF),
instruction buffer (IB), and the save field (SF) registers.
A list of the memory instructions and a brief description of each is provided in Table 6.
The IF is a 2-bit register that serves as an extension to the PC. Instructions and directly addressed
operands are obtained from the IF.

I
l

______ __- __
~

---

I
I

--~'"---"""---I

DEVICE CODE SELECTION

68 FOR ALL
lOT INSTRUCTIONS

0
;t"

CONTROL BITS

08-1930

Figure 18

Table 6

lOT Instruction Format

Memory Extension Instructions

Octal

Mnemonic

Time (J.Ls)

Description

62Nl

CDF

Change the data field to N (N may be 0-7).

62N2

CIF

At the next JMP or JMS, change instruction
field to N. Inhibit interrupts until change occurs (N may be 0-3).

62N3

CDFCIF

Combined CDF and CIF.

6214

RDF

Read the data field (inclusive OR) into bits 7
and 8 of AC. Note: Bit 6 will always be zero.

6224

RIF

Read the instruction field (inclusive OR) into
bits 7 and 8 of AC. Bit 6 will always be zero.

RSB

Read (inclusive OR) the ISF and DSF into
bits 7 and 8 and bits 10-11 of the AC, respectively.

RMF

Restore memory fields to their state prior to
last interrupt by loading DSF into DF and
ISF into IB and inhibiting interrupts. At the
time of next JMP or JMS, IB is loaded into IF
and the interrupt inhibit is removed.

6244

The IB is a 2-bit register that serves as a holding register whenever a change instruction field (CIF) or
equivalent instruction is given. When a CIF instruction is requested, the new field is loaded into the IB
and interrupts are inhibited. At the next JMP or JMS, the IB is loaded into the IF and interrupts are
allowed. For JMP instructions, the entire instruction cycle takes place in the old field; the new field is
not selected until the next instruction fetch. In the case of JMS instructions, the execute phase (depositing the old PC) takes place in the new field. The double buffedng of the IF allows the programs to
JMS or JMP to any address in the new memory field.
The DF is a 3-bit register that serves as an extension to the memory address register. Indirect AND,
TAD, ISZ, and DCA instructions access the current data field.

The save field register is a 4-bit register consisting of two halves - the instruction save field (ISF) and
the data save field (DSF). Upon recognition of an interrupt, the contents of the IF and DF are loaded
into the ISF and nSF, respectively. The IB, IF, and DF are cleared, allowing field 0 to be entered for
interrupt handling. The save field is the field in which to return after the interrupt has been processed
and the restore memory field (RMF) instruction has been given.
Central Processor Unit lOTs
The central processor lOTs (Table 7) control the interrupt system and panel memory.

If the interrupt system is enabled, the CPU will respond to an interrupt request by storing its PC in
location 0, field 0, disabling the interrupt system. The interrupt request line being driven low by any
interface will cause an interrupt. The program must then enter a skip chain to determine what I/O
device caused the interrupt and proceed to service that device. After servicing, the interrupts can be
turned on again.

Table 7

CPU I/O Instructions

Octal

Mnemonic

Time (~s)

Function

6000

SKON

Skip if interrupt system is enabled. Turn the
interrupt of[

6001

ION

If the CPU is in panel mode, exit panel mode
after fetching next instruction. If the CPU is
fetching from main memory, turn interrupt
system on after next instruction fetch.

6002

10F

Turn the interrupt off.

6003

SRQ

Skip if interrupt bus is low.
NOTE
Due to the manner that the memory
extension control inhibits interrupts,
this lOT will not skip if a CIF has
been issued and a JMP or JMS has
not been encountered.

6004

GTF

Get Flags
Bit 0 = Link Bit
Bit 1 = 0
Bit 2 = 1 if interrupt bus (low)
Bit 3 = 0
Bit 4 == interrupt enable flip-flop
Bit 5 = 0
Bit 6 = 0
Bit 7 = ISFI
Bit 8 = ISF2
Bit 9 = 0
Bit 10 = DSFI
Bit 11 = DSF2

Tabie 7

CPU iiO instructions (Cont)

Octal

Mnemonic

Time (/-Ls)

Function

6005

RTF

Restore flags. Bit 0 is shifted left into the link,
bits 7 and 8 are loaded into IB, bits 10 and 11
are loaded into DF, and interrupts are
enabled.

6007

CAF

Clear the AC, link, and interrupt. Clear all
peripheral flags, and set all interrupt enable
flip-flops (except LQP78 if used).

6071

PRS

Read panel status into the AC. Then clear
panel status.
Bit 0 = Power turn on.
Bit 1 = START switch.
Bit 2 = CPU halted.
Bit 3 = lOT 6073 (PRQ) was fetched in main
memory.

6072

PST

Complement the CPU's run flip-flop.

6073

PRQ

Panel request - enter panel mode, set bit 3 of
the panel status word. The PRQ processor in
panel memory retrieves the word following
the PRQ instruction as an address in panel
memory and jumps to that address. (Refer to
Table 8.)

6074

PER

Turn OFF the CPU OK light (used in conjunction with internal diagnostics to indicate
condition of CPU - normally on).

Table 8

Panel Request lOTs

Address

Function

6002

Initiates dumb terminal mode (VT78 terminal functions as a
conventional terminal,
via SL U 2, with a host
computer).

6003

Initiates start routine.
Produces same results
as pressing terminal
START switch.

6200

Run floppy disk drive
bootstrap.

Interrupt must be off.

6201

Run MR78 loader.

Interrupt must be off.

Restrictions

Real Time Clock
The real time clock interrupts the processor every 100 Hz if the interrupt enable is set. A skip instruction causes the program to skip an instruction if the clock flag is set. After testing and skipping on the
flag, the programmer must clear the flag.

Table 9

Real-Time Clock Instructions

Mnemonic

Octal Code

Function

CLLE

6135

In!Hi thp
lntprrllnt
pn!:lhlp frnM"1 thp A r
..
.a..a. ... ,.,...., .......... .t' ..

.A.J"'_~

.LA..,

.-.".&.&. .... IL,.I' ... """

......

.....,.&..1..1.

......... " " , 1 . 1 ' - "

.I. ....

If AC 11 = 1, set interrupt enable.
If A C 11 = 0, clear interrupt enable.
CLCL

6136

Clear clock flag.

CLSK

6i3i

Skip on clock flag.

Floppy Disk Drive System
The floppy disk drive system interface allows two modes of data transfer between the VT78 and the
floppy disk drive system: 8-bit and 12-bit word lengths. In the 12-bit mode, 64 words are written in a
diskette sector, requiring two sectors to store one page of information. The diskette capacity in this
mode is 128,128 12-bit words (1,001 pages). In the 8-bit transfer mode, 128 8-bit words are written in
each sector. Diskette capacity is 256,256 8-bit words, which is a 33 percent increase in diskette capacity
over the 12-bit mode. The 8-bit mode must be used for generating IBM compatible diskettes. Since the
12-bit mode does not fully pack the sectors with data, the hardware puts in extra Os. Data transfer
requests occur 23 j,LS after the previous request was serviced for 12~bit mode (18 j,LS for the 8-bit mode).
There is no maximum time between the transfer request from the floppy disk drive system and servicing that request by the processor. This allows the data transfer to and from the floppy disk drive
system to be interrupted without loss of data.
The floppy disk drive system instruction set is listed in Table 10 and described in the following paragraphs.
Select Command (SEL) - 6750 - This command determines which dual floppy drive will be selected.
Load Command (LCD) - 6751- This command transfers the contents of the AC to the interface register
and clears the AC. If AC bit 4 is zero, the floppy disk drive system begins to execute the function
specified in AC 8, 9, and 10 (Figure 19) on the drive specified by AC 7. A new function cannot be
initiated unless the floppy disk drive system has completed the previous function.
The function codes (bits 8, 9, and 10) are summarized in Table 11.
The DRV SEL bit (bit 7) selects one of the two floppy disk drive systems to perform the I/0 function.
When AC 7 = 0, drive 0 is selected. When AC 7 = 1, drive 1 is selected.
The 8- or 12-bit (bit 5) selects the length of the data word. When AC 5 = 0, the 12-bit mode is selected.
When AC 5 = 1, the 8-bit mode is selected.

