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DEC-11-HLCA-D

December 1971

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Document:	LC11 DECwriter system engieering drawings MISSING ONE PAGE Oct1971
Order Number:	DEC-11-HLCA-D
Revision:	000
Pages:	26
Original Filename:	http://bitsavers.org/pdf/dec/unibus/DEC-11-HLCA-D_LC11_DECwriter_system_manual_Dec1971.pdf

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LC11
DECwriter system
manual

(

DEC-II-HLCA-D

LC11
DECwriter system
manual

(
DIGITAL EQUIPMENT CORPORATION

MAYNARD, MASSACHUSETTS

1st Edition December 1971

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

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

DEC
FLIP CHIP
DIGITAL
UNIBUS

PDP
FOCAL
COMPUTER LAB

CONTENTS

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ILLUSTRATIONS
Page

CHAPTER 1 INTRODUCTION
1.1
1.2
1.3
1.4
1.5
1.6

Introduction
Scope
Specifications
Maintenance
Engineering Drawings
Terminology

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

Figure No.
2-1
3-1
3-2
4-1
4-2
4-3
4-4
5-1

Title

Art No.

Page

LCl1 Controller-Simplified Block Diagram
DECwriter Controls and Indicators
Loading Paper into LA30 DECwriter
Keyboard Status Register-Bit Assignments
Keyboard Data Buffer Register-Bit Assignments
Printer Status Register-Bit Assignments
Printer Data Buffer Register-Bit Assignments
Interface Signals

11-0670
11-0671
11-0672
11-0673
11-0674
11-0675
11-0676
11-0678

2-2
3-1
3-2
4-1
4-2
4-2
4-2
5-3

CHAPTER 2 GENERAL DESCRIPTION
2.1
2.2
2.3

Introduction
DECwriter
LC 11 Controller

2-1
2-1
2-1

CHAPTER 3 OPERATION

/'~

(

3.1
3.2
3.3
3.4

Introduction
Controls and Indicators
Keyboard
Loading Paper

CHAPTER 4

PROGRAMMING INFORMATION

4.1
4.2
4.3
4.4
4.5
4.6

Scope
Device Registers
'Interrupts
Timing Considerations
Programming Note
Programming Examples

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

CHAPTER 5 THEORY OF OPERATION
5.1
5.2
5.3
5.4

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

5.5
5.6

Introduction
Selection Logic
Interrupt Control
Keyboard Logic
Printer Logic
Interface Signals

APPENDIX A CHARACTER CODES

5-1
5-1
5-1
5-2
5-3
5-3
A-I

TABLES
Table No.
1-1
1-2
1-3
2-1
3-1
4-1
5-1
5-2
5-3

Title

Page

Applicable Documents
LCll Controller Specifications
LA30 DECwriter Specifications
DECwriter Models
Controls and Indicators
Standard Device Register Assignments
Gating and Select Line Signals
Controller-DECwriter Interface Signals
Controller Input/Output Signals

1-1
1-2
1-2
2-1
3-2
4-1
5-2
5-4
5-4

)

CHAPTER 1
INTRODUCTION

Table 1-1
Applicable Documents

1.1 INTRODUCTION

The LCn DECwriter System is a high-speed teletypewriter system designed to interface with the PDP-ll family of processors to provide both input (keyboard) and output
(printer) functions for the system. The system can receive ch~racters from the
keyboard or can print at speeds up to 30 characters per second In standard ASCII
formats. The LCn System consists of two distinct components: an LA30 DECwriter and
a DEC PDP-ll interface unit, which is referred to as the LCn Controller.
LA30 DECwriter

Number

Coverage

Unibus Interface Manual,
Second Edition

DEC-I1-HIAB-D

Provides detailed theory, flow, and logic
descriptions of the Unibus and external device logic. Includes detailed discussions of
the following modules used in the LC 11
Controller:
MI05 Address Selector
M782 Interrupt Control

PDP-ll/20 System*
(7 -volume series)

DEC-U-HRIB-D
through
DEC-II-HR7B-D

Provides detailed theory of operation, flow,
logic diagrams, operation, installation, and
maintenance for components of the PDP-11
System including processor, memory, console, and power supply.

PDP-II Handbook

Second Edition,
1970

A general handbook that provides discussions of addressing modes, the overall
PDP-II System, and the basic instruction
set from a programming point of view. Includes some installation and interface
information.