Table 10

Floppy Disk Drive System Instruction Set

Octai

~lnemonic

Time (jis)

Function

6750

SEL

10.2

Select RX78 drive pair A if AC 11 = o or
drive pair B if AC 11 = 1.

6751

LCD

10.2

Load command, clear AC.

6752

XDR

10.2

Transfer DATA register.

6753

STR

10.2

Skip on transfer request.

6754

SER

10.2

Skip on errors.

6755

SDN

10.2

Skip on done.

6756

INTR

10.2

SET /CLEAR interrupt enable with AC 11.

6757

INIT

10.2

Initialize.

FU NCTION

NOT

USED
8/12

DRV

SEL

CP -1~14

Figure i 9

Floppy Disk Drive System Interface I/O Format

Table 11

Floppy Disk Drive System Function Code Bit Summary
Code

Function

000

Fill buffer
Empty buffer
Write sector
Read sector
Not used
Read status
Write deleted data sector
Read error register

001
010
011
100

101
110
III

The maintenance bit (bit 4) can be used to diagnose the interface under off-line and on-line conditions.
The off-line condition exists when the cable is disconnected from the floppy disk drive system. The online condition exists when the cable is connected.
In the on-line mode, if an LCD lOT is issued when AC 4 = 1, the maintenance flip-flop will be set
causing assertion of RUN on the following XDR to be inhibited. All data register transfers are then
forced into the AC. The maintenance bit allows the interface register to be written and read for maintenance checks. The nlaintenance flip-flop is cleared by initialize or by an LCD lOT when AC 4 = o.
I n the off-line mode, the contents of the interface buffer cannot be guaranteed immediately following
the first LCD lOT, which sets the maintenance flip-flop. However, successive LCD lOTs will guarantee the content of the interface register. The content of the interface register can then be verified by
using the XDR lOT to transfer the content into the AC.
The maintenance flip-flop also sets the skip flags, which will remain set as long as the maintenance flipflop is set. Skipping will not clear the flags as long as the maintenance flip-flop is set. Setting and then
clearing the maintenance flip-flop will leave the skip flags in a set condition. The skip lOTs can then be
issued to determine whether or not a large portion of the interface skip logic is working correctly.
The maintenance flip-flop can also be used to determine if the interface is capable of generating an
interrupt. The maintenance flip-flop is set, thus causing the done flag to set. The interrupt enable flipflop can be set by issuing an INTR lOT when AC bit i 1 = i. The combination of DONE and interrupt
enable should generate an interrupt.
The maintenance flip-flop can be used to test the INIT lOT. This is accomplished by setting the
maintenance flip-flop and then clearing it to generate the flags. IN IT lOT is then executed. If execution
of INIT lOT is successful, all of the flags and the interrupt enable flip-flop should be cleared if previously set.
fn the on-line mode, use of the maintenance bit should be restricted to writing and reading the interface register. The same procedure described to write and read the interface register in the off-line mode
should be implemented in the on=line mode. Exiting frem the en-line maintenance bit mode should be
finalized by an initialize to the floppy disk drive system.
Fin Buffer (000) - The fill buffer function is used to load the floppy disk drive system sector buffer
from the processor with 64 words in the 12-bit mode or 128 words in the 8-bit mode. This instruction
only loads the sector buffer. To complete the transfer to the diskette, the write sector function must be
performed. The buffer may also be read back by means of the empty buffer function to verify the data.
Upon decoding the fill buffer function, the floppy disk drive system will set the transfer request (TR)
flag signaling a request for the first data word. The TR flag must be tested and cleared by the processor
with the skip on transfer request (STR) instruction prior to each successive XDR lOT. The data word
can then be transferred to the interface register by means of the XDR lOT. The floppy disk drive
system then moves the data word from the interface register to the sector buffer and sets the TR flag as
a request for the next data word. This sequence is repeated until the sector buffer has been loaded.
After the last word has been loaded into the sector buffer, RXES (parity error and eRe error) is
moved to the interface register and the floppy disk drive system sets the done flag to indicate the
completion of the function. The processor does not have to count the data transfers. Any XDR command, after done is set, will load the RXES status word into the AC. The sector buffer must be
completely loaded before the interface will set the done flip-flop and recognize a new command. An
interrupt would now occur if the interrupt enable flip-flop were set.

Empty Buffer (001) - This function moves the contents of the sector buffer to the processor. When the
empty buffer function is decoded, RXES bits 10 and 11 are cleared, and the TR flag is set with the first
data word in the interface register. This TR flag acknowledges the request for a data transfer from the
buffer to the processor. The flag must be tested and cleared, then the word can be moved to the AC by
an XDR command. The direction of the transfer for an XDR command is controlled by the floppy
disk drive system. The TR flag is set again with the next word in the interface register. This sequence is
repeated until all of the words have been transferred, thus emptying the sector buffer. The done flag is
set after the RXES is moved in the interface register to indicate the end of the function. An interrupt
would now occur if the interrupt enable flip-flop were set.

NOTE
The empty buffer function does not destroy the content of the sector buffer.
Write Sector (010) - This function transfers the content of the sector buffer track and sector on the
diskette into the interface register. Upon decoding this function, the interface clears bits 10 and 11
(parity error and eRe error) of the RXES and sets the TR flag, signifying a request for the sector
address. The TR flag must be tested and cleared before the sector address can be loaded into the
interface register by means of the XD R command.
The TR flag is set again, signifying a request for the track address. The TR flag must be tested and
cleared, then the binary track address may be loaded into the interface register by means of the XDR
command.
The floppy disk drive system tests the supplied track address to determine if it is within the allowable
limits. If it is not, the RXES is moved to the interface register, the error and done flags are set, and the
function is terminated.
If the track address is legal, the floppy disk drive moves the head of the selected drive to the selected
track, locates the requested sector, transfers the contents of the sector buffer and a CRC character to
that sector, and sets the done flip-flop. Any errors encountered in the seek operation will cause the
function to cease, the RXES to be loaded into the interface register, and the error and done flags to be
set. If no errors are encountered, the RXES is loaded into the interface register and only the done flag
is set.

NOTE
The write sector function does not destroy the content of the sector buffer.
Read Sector (011) - This function moves a sector of data from a specified track and sector on the
floppy disk to the sector buffer. Upon decoding this function, the RX8E clears RXES bits 5, 10, and 11
(deleted data, parity error, and CRC error, respectively) and sets the TR flag signifying the request for
the sector address. The flag must be tested and cleared. The sector address is then loaded into the
interface register by means of the XDR command. The TR flag is set again signifying a request for the
track address. The flag is tested and cleared by the processor, and the track address is then loaded into
the interface register by an XDR command. The legality of the track address is checked by the floppy
disk drive system. If illegal, the error and done flags are set when RXES moves to the interface register,
and the function is terminated. Otherwise, the floppy disk drive system moves the head to the specified
track, locates the. specified sector, transfers the data to the sector buffer, and computes and checks
CRe for data. Ifno errors occur, the done flag is set with the RXES in the interface register. If an error
occurs anytime during the execution of the function, the function is terminated by setting the error and
done flags with RXES in the interface register. A detection of CRC error results in RXES bit 11 being
set. If a deleted data mark was encountered at the beginning of the desired data field, RXES bit 5 is set.

Read Status (101) - Upon decoding this function, the floppy disk drive system moves the RXES to the
interface register and sets the done flag. The RXES can then be read by the XDR.
NOTE
The average time for this function is 250 ms. Excessive use of this function will result in substantially
reduced throughput.
Write Deleted Data Sector (110) - This function is identical to the write data function except that a
deleted data mark is written prior to the data field rather than the normal data mark. RXES bit 5
(deleted data) will be set in the interface register upon completion of the function.
Read Error Register Function (111) - The read error register function can be used to retrieve explicit
error information upon detection of the error flag. Upon receiving this function, the floppy disk drive
system moves an error code to the interface register and sets the done flip-flop. The interface register
can then be read via an XDR command and the code interrogated to determine which type of failure
occurred.
Refer to Table 12 for a list of the read error register functions.

Table 12

Read Error Register Functions

Octal
Code

Error Code Meaning

0010

Drive 0 failed to see home on initialize.

0020

Drive 1 failed to see home on initialize.

0030

Found home when stepping out 10 tracks for INIT.

0040

Tried to access a track greater than 77.

0050

Home was found before desired track was reached.

0060

Self-diagn ostie error.

0070

Desired sector could not be found after looking at 52 headers (2 revolutions).

0110

More than 40 J,tS and no SEP clock seen.

0120

A preamble could not be found.

0130

Preamble found but no I/0 mark found within allo\vable time span.

0140

CRC error on what was thought to be a header.

0150

The header track address of a good header does not compare with the desired
track.

0160

Too many tries for an IDAM (identifies header).

Table 12

Read Error Register Functions (Cont)

Octai
Code

Error Code Meaning

0170

Data AM not found in allotted time.

0200

CRC error on reading the sector from the disk. No code appears in the ERREG.

0210

All parity errors.

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

Move the drive 1 head position mechanism to track O.
Clear any active bits.
Read sector 1 of track 1 of drive O.
Set the RXES initialize done bit, after which done is again asserted.

Transfer Data (XDR) - 6752 - With the maintenance flip-flop cleared, this instruction operates as
follows. A word is transferred between the AC and the interface register. The direction of the transfer
is governed by the floppy disk drive system OUT L line. The length of the word transferred is determined by the mode selected (8- or 12 bit). When done is negated, executing this instruction indicates to
the floppy disk drive system that the last data word supplied by the floppy disk drive system has been
accepted by the processor, and the floppy disk drive can proceed; or that the data or address word
requested by the floppy disk drive system has been provided by the processor and the floppy disk drive
system can proceed.
A data transfer (XDR) from the AC always leaves the AC unchanged. If operation is in the 8-bit mode,
AC bits 0-3 are transferred to the interface register but are ignored by the floppy disk drive system.
Transfers into the AC are 12-bit jam transfers when in the 12-bit mode. When in the 8-bit mode, the 8bit word is ORed into AC 4-11, and AC 0-3 remain unchanged. When the floppy disk drive system is
done, this instruction can be used to transfer the status word from the interface register to the AC. The
selected mode controls this transfer as indicated previously.
Skip On Transfer Request (STR) - 6753 - This instruction causes the next instruction to be skipped if
the TR flag has been set by the floppy disk drive system and clears the flag. The TR flag should be
tested prior to transferring data or address words with the XDR instruction to ensure the data or
address has been received or transferred, or after an LCD instruction to ensure the command is in the
interface register. In cases where an XDR follows an LCD, the flag only has to be tested once between
the two instructions.
Skip On Error - 6754 - This instruction causes the next instruction to be skipped if the error flag has
been set by an error condition in the floppy disk drive system and clears the flag. An error also causes
the done flag to be set.

The floppy disk drive system error status register contains the current error and status conditions of
the selected drive. This read-only register can be accessed by the read status function (101). The RXES
is also available in the interface register upon completion of any function, The RXES is accessed bv the
XDR instruction. The meaning o-f the error bits is listed in Table 13.
.I

Table 13

Error Status Register Bit Functions

Bit No.

Description

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

Parity Error - When status bit 10= 1, a parity error has been detected on command and address information being transferred to the floppy disk drive system
from the interface. Upon detection of a parity error, the current function is terminated, the RXES status word is moved to the interface register, and the error and
done flags are set. The function can be retried to determine if the parity error is a
soft or hard error. A parity error indication means that there is a problem in the
interface cable between the floppy disk drive system and the interface.

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

Deleted Data (DD) - In the course of reading data, a deleted data mark was
detected in the identification field. The data following will be collected and transferred normally, as the delet~d data mark has no further significance within the
floppy disk drive system. Any alieration of fiies or actuai deietion of data due to
this mark must be accomplished by user software. This bit will be set if a successful or unsuccessful write deleted data function is performed.

Drive Ready - This bit is asserted if the unit currently selected exists, is properly
supplied with power, has a diskette installed properly, has its door closed, and has
a diskette up to speed.

Skip On Done - 6755 - This instruction causes the next instruction to be skipped if the done flag has
been set by the floppy disk drive indicating the completion of a function or detection of an error
condition. If the done flag is set, it is cleared by the SDN instruction. This flag will interrupt if
interrupts are enabled.
Interrupt Enable (INTR) - 6756 - This instruction enables interrupts by the done flag if AC 11 = 1. It
disables interrupts if AC 11 = o.
Initialize (lNIT) - 6757 - The initialize instruction initializes the floppy disk drive by moving the head
position mechanism of drive 1 (if drive 1 is available) to track O. It reads track 1, sector 1, of drive 0, It
zeros the error and status register and sets the done flag upon successful completion of initialize. Up to
1.8 seconds can elapse before the floppy disk drive system returns to the done state.

MR78 Interface
The MR 78 interface is available for interfacing the optional MR 78 device with the VT78 terminal via
the connector on the I/O distribution panel.
The MR78 device, described in detail in the DECstation Technical Manual, contains a programmed set
of ROMs and is accessed using the lOTs listed in Table 14. Data from the MR78 is in binary paper
tape format. The data is checksummed and, if an error is encountered, it will be reported on the display
as a HLT with status information. The MR78 interface port does not provide for interrupts.

Table 14 MR78 lOTs
Octal

Mnemonic

Function

6011

RSF

Skip if a character is available.

6016

RRBRFC

OR the character presently at the port into the AC (4-11),
I1 Then
clear the character available flag, and obtain a new character.
set character available flag when next character arrives.

Serial Line Unit 1 (SLU 1)
SLU 1 is hardwired to the keyboard/video display. The lOTs associated with SLU 1 are listed in Table

15.
Table 15

SLU 1 lOTs

Octal

Mnemonic

Time (JLs)

Description

6030

KCF

Clear the input flag.

6031

KSF

Skip if input flag set.

6032

KCC

Clear input flag, clear AC.

6034

KRS

OR content of input buffer into AC.

6035

KIE

Load content of AC(lI) into interrupt enable
flip-flop.