Logic Handbook

DEC, 1971

Presents functions and specifications of the
M-series logic modules, accessories, and connectors used in the controller. Includes
other types of logic produced by DEC but
not used with PDP-ll devices.

Paper-Tape Software
Programming Handbook

DEC-I1-GGPB-D

Provides a detailed discussion of the PDP-II
software system used to load, dump, edit,
assemble, and debug PDP-ll programs; input/output programming; and the floating
point and math package.

A dot matrix impact printer and keyboard for use as a fullscale hard copy I/O terminal teletypewriter.
Keyboard is either 96 or 128 characters. Print set is 64 ASCII
characters, 80 characters per line, 10 characters per inch.

LCll Controller

Title

An interface between the DECwriter and the PDP-U Unibus.
Controls data transfers between the DECwriter and other
devices in a PDP-ll System. Also monitors printer status, indicates when the keyboard buffer is full, and enables the interrupt logic.
Also referred to as "control unit", "interface", and
" DECwriter control" .

1.2 SCOPE

This manual provides the user with the information necessary to operate the LCn
DECwriter System and provides the theory of operation and logic diagrams necessary
to understand and maintain the LCU Controller.
This manual and the appropriate LA30 DECwriter manual must be used together for a
complete understanding of the entire Lcn System. The prime subject of this manual ~s
the LCll Controller. In addition to providing complete coverage of the controller, thIS
manual includes sections covering overall system operation and programming.
The prime subject of the LA30 DECwriter Manual (DEC-00-LA30-DA) is the teletypewriter itself. The manual presents a detailed discussion of the print mechanism
and electronics including installation, operation, principles of operation, maintenance,
troubleshooting, and engineering drawings.

(

*Applicable PDP-II/IS manuals provide system coverage on PDP-II/IS Systems.

Table 1-1 lists related PDP-ll System documents that are applicable to the LCU
DECwrit~r System.
1-1

1.3 SPECIFICATIONS

Operating and physical specifications for the LCll Controller are given in Table 1-2.
Specifications for the LA30 DECwriter are given in Table 1-3.
Table 1-2
LeI1 Controller Specifications
Registers:

Keyboard Status Register (KBS)
Keyboard Buffer Register (KBB)
Printer Status Register (PRS)
Printer Buffer Register (PRB)

KBS
KBB
PRS

PRB

777560
777562
777564
777566

7-bit parallel character lin ASCII code

Interrupts:

Priority

= BR4

Vectors

= location 60 for keyboard (when used as

(keyboard slightly higher level
than printer because electrically
closer to processor)

location 64 for printer

1-2

Printing Speed:

30 characters/second, asynchronous
300 ms carriage return
30 line feeds/second

Print Characters:

64 upper case Ascn sub set
(lower case codes print in upper case)

Print Format:

5x7 dot matrix typeface
80 characters/line
10 characters/inch
6 lines/inch

Paper:

9 and 7/8 inch wide
tractor driven continuous form original plus one carbon
(can be adjusted for up to 6 copies)

Ribbon:

nylon, Yz inch by 120 feet

Keyboard:

96 characters (normal)
128 characters (optional)
USASCn 1968 characters

Dimensions:

20% inches wide
31 inches high
24 inches deep

Weight:

110 pounds

DC Power:

self-contained

Power Input:

300 watts, maximum
voltage and frequency dependent on model:
LA30 PA
115V/60Hz
230V/ 60Hz
LA30 PB
LA30 PC
115V/50Hz
LA30 PD
230V/50Hz

Temperature:

50°F to 130°F

Humidity:

5% to 90% (non-condensing)

(when used as console)

Data type:

Types

Table 1-3
LA30 DECwriter Specifications

console)

DONE (keyboard has loaded buffer)
READY (printer ready to receive data)

Bus Cycles:

DATI or DATOB

Status Indications:

DONE, READY, and ID (interrupt enable)

Size:

The LCll Controller occupies ~ of a DD Il-A or one
of two controller slots in a KAll or KCIl Processor
System Unit.