6036

KRB

Load content of input buffer into AC, then
clear input flag.

6037

KLB

Load content of AC(ll) into loopback flipflop.
NOTE
This lOT is used for internal diagnostics. Setting the loopback flipflop disconnects all SL U s from their
connector and connects the outputs
back to the inputs of each SLU including the video terminal SL U 1.

Table 15

SLU 1 lOTs (Cont)

Octal

Mnemonic

Time (J.ls)

Description

6040

SPF

Set output flag enable.

6041

TSF

Skip if output flag is set and flag enable is set.

6042

TCF

Clear output flag enable.

6043

TSB

Set the baud rate. (See Table 16.)

6044

TLS

Same as 6046.

6045

TSK

Skip if SLU 1 interrupt enable is set and the
input flag is set; or if the SLU 1 interrupt enable flag is set and output flag enable are both
present.

6046

TLS

Load the content of AC 4-11 into the SLU
transmitter and send the character out over
the serial line. Set the output flag enable flipflop. As soon as the new character is loaded
into the transmitter, set the output flag.

Serial Line Unit 2 (SLU 2)
SLU 2 is a full-duplex EIA port with programmable baud rate selection. SLU 2 is different from the
other SLUs because it has programmable bit detection, character length, stop bit selection, and parity
generation. Error bit detection is accomplished with Kl El lOT. The remaining programmable options
are done with Kr-v1Dl lOT. The device input code of SLU 2 is 30, the output code is 31.
The lOTs associated with SLU 2 are listed in Table 17.

Table 16

Baud Rates

AC 8-11

Baud Rate

AC8-11

Baud Rate

0
1
2
3
4

50
75
110*
134.5
150*
300*
600*

10
11
12
13
14
15
16

1800
2000
2400*
3600
4800*
7200
9600*

1200*

19200

5
6
7

*Available preselect switch settings for SLU 2.

Table 17 SLU 2 lOTs
Octal

Mnemonic

Description

6300

KCFl

Clear input flag.

6301

KSFI

Skip if input flag is set.

6302

KCC1

Clear input flag, clear AC.

6304

KRS1

OR contents of input buffer into AC.

6305

KIEI

Load content of ACI0 into status enable flip-flop and load
contents of AC 11 into interrupt enable flip-flop. (See Table
18.)

6306

KRBI

Load contents of input buffer into AC, then clear input flag.

6307

KMD1

Set the operating mode of SLU 2. (See Table 19.)

6310

SPF1

Set output flag enable.

6311

TSF1

Skip if output flag is set and flag enable is set.

6312

TCF1

Clear output flag enable.

6313

TSBi

Set baud rate according to Table 16. I'-~ ormally, this instruction is preceded by an LAS instruction, which obtains a bit
pattern from the rotary switch on the I/0 distribution panel.

6303

This lOT is the same as 6316 (TLS 1).

6314
6315

TSKI

Skip if SLU 2 interupt enable is set and if the input flag is set
or if the output flag and output flag enable are both present.

6316

TLSI

Load the contents of AC 4-11 into the SLU transmitter and
send the character over the serial EIA line. As soon as a new
character is loaded into transmitter set output flag.

Table 18 Loading Contents of AC Into Status
Enable and Interrupt Enable Flip-Flops
AC Bit

Function

ACIO

If AC(lO) = 1, dudng KIEI lOT, error bits are enabled and four extra bits are read
into the AC along with the incoming character. These are:
ACO

Set if any error exists.

ACI

Set if parity error has occurred.

AC2

Set if framing error has occurred. A framing error is caused by an invalid stop
bit and usually signifies either a break character has been transmitted or the
incoming line is open.

AC3

Set if overrun error has occurred. An overrun error occurs when a new character arrives before the last one was serviced by the program.

Table 19
AC Bit

Setting SLU 2 Operating Modes

Function
NOTE
If the A C bits defined in this table are set, the associated functions will be performed (SLU 2 only) with
the KMDI lOT.

If AC(7) = 0, generate and check parity
If AC(7) = 1, inhibit parity generation and checking and clear parity error bit.

If AC(8) = 0, select 1 stop bit.
If AC(8) = 1, select 1.5 stop bits for a 5-element character. Select 2.0 stop bits for all
other lengths.

9, 10

Select number of elements per character length.
9

10 Elements per character
0
5
016

o
1
1
11

°
1

7
8

If AC 11 = and AC 7 = 0, generate and check for odd parity. If AC 11 = 1 and AC 7
= 0, generate and check for even parity.

Serial Line Unit 3 (SLU 3)
SLU 3 has a programmable baud rate, but is hardwired for 8-bit words. It has no parity or error
detection capabilities and is always operated in the full-duplex mode.
The lOTs associated with SLU 3 are listed in Table 20.

Table 20
,-

SLU 3 lOTs

Description

Octal

Mnemonic

6320

KCF2

Clear input flag.

6321

KSF2

Skip if input flag is set.

6322

KCC2

Clear input flag and clear AC.

6324

KRS2

OR content of input buffer into AC.

6325

KIE2

Load contents of AC(11) into interrupt enable flip-flop.

6326

KRB2

Load contents of input buffer into AC then clear input flag.

6330

SPF2

Set output flag enable.

6331

TSF2

Skip if output flag is set and flag enable is set.

6332

TCF2

Clear output flag enable.

6333

TSB2

Set baud rate according to Table 16.

6323

Same as 6336 (TLS2).

6334
6335

TSK2

Skip if SLU3 interrupt enable is set and the input flag is set or
the output flag and output flag enable are both present.

6336

TLS2

Load the contents of AC 4-11 into the SLU transmitter and
send the character over the serial EIA line. As soon as a new
character can be loaded into the SLU transmitter, set the output flag.

Parallel I/O
The parallel I/O permits 12-bit data to be transferred between the processor accumulator and peripheral devices. It has 12 bidirectional lines. Two device codes are availabie for this interface - device code
66 and 50. The choice between device codes is made by the logic level present at one pin of the parallel
I/O connector. Device code 66 is generally used to generate LA 78 printer lOTs. Device code 50 is used
for the LQP78 printer. The parallel I/O may also be used as a general-purpose 12-bit parallel I/O port
using either set of lOT instructions and the signal line OUT to allow input of externally supplied data.
The paralle~ I/O lOTs for the LA 78 printer and the LQP78 printer are listed and described in Tables
21 and 22, respectively.
44

Table 21

Parallel lOTs - LA78 Printer

Octal

Mnemonic

Time (;.Ls)

Description

6660

PSSF

Set the print flag (AC unchanged).

6661

PSKF

Skip on flag (if the character RDY flag is set
the next sequential instruction is skipped).

6662

PCLF

Clear flag (the character RDY flags are
cleared - AC not changed. Status register not
affected).

Not used.

6663
6664

PSTB

Load printer buffer. AC (0: 11) are transferred
to the interface buffer register. Approximately
200 ns later, character strobe is issued. AC is
not changed.

6665

PCIE

Set or clear interrupt enable* if ACll(O) interrupt enable is cleared. If ACII(1) interrupt
enable is set, AC is not changed.

6666

PCLF PSTB

Load buffer and clear flags (combination
6664 and 6662).

6667

PRDB

Read data. If the OUT line is high, the contents of the previous buffer load (6664 or
6666) are read back into the AC. If OUT is
low, a I2-bit word supplied by the external
device is loaded into the AC,

*After CAF or power on interrupts are enabled.

Table 22

Parallel lOTs - LQP78 Printer

Octal

Mnemonic

Time (j.Ls)

Description

6500

LQSK

Skip on done flag. If any of the following conditions exist, skip the next instruction: the
transition from high to low of "character
ready," "paper ready," "carriage ready,"
"printer ready," or the "check" line has taken
place since this lOT was last issued.

6501

LQRB

Read buffer if the OUT line is high. The contents of the output register are read back into
the AC. If the OUT line is low, a 12-bit word
supplied by the external device is read into the
AC.

Table 22

Parallel lOTs - LQP78 Printer (Cont)
Time (~s)

Octal

Mnemonic

6502

LQMP

Move paper. AC (0: 11) are sent to the output
register and, 200 ns later, a "paper strobe"
pulse is issued. The AC and the paper ready
flag are cleared.

6503

LQMC

Move carriage. AC (0: 11) are sent to the output register and, 200 ns later, a "carriage
strobe" pulse is issued. The AC and the carriage ready flag are cleared.

6504

LQPC

Print a character. AC (0: 11) are sent to the
output register and, 200 ns later, a "character
strobe" is issued. The AC and the character
ready flag are cleared.

6505

LQRS

Read status and clear done flag. The state of
the lines listed below are stored in the AC,
then the done flag is cleared.

Description

ACO = 1 Printer Ready
1 = Character Ready
2 = Carriage Ready
3 = Paper Ready
4 =0

5=0

6 = Check
AC 7
=0
o _ ()
Ar"-

fi\""'-

o -

AC 9 = 0
AC 10 = Lift ribbon
AC 11 = Interrupt enable
6506

LQLS

Write status and set done. AC (10:11) are sent
to the interface to set or clear certain control
bits

AC 10(1) - Set lift ribbon
A C 10(0) - Clears lift ribbon
AC 11(1) - Sets interrupt enable*
AC 11(0) - Clears interrupt enable.
6507

LQRE

Restore and clear done flag. Restore strobe is
issued for approximately 200 ns. The done
flag is cleared. AC is not affected.

*After CAF and power up, interrupts are disabled.

KEYBOARD/VIDEO DISPLAY
The keyboard/video display (Figure 20) enables the user to communicate with the processor and
control all of the system peripheral devices,

KEYBOARD!VIDEO DISPLAY

VIDEO
DIS?LAY

•

VIDEO
MEMORY&
CONTROL

KEYBOARD

SLU1

I I

I
PROCESSOR

1
08-1931

Figure 20

Keyboard/Video Display Block Diagram

The keyboard/video display features full-duplex operation with 8-bit ASCII characters. These characters are transmitted or received as seriai data coded with a start bit, eight data bits, and a stop bit.
The keyboard/video display is hard-wired to SLU 1 (part of the processor), which provides the interface between the keyboard/video display and the processor.
Keyboard
The keyboard transmits codes to the processor using a set of I/O transfer instructions (device code 03).
Some keyboard keys transmit one or more codes to the processor when typed. Others, such as the shift
key, are control keys and send no codes.

The code transmitting keys cause the keyboard/video display to make a clicking sound to verify that a
keystroke has been sent to the processor. The code is transmitted in the order that the keys are pressed.
If three keys are pressed simultaneously, the first two key codes will be transmitted immediately but
the third will not be transmitted until the first two keys are released.
All alphabetic keys transmit in uppercase and lowercase code. Uppercase is transmitted when a key is
typed while the SHIFT or the CAPS LOCK key is down. (The CAPS LOCK key does not affect codes
transmitted by keys other than the alphabetic keys). The uppercase and lowercase key codes are listed
in Table 23.
The numeric and symbol key codes are listed in Table 24.

Table 23
Key

A
B

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

Q
R
S

Alphabetic Key Codes

Uppercase
Code*

Lowercase
Code*

101
102
103
104
105
106
107
110

141
142
143
144
145
146

111

151

112
113
114
115
116
117
120
121
122

152
153
154
155
156
157
160
161
162
163
164
165
166
167
170
171
172

147

150

123

124
125
126
127
130
131
132

T
U
V
W
X
Y

*All codes are expressed in octal. Note that there are no 8s or 9s in the octal system.
Table 24
Key

2
3
4

5
6
7
8
9

o
=

Numeric/Symbol Key Codes

Neither SHIFf
Key Down

Either or Both
SHIFf Keys Down

061
062
063
064
065
066
067
070
071
060

041 (!)
100 (@)
044 ($)
045 (%)
136 (A)
046 (&)
052 (*)
050(0
0510)

055

1,) I ~_)

075
133

053 (+)

043 (#)

1 . , ' " I'

135 (D
072 (:)
042 (")

073
047

054
056

074

«)

076 (»
077 (?)

057

The function keys transmit control codes to the processor. They cause an action to occur in the
keyboard/video display such as tab, line feed, etc., if the processor echos these codes back to the
keyboard/video display.
The CTRL key is used in conjunction with other keys on the keyboard to produce control codes in the
range of 000-037. When held down it alters the code normally produced by a typed key by forcing the
two high-order bits of the code to zero. Table 25 lists the codes transmitted when the control key is
held down. The original code is included for comparison.

Table 25
Code Originally
Transmitted
040 or 100 or i40
041 or 101 or 141
042 or 102 or 142
043 or 103 or 143
044 or 104 or 144
045 or 105 or 145
046 or 106 or 146
047 or 107 or 147
050 or 110 or 150
051 or 111 or 151
052 or 112 or 152
053 or 113 or 153
054 or 114 or 154
055 or 115 or 155
056 or 116 or 156
057 or 117 or 157
060 or 120 or 160
061 or 121 or i6i
062 or 122 or 162
063 or 123 or 163
064 or 124 or 164
065 or 125 or 165
066 or 126 or 166
067 or 127 or 167
070 or 130 or 170
071 or 131 or 171
072 or 132 or 172
073 or 133 or 173
074 or 134 or 174
075 or 135 or 175
076 or 136 or 176
077 or 137 or 177

Control Key Codes
With The CTRL Key Down
Code Actually
Special
Transmitted
Name
000
001
002
003
004
005
006
007
010
011
012
013
014
015

NTTT
1 UL
SOH
STX
ETX
EOT
ENQ
ACK
BELL
BS
HT
LF
VT
FF
CR

{\1~

~()
u'-'

017
020
02i
022
023
024
025
026
027
030
031
032
033
034
035
036
037

SI
DLE
DClorXON
DC2
DC30rXOFF
DC4
NAK
SYN
ETB
CAN
EM
SUB
ESC

VIV

as
RS
US

The ESC key is used to select a command rather than the characters noted on the character keys. For
example, if the keyboard/video display receives code 102, it will display a B on the video screen. If it
receives 033, or the ESC key is pressed when the letter B is typed, the code preceding 102 will initiate a
command rather than display the character. The letter B will not be displayed on the video screen. If a
control code is sent to the keyboard/video display between the ESC and the final character, the function specified by the control code will be performed when the control code is received. The function
specified by the escape sequence will be performed when the final character is received.
If the keyboard/video display receives ESC ESC from the processor, the second ESC will not cancel
the escape sequence, but will continue to be ready to interrupt the next character in the escape
sequence.
Typing the BREAK key forces the serial data output line of the keyboard/video display to the zero
state for as long as the key is held down. The BREAK function is provided for users with software
written to operate in the half-duplex mode. The keyboard/video display normally operates in the fullduplex mode so there is usually no need for the BREAK function.
The 19-key auxiliary keypad is provided for applications requiring heavy use of the numeric keys. In
addition to the 10 numeric keys, the keypad has a decimal point key, four cursor move keys, three
blank keys, and an ENTER key.
In the normal mode of operation, the decimal point key and the numeric keys transmit the same code
as the decimai point key and the numeric keys on the main keyboard. The processor cannot distinguish
between them. The ENTER key transmits the same code as the RETURN key.
In response to a command from the processor, the keyboard/video display will enter the alternatekeypad mode and the ENTER, decimal point, and numeric keys will each transmit a unique escape
sequence. This allows the processor to distinguish between main keyboard entries and auxiliary keypad entiies. It also provides the processor with 12 user-definable keys to use for individual applications. Table 26 lists the codes transmitted by these keys.