Power:

0.25A @+5V (derived from H720 Power Supply in
mounting box where controller is installed)

Cable:

25 feet
17 twisted pairs (TTL compatible parallel)
plus one spare pair

1.4 MAINTENANCE

The basic maintenance philosophy of the LCU DECwriter System is to present the user
with the information necessary to understand normal operation of the system. The user
can use this information when analyzing trouble symptoms to determine necessary
corrective action. It is beyond the scope of this manual to present detailed troubleshooting informa tion.
General PDP-ll maintenance information is presented in the PDP-ll Conventions
Manual, DEC-ll-HR6B-D as well as in the KAll Processor Manual, DEC-ll-HR2B-D
and the KCll Processor Manual, DEC-ll-HKCA-D. Detailed maintenance and troubleshooting information for the DECwriter itself is included in the LA30 DECwriter
Manual DEC-OO-LA30-DA.

1.5 ENGINEERING DRAWINGS

A complete set of reduced engineering drawings and module circuit schematics is
provided in a companion volume to this manual which is entitled, LCll DECwriter
System, Engineering Drawings. The general logic symbols used on these drawings are
described in the DEC Logic Handbook, 1971. Specific symbols and conventions are also
included in the PDP-ll Conventions Manual, DEC-ll-HR6B-D.

1.6 TERMINOLOGY

The PDP-ll Conventions Manual, DEC-ll-HR6B-D, contains a list of terminology and
abbreviations used with the PDP-ll family of systems. A glossary of PDP-ll terms, as
well as general computer and programming terms, is also included.

(
1-3

CHAPTER 2
GENERAL DESCRIPTION

2.1 INTRODUCTION

The LA30 DECwriter serves as an input (keyboard) and output (page-printer) device
for PDP-U Systems. The LCn Controller is an interface that handles parallel data
transfers between the DECwriter and the PDP-ll Unibus. The controller consists of
three integrated circuit modules mounted on one-fourth of a system unit <slots 13 or 14
in the DDU-A Peripheral Mounting Pane}). Thus, four DECwriter control interfaces can be
mounted in the space of a single system unit.
2.2 DECWRITER

The LA30 DECwriter is a dot matrix impact printer and keyboard designed for use as
a full-scale hard copy I/O terminal teletypewriter. The DECwriter operates at a speed
of up to 30 characters per second and prints on a continuous form paper. There are
four models available (refer to Table 2-1). The prime difference among models is the
input power requirement.

Signals transferred between the DECwriter and the LCU Controller consist of 7-bit
character codes and three control signals. All information, regardless of direction of
transfer, is transmitted in parallel. No start or stop codes are required. The 7-bit standard ASCII code is used for all printing and non-printing characters. Standard codes
for these characters are given in Appendix A.
The DECwriter is a free-standing, pedestal-mounted unit. All operating controls and indicators, with the exception of the power circuit breakers, are mounted on the front of
the DECwriter.
2.3 LCn CONTROLLER

Table 2-1
DECwriter Models

(

The DECwriter printing head is capable of printing 64 different characters under control of the interface. The printing head is advanced by a stepping motor that is controlled by solid-state logic. Seven spring-loaded wires in the print head are activated
by solenoids to impact a standard nylon ribbon in order to form the required character. No special thermal or electrostatic paper is needed and standard 80-column, fanfold paper is used. The DECwriter is normally set for single or two-sheet copy but up
to six-part paper can be used by readjusting the impact loading.

Model No.

Voltage

Frequency

LA30-PA

115 Vac

60Hz

LA 3O-PB

230 Vac

60 Hz

LA30-PC

115 Vac

50 Hz

LA30-PD

230 Vac

50 Hz

The DECwriter keyboard is capable of producing either a 128- or 97-character ASCII
subset. The letter keys are in a standard typewriter layout, and the additional printing
and non-printing (control) keys are laid out similar to a Teletype keyboard. The
keyboard inputs character codes into the interface but does not type directly on the
paper unless an echo program is used.

The LCn Controller handles data one character at a time by means of a program interrupt for parallel transfer to or from the Unibus. When the processor addresses the
bus, the LCn Controller decodes the incoming address to determine if the DECwriter is
the selected external device and, if selected, whether it is to perform an input or
output operation. For the following discussion, refer to the simplified block diagram
shown in Figure 2-1.
The address selector module decodes the incoming address and responds to one of four
possible sequential addresses. The register that is selected and the type of bus data
transfer operation being performed determine whether a keyboard or printer operation
is to be used. If , for example, the DECwriter has been selected to accept information
for printout, the controller waits for a READY flag, which indicates the printer is
available and is requesting a character from the controller. At this point, the controller
strobes a character from the bus into the printer buffer register for transfer to the
printer. The READY flag drops during the storage and print operation. The printer
READY flag is also used to activate the interrupt control module, provided the module
is enabled (lD true). The purpose of this module is to cause a program interrupt by
means of a specific vector address.
2-1