Table 26

Key

o
1
2
3

4
5
6
7
8
9

ENTER

Keypad Numeric Key Codes

Code( s) Transmitted To Processor
Key Not in AlternateAlternate-Keypad Mode
Keypad Mode
030077 160 (ESC? p)
033077161 (ESC? q)
033077162 (ESC? r)
033077 163 (ESC? s)
033 077 164 (ESC? t)
033077 165 (ESC? u)
033077 166 (ESC? v)
033 077 167 (ESC? w)
033 077 170 (ESC? x)
033077 171 (ESC? y)
033 077 156 (ESC? n)
033077 115 (ESC? M)

060
061
062
063
064
065
066
067
070
071
056
015

Note: None of the keys on the auxiliary keypad are affected by pressing the SHIFT, CAPS LOCK, or CTRL
keys.

The seven remaining keys on the keypad are the four cursor move keys and three blank keys. The
cursor move keys transmit an escape sequence to the processor. If the processor echos these codes back
to the keyboard/video display, the cursor will move one character position up, down, left, or right,
depending on the typed key. The three blank keys transmit user-defined escape sequences. The user
can define the meaning of each key to fit a particular application. Table 27 lists the codes transmitted
by these seven keys.

Table 27

Keypad Control Key Codes

Keypad Key

Code(s) Transmitted to
Processor

Left blank key
Center blank key
Right blank key
Up-arrow key
Down-arrow key
Right-arrow key
Left-arrow key

033 120 (ESC P)
033 121 (ESC Q)
033 122 (ESC R)
1 rr.s"",
1"\"'3
v.) 110 1~.c
\..... A)
033 102 (ESC B)
033 103 (ESC C)
033 104 (ESC D)

None of the keys on the auxiliary keypad are affected by pressing the SHIFT, CAPS LOCK, or CTRL
keys.
The REPEAT key is used in conjunction with other keys. It does not transmit a code. Any key that
transmits a code to the processor will transmit that code repeatedly if pressed while the REPEAT key
is down.
The SCROLL key also performs a local function. It is used to request more data from the processor
when the keyboard/video display is in the hold screen mode. Typing SCROLL will add one line of
characters to the display screen. Typing SHIFT SCROLL will add a screenful of characters.
The COpy key is employed only when using the optional copier peripheral device.
Table 28 lists the function keys, their code, and the keyboard/video display action taken if the code is
echoed back to the keyboard/video display.
Display
The display portion of the keyboard/video display has no programmable features. Refer to the DECstation Technical Manual for a detailed functional desciption of the display portion of the keyboard/video display.
Basic Cursor Movement Commands
Line Feed (LF - 012) - The LF command moves the cursor down one character position to the same
column of the line below. If the cursor was on the bottom line of the screen to begin with, it wili remain
where it was, but all of the information on the screen will move up one line. The information previously on the top line will be lost from the screen and a new bottom line will appear. This process is
referred to as an upward scroll.

Table 28

Function Key Codes

I Action

Key

Code Sent

RETURN

015

Carriage Return function.

LINE FEED

012

Line Feed function.

BACKSPACE

010

Backspace (Cursor Left) function.

TAB

011

Tab function.

Space bar

040

Deposit a space on the screen, erasipg what was there before.

DELETE

177

Nothing.

ESC (SEL)

033

Interpret the next character from the processor as a command, rather than displaying it.

Cursor Down (ESC B - 033 102) - This command moves the cursor in the same manner as the LF
command. If the cursor was on the bottom line of the screen to begin with, it will remain where it was,
and no scroll will occur.
Reverse Line Feed (ESC 1 - 033 111) - The reverse line feed command moves the cursor up one
character position to the same column of the line above. If the cursor was on the top line to begin with,
it will remain where it was, but all of the information on the screen will move down one line. The
information that was previously on the bottom line of the screen will be lost and a new blank line will
appear at the top line. This process is referred to as a downward scroll.
Cursor Up (ESC A - 033 1(1) - The cursor up command moves the cursor up one character position to
the same column of the line above. If the cursor was on the top line to begin with, it will remain where
it was, and no scroll will occur.
Space (040) - The space command erases the character at the cursor position and the cursor moves one
column to the right. If the cursor was at the end of the line to begin with, it will not move.
Space can be viewed as a command to erase one character or simply as a displayable character.
Programs written for teleprinters that position the carriage (or cursor) by returning it to the left of the
line and spacing it over to the desired column may have to be rewritten. The cursor right command
should be used instead of space to move the cursor to a certain column, over data that has already been
written on the screen.
Cursor Right (ESC C - 033 103) - This command causes the cursor to move one column to the right. If
the cursor was at the end of the line to begin with, it will not move. No character on the screen will be
erased.

Cursor Left or Backspace (BS 010) or (ESC D - 033 104) - This command moves the cursor one
column to the left. If the cursor was at the start of the line to begin with, it will not move. No character
on the screen will be erased.
NOTE
Even though the keyboard/video display responds to
the backspace code it is impossible to produce a composite character on the screen by backspacing and
overprinting one character on another. If this is
attempted, the overprinted character will vanish from
the screen because only one character can occupy a
character position at any time.
Advanced Cursor Movement Commands
Carriage Return (CR 015) - The carriage return command moves the cursor to the start (leftmost
column) of the line it was in. If it was there to begin with, it will remain there.
Cursor Home (ESC H - 033 110) - This command moves the cursor to the home position (the character position at the upper left corner of the screen). If the cursor was there to begin with, it will remain
there.
TAB (TAB 011) - The tab command moves the cursor to the right until it reaches a horizontal tab stop.
The cursor remains in the same line it was in. If columns are numbered from 1 (leftmost column) to 80
(rightmost column), the TAB stops will be fixed in columns 9, 17, 25, 33, 41, 49, 57, 65, and 73. If the
cursor was at a tab stop to begin with, it will move right to the next tab stop. If the cursor was in
columns 73-79, it will move right one column. If the cursor was in column 80, it will not move.

Direct Cursor Addressing (ESC Y - 033 131) - The next code after ESC Y that the processor sends to
the keyboard/video display will not be displayed but will be interpreted as specifying one of the lines
on the screen. The character the keyboard/video display receives after that will not be displayed but
will be interpreted as specifying one of the columns on the screen. The cursor will be moved to the
character Dosition at the soecified Hne and coiumn. The comoiete direct cursor addressinl! command
has the fo;m ESC Y line #Acolumn # and consists of four charitcters from the processor. C;ntrol codes
or other escape sequences should not be embedded in this string of four characters. Doing so will
produce unspecified results.
For line #, the processor sends octal code 040 to specify the top line of the screen, 041 to specify the line
below the top line, and so forth. Octal code 067 specifies the bottom line. If line # does not specify a
line that exists on the screen, the keyboard/video display will not move the cursor vertically if the
vertical parameter is out of bounds. A direct cursor addressing command with the first parameter
greater than 067 can be issued to the keyboard/video display to move the cursor arbitrarily in the
horizontal direction without the flickering of the video that the direct cursor addressing command can
cause.
For column #, the processor sends octal code 040 to specify the leftmost column in a line and 157 to
specify the rightmost column. If column # is greater than 157 and does not specify a column that exists
on the screen, the cursor will be moved to the rightmost column.
Screen Erasure Commands

Erase To End-Of-Line ((ESC K - 033 113) - This command erases all of the information at the cursor
position and rightward to the end of the line. Spaces are deposited at those character positions. If the
cursor is at the rightmost column of a line, the character at the cursor position will be the only
character to be erased. If the cursor is at the leftmost column of a line, the entire line will be erased.
53

Erase To End-Of-Screen (ESC J - 033 i12) - This command erases all of the information from the
cursor position to the end of the screen. The erase to end-of-screen command does what the erase to
end-of-line command does and also erases the information in every line below the cursor. If the cursor
is at the lower right corner of the screen, one character will be erased. If the cursor is at the home
position of the screen, all of the information on the screen will be erased.
In addition to the screen erasure commands, the space command can be thought of as a single-character screen erasure command.
Hold-Screen Mode of Operation
The hold-screen mode of operation allows the operator to control the rate at which data enters and
leaves the screen. This is important because the keyboard/video display can operate at such fast speeds
that data from the processor might remain on the screen for only a few seconds before it scrolls up and
off the top of the screen to make way for new data.
Whenever the keyboard/video display cannot process data from the processor, it automatically transmits control code XOFF (023). When it is ready again it transmits XON (021). The keyboard/video
display depends on the processor to suspend its transmission promptly when the processor receives
XOFF from the keyboard/video display and resumes transmission where it left off upon receiving
XON. When software places the keyboard/video display in the hold-screen mode of operation, the
keyboard/video display will refuse to perform scrolls. If the processor commands the display to scroll
by sending the keyboard/video display a LF (012) when the cursor is on the bottom line, the keyboard/video display will place the LF in a silo (first in, first out memory) to be executed later, and send
XOFF to the processor. XOFF means the keyboard/video display is not ready for more data from the
processor because the keyboard/video display assumes that the operator is not ready for more.
The SCROLL key is pressed when the operator wants to see more data. The keyboard/video display
then processes the LF character out of the silo. When this happens a scroll occurs. The keyboard/video display then takes any other characters from the silo that may have arrived from the
processor before the processor responded to the XOFF and suspended its output. Each character in
the silo is displayed on the screen or, in the case of commands, executed exactly as if it had just been
received - unless it is another LF causing another scroll. If the keyboard/video display encounters an
LF in the silo, it will stop processing characters out of the siio untii the operator types the SCROLL
key again.

If the keyboard/video display processes all the characters in the silo without finding an LF, it will
transmit XON to the processor to notify it that the keyboard/video display is again ready to receive
characters. It will display all the characters and execute all the commands until it is again ordered to
perform a scroll. Then it will send XOFF, store the LF in the silo, and wait for the operator to press
the seRO LL key again.
If the processor ignores the XOFF signal, it might completely fill the silo. Then, rather than allow data
to be lost, the keyboard/video display will perform the scroll it was commanded to perform despite the
hold-screen mode. It will remove the characters from the silo and interpret them, reducing the backlog.
However, the keyboard/video display will not exit hold-screen mode.
The SCROLL key is typed to request that another line be admitted to the screen. The keyboard/video
display translates this request into start and stop commands (XON and XOFF) and sends them to the
processor in such a manner that just enough data comes to the keyboard/video display to satisfy the
operator's request for one more line.
The operator can type the SCROLL key with the SHIFT key down to request a new screenful of data.
As with the unshifted SCROLL request, the keyboard/video display begins to process characters again
and sends XON to the processor when the characters that accumulated in the silo have all been
processed. But the shifted scroll request tells the keyboard/video display to allow an entire screenful of
new data to enter the screen before shutting off the transmission from the processor.

Enter Hold-Screen Mode (ESC - 033 133) - When the keyboard/video display enters hold-screen
mode, data will not be allowed to scroll off the screen without permission from the operator by use of
the SCROLL key. After entering the hold-screen mode, the first command that would cause a scroll to
occur will not be processed immediately, and the keyboard/video display will send XOFF to the
processor.
The hold-screen mode will remain in effect until the exit hold-screen mode command disables that
feature.
Exit Hold-Screen Mode (ESC / - 033 134) - When the keyboard/video display exits the hold-screen
mode, data will be allowed to scroll off the screen if it has to to make room for new data coming from
the processor.
Alternate-Keypad Mode Of Operation
The auxiliary keypad is capable of transmitting the codes listed in Table 26. There are two sets of codes
that the software can select by issuing these commands - enter alternate-keypad mode and exit alternate-keypad mode.
Alternate-Keypad Mode (ESC = - 033 075) - The alternate-keypad mode enables the numeric keys,
decimai point key, and ENTER key to transmit unique escape sequences, aliowing software to distinguish between them and keys on the main keyboard, and to assign its own meaning to each key.
The alternate-keypad mode will not be in effect until the processor issues this command. Once enabled,
it will remain in effect until the processor uses the exit alternate-keypad mode instruction.
Exit Alternate-Keypad Mode (ESC) - 033 076) - When the exit alternate-keypad mode is initiated the
numeral, decimal point, and ENTER keys transmit codes are indistinguishable from the codes transmitted by the numeric, decimal point, and RETURN keys on the main keyboard. Applications that do
not need to redefine the meanings of these twelve keys will work correctly allowing the operator to use
the keypad for entry of numeric data.
Graohics Mode Of Operation
The~e are 33 special s&ymbols that can be displayed on the screen of the keyboard/video display. These
symbols can be entered on the screen only by placing the keyboard/video display in the graphics mode.
Normally, codes 136-176 stand for lowercase letters and symbols. In the graphics mode, each code in
this range will specify that one of the special symbols be placed on the screen. Table 29 describes the
appearance of the keyboard/video display special symbols that are displayed on the screen in the
graphics mode.
Codes 040-135 are unaffected. The symbols represented can be placed on the screen whether or not the
keyboard/video display is in the graphics mode.
The keyboard/video display uses the control codes to mark the position of the special symbols in its
memory. Therefore, the special symbols and the lowercase letters can coexist on the screen. The special
symbols will remain on the screen where they were entered even if the keyboard/video display is taken
out of the graphics mode.
Enter Graphics Mode (ESC F - 033 106) - This command causes codes 136-176 to be converted to
spe--cial symbols before being placed on the screen. This remains true until the keyboard/video display
receives the exit graphics mode command.
Exit Graphics Mode (ESC G - 033 107) - The exit graphics mode signal causes codes 136-176 to
resume their standard (ASCII) meanings.