)
~

0<07:00>

BBSY SSYN
SACK BR-BG
INTR

U ~

BUS
DRIVERS

A<17:00>
C<1:0>
MSYN SSYN

I
1D

M782
INTERRUPT
CONTROL

I
B
U
S

PARALLEL DATA

I+-

I<EYBOARD
STATUS
REGISTER

DONE

KEYBOARD
BUFFER
REGISTER

M105
ADDRESS
SELECTOR

..,

BUS
RECEIVERS

READY

D
E

L C
A
3

I o

PRINTER
STATUS
REGISTER

I
I
I

0<06'00>

PARALLEL
DATA

PRINTER
BUFFER
REGISTER

•

W
R
I
T
E

PARALLEL
DATA
..AD

L __
11-0670

Figure 2-1

Len Controller-8implified Block Diagram

When recelvmg data from the DECwriter, the operation is essentially the reverse.
When the keyboard has assembled a character, it generates a KEY STROBE signal to
activate the interface and the 7-bit character is parallel loaded into the keyboard
buffer register. When the buffer is loaded, the interface sets a DONE flag, indicating
to the program that a character is ready for transfer to the Unibus. The DONE flag
activates the interrupt control module (if enabled), thereby causing a vectored interrupt.

2-2

The keyboard and printer status registers can be addressed and read by the program
to determine the status of the READY flag, DONE flag, and the two interrupt enable
(ID) bits.
Although the information transferred between the DECwriter and LCU Controller is a
7-bit ASCII character, the controller can add an eighth bit to the keyboard character
prior to loading the character onto the bus. This additional bit is controlled by jumpers
on the LCU.

CHAPTER 3
OPERATION

3.1 INTRODUCTION

This chapter provides the information necessary for normal operation of the LCU
DECwriter System and is divided into three major parts: controls and indicators,
keyboard, and paper installation. Additional operating procedures, such as ribbon replacement, calibration, and mechanical adjustments, are covered in the LA30
DECwriter Manual, DEC-OO-LA30-DA.
.

3.2 CONTROLS AND INDICATORS

a. front panel
r

"'\

The controls and indicators used to operate the LCU DECwriter System (with the exception of the keyboard) are shown in Figure 3-1 and listed in Table 3-1. The table lists
each control, its loca tion, type, and function.

3.3 KEYBOARD
CB2

The following discussion covers only certain operational notes regarding the keyboard.
It is beyond the scope of this manual to provide a detailed description of the keyboard.
A complete description is given in the LA30 DECwriter Manual, DEC-OO-LA30-DA.
The keyboard doestnot type directly into the printer; it simply sends the appropriate
ASCII code to the LCU Controller for transmission to the bus. Therefore, in order to
have the keyboard type directly on the paper, it is necessary to use an echo keyboard
program. An example of this program is given in Paragraph 4.6. Basically, the controller receives the code from the keyboard and then transmits the same code to the
DECwriter printer for printing. A pin on the back plane of the LA30 can set the printer
to a maintenance mode that connects the keyboard directly to the printer.

/'~

CB3

,....

r--CB1

[@]
'----

The keyboard can be set to produce either 97 or 128 characters even though the printer
is capable of printing only 64 different characters. The additional keyboard characters,
however, can be handled by the LCU Controller for transfer to another'device, such as
a 96-character line printer. Because many of the additional keyboard characters are
actually control commands, an output printing device may have fewer characters than
the associated keyboard.

b. rear panel
11-0671

Figure 3-1

DECwriter Controls and Indicators
3-1

Step

Procedure

Raise cam lever located on left-hand side of print bar assembly
until it disengages. Slide the bar assembly back.

Feed paper from its box on the floor under the DECwriter up
through the opening in the bottom of the base plate casting.
Pull fresh supply into the machine; discard any unused portions of the previous supply.

Make certain paper is feeding straight and then engage paper
with the sprocket feed wheels.

When printer is being used, light goes out during print operation to indicate printer cannot
receive additional data and keyboard cannot
be used until print cycle is complete. Light
comes on when printing is completed.

Advance paper by rolling knobs. Make certain paper rolls
smoothly.

Feed end of paper over lid and close lid, making certain that
both ball studs latch to the base assembly.

Place circuit breaker CBl to the on (up) position.