Table 29

Graphic Mode Symbols
The Screen Will Display

When This Code
Received

In Graphics
Mode

Not In
Graphics Mode

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

blank
blank
reserved
solid rectangle
1/
3/
5/
7/
degrees
plus or minus
right arrow
ellipsis
divide by
down arrow
bar at scan 0
bar at scan 1
bar at scan 2
bar at scan 3
bar at scan 4
bar at scan 5
bar at scan 6
bar at scan 7
subscript 0
subscript 1
subscript 2
subscript 3
subscript 4
SUbscript 5
subscript 6
subscript 7
subscript 8
subscript 9
paragraph

It;:7
J.VI

170
171
172
173
174
175
176

a
b
c
d
e
f
g
h
J

k
I
m
n
0

p
q
r
s
t
u
v
w
x

z
C

)

Uses of Special Symbols
Codes 154-163 - These codes cause eight horizontal lines at various scans within the character positon
to be displayed. These bars can be used to print a bargraph on the screen with more accuracy than
would be possible using only minus signs and underlines.
Codes 142-154 - (1/,3/,5/, and 7/) are used preceding the subscripts to form fractions. In particular,
the fractions 1/8, 1/4, 3/8, 1/2, 5/8, 3/4, and 7/8 can be formed using these four symbols and the
subscripts.
Code 151 - The ellipsis appears as three dots in the character position C••• ). The spacing of these three
dots is such that several of these symbols placed adjacent to one another in the screen will produce a
smooth line of dots.
Codes 136-140 - These codes are reserved for future use.
56

APPENDIX A
OPERATING AND ENVIRONMENTAL SPECIFICATIONS

DECstation with MR78
Operating Environment:
Temperature
Relative humidity
Maximum wet bulb
Minimum dew point

10-40 0 C (50 0 - 104 0 F)
10 to 90 percent
28 0 C (82 0 F)
2 0 C (36 0 F)

Line voltage

95-127 V or 190-254 V

Line frequency

47-63 Hz-

DECstation with RX78 Floppy Disk Drive System
Operating environment:
Temperature
10-32 0 C (59 0 - 90 0 F)
Relative humidity
20 to 80 percen t
25 0 C (77 0 F)
Maximum wet bulb
Minimum dew point
2 0 C (36 0 F)
Line Voltage

95-127 V or 190-254 V

Line Frequency

50 ± 1 Hz or 60 ± 1 Hz

APPENDIX B
CARE AND HANDLING OF DISKETTES

To prolong the diskette life and prevent errors when recording or reading, reasonable care should be
taken when handling the diskette. The following handling recommendations should be followed to
pre"/ent unnecessary loss of data or interruptions of system operation.
1.

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

Paper clips shouid not be used on the diskette.

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

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

Do not attempt to clean the diskette in any manner.

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

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

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

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

10.

Do not place heavy items on the diskette.

11.

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

12. If a diskette has been exposed to temperatures outside of the operating range, allow five

minutes for thermal stabilization before use. The diskette should be removed from its envelope during this time.
13. Store diskettes horizontally, in piles of ten or less. If vertical storage is necessary, the diskettes should be supported so that they do not lean or sag, but should not be sUbjected to
compressive forces. Permanent deformation may result from improper storage.
14.

Diskettes should be stored in their original shipping containers when not in use.

APPENDIX C
CONTROLS AND INDICATORS

This appendix contains a list of the DECstation operator's controls and indicators.
NOTE
There are no floppy disk operator's controls or
indicators.
VT78 Terminal
All of the VT78 terminal operator controls, with the exception of the terminal ON/OFF and START
switches, are located on the keyboard. The terminal ON/OFF switch is located at the rear of the
terminal. The START switch is located on the terminal's side.

The keyboard (Figure C-l) is divided into two functional sections - the main keyboard and the auxiliary keypad. The main keyboard is arranged in the same manner as a conventional typewriter keyboard to select uppercase and lowercase alphabetic characters, numerals, and symbols. Table C-I lists
all of the keyboard controls and includes a brief functional description of each.

Figure C-I

VT78 Terminal Keyboard

Table C-l VT78 Terminal Keyboard
Controls and Indicators
Key

Function

A through Z

Selects corresponding character (uppercase or lowercase depending on position of SHIFT key) to be entered into the processor.

1 through 0
and symbol
keys (!, @, #, etc.)

Selects corresponding numeral or symbol (depending on position of SHIFT
key) to be entered into the processor.

ESC(SEL)

Interprets next character received from processor as a command.

TAB

Advances cursor to preselected tab stops.

CTRL

U sed in conjunction with other keys on the keyboard to generate control
codes.

SCROLL

U sed to request more lines when terminal is in hold screen mode of operation. Also used in conjunction with SHIFT key to view another screenful of
information.

CAPS LOCK

Causes the letters A-Z to always be uppercase characters. (CAPS LOCK
does not have any effect on numeral or symbol keys).

SHIFT

Selects uppercase or lowercase alphabetic characters and numeral or symbol
characters to be entered into the processor.

BACK SPACE

Moves cursor back one space.

LINE FEED

DELETE

Eliminates character above cursor.

RETURN

Moves cursor to extreme left margin.

REPEAT

U sed in conjunction with other keys to repeat transmission of character
selected.

COpy

Not used.

Intensity
(of terminal)

Adjusts intensity of CRT display.

nrons
return the carriatZe
to left martZin).
- -- r - the
--- - cursor
- - - - - one
-- - line
---- - (does
,,-- - not
-- ........
_
,

The auxiliary keypad is employed for applications requiring heavy use of number keys. It also contains
several cursor control keys. Table C-2 lists all of the auxiliary keys and their functions,
A more detailed description of the main keyboard and auxiliary keypad keys and the codes transmitted
when each key is pressed can be found in the programming section.
The VT78 terminal also contains controls used to select baud rates, parity, etc. These controls are not
operator controls and are set during system installation.

Tabie C-2

VT78 Terminal Auxiliary Keypad
Controls and Indicators

Key

0-9

Selects corresponding numeral to be entered into the processor and displayed
on the video screen.
Decimal point.

Et.J"TER

Cap function as the RETURN key or, in alternate-keypad mode, to transmit
unIque escape sequences.

Moves cursor one character position up, down, left, or right.
Blank keys

User-defined escape sequence application keys.

.
LA 78 Printer
The controls used to operate the LA 78 printer are shown in Figure C-2. A brief functional description
of each is listed in Table C-3. Refer to the LA 180 Maintenance Manual for a description of the paper
loading and adjustment controls.

Table C-3

LA 78 Operator Controls and Indicators

Control

TOP OF FORlvi

I Advances the paper to the top of the form. Only active when the ON

Function
LINE/OFF LINE switch is in the OFF LINE position.

ON LINE/OFF LINE Selects on line or off line mode of operation. (Normally maintained in the
ON LINE position unless operating TOP OF FORM switch.)
POWER ON/OFF
SWITCH

Controls prime power application to the printer. (Normally left in ON position.)
NOTE
There are three different audible alarm signals in the
LA 78 - a continuous tone indicates a carriage jam or
failure, repetitive beeping indicates an out of paper
condition or a bell code, a single beep indicates a bell
tone. If any of these signals occur during operation,
perform the remedial actions specified in the LA 78
Maintenance lVianual.

Figure C-2

LA 78 Printer Operator Controls

LQP-78 Printer
The LQP-78 printer operator controls are shown in Figure C-3. Table C-4 lists all of the operator
controls and includes a brief functionai description of each.

Refer to the LQP78 Maintenance Manual for a description of the paper loading and adjustment controls.
Table C-4

LQP78 Printer Operator Controls and Indicators

Control/Indicator

Function

PAUSE

Pressed to suspend printer operation. Printer operation is resumed when
switch is pressed a second time.

PRINTER READY

Illuminates when prime power is applied to the printer and the printer is
ready for operation.

END OF RIBBON

Illuminates when the end of the carbon ribbon is reached.

Figure C-3

LQP78 Printer Operator Controls

DECSTATION
USER'S GUIDE
EK-VTX78-UG-OOl

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