Table 3-1
Controls and Indicators
Control or
Indicator

location

READY
indicator

front
panel

Function

Type
single bgh t
(white)

)

\Vhen lit, indicates that power has been applied
to the system and the DECwriter is ready for
use in either an input (keyboard) or output
(printer) mode.
If keyboard is being used, indicates an interrupt
has been initiated provided ID bit has been set
in the controller.

LOCLF
switch

front
panel

pushbutton
switch with
indicator

When depressed, advances paper one line. Keyboard and printer operation disabled during
line feed. This is an off-line operation and has
no effect on the controller.

CB3

rear
panel

circuit breaker
2-position
toggle switch

When set to on (up) position, applies power to
printer head electronics.

CB2

rear
panel

circuit breaker
2-position
toggle switch

When set to on (up) position, applies power to
printer stepping motor electronics.

CBl

rear
panel

circuit breaker
double-pole,
single throw

When set to on (up) position, applies primary
power to the DECwriter.

PULL UP
CAM LEVER
)'J'"
TO RELEASE f

PUSH PRINT

<--- BAR ASSEMBLY
BACK

PRINT HEAD
ASSEMBLY

®_ _-+-+- RETAINING

SUPPORT
BAR
BACKSTOP
WAYS

STUD

3.4 LOADING PAPER

The proper procedure for loading paper into the LA30 DECwriter is detailed below and
shown in Figure 3-2.
Step

Procedure

Set main power circuit breaker CBl to the off (down) position.

Open DECwriter cover by pressing up on both sides of front
panel.
CAUTION

Release both baH studs from their spring
retainers at approximately the same time to
avoid skewing and/or damage to the top
cover.
3-2

PAPER
SUPPLY
11-0672

Figure 3-2

Loading Paper into LA30 DECwriter

CHAPTER 4
PROGRAMMING INFORMATION

Table 4-1
Standard Device Register Assignments

4.1 SCOPE

This chapter presents general programming information for software control of the
LCl1 DECwriter Controller. Although a few typical program examples are included, it
is beyond the scope of this manual to provide detailed programs. For more detailed information on programming, refer to the Paper-Tape Software Programming Handbook,
DEC-ll-GGPB-D.
This chapter is divided into four major portions:
a. device registers
b. interrupts
c. timing considerations
d. programming examples

Mnemonic

Address

Keyboard Status Register

KBS

777560

Keyboard Buffer Register

KBB

Printer Status Register

PRS

777562
777564

Printer Buffer Reigster

PRB

777566

UNUSED

UNUSED
11-0673

4.2 DEVICE REGISTERS

Figure 4-1 Keyboard Status Register - Bit Assignments

All software control of the LCU DECwriter Controller is performed through four device
registers. These registers have been assigned memory addresses, and can be read or
loaded using any PDP-l1 instruction that refers to their address.
The four device registers and associated addresses are listed in Table 4-1. Note that
these addresses can be changed by altering the jumpers on the M105 Address Selector
Module. However, any DEC programs or other software referring to these addresses
must also be modified accordingly if the jumpers are changed.
Figures 4-1 through 4-4 show the bit assignments within the four device registers. The
" unused" and "load only" bits are always read as zeros. Loading "unused" or
"read only" bits has no effect on the bit position. The mnemonic INIT refers to the
initialization signal issued by the processor. Initialization is caused by one of the following: issuing a programmed RESET instruction; depressing the START switch on
the processor console; or occurrence of a power-up or power-down condition of the
processor power' supply.

Bit

Designa tion

15-08

Unused

Not Applicable

DONE

Indicates that a character is available in
keyboard buffer register. Cleared by INIT
or by referencing keyboard buffer. Causes
interrupt when ID (bit 06) equals 1. Read
only.

Interrupt enable on DONE. When this bit is
set, enables DONE (bit 07) to cause an interrupt. Cleared by INIT.

05-00

Unused

Meaning and Operation

Not Applicable

(
4-1

Bit

UNUSED

Designa tion

]

DATA

Meaning and Operation

Bit

Designa tion

Meaning and Operation

Note that the printer sets READY
approximately 2 us after it receives a
carriage return (CR) command. This
permits non-:-printing characters, such as
line feed, to be received during carriage
return time. If a printing character is received during carriage return time,
READY is cleared and is then set after CR
and printing are complete.

15-07

Unused

Note that bit 07 is not offered as parity
option with the LA30.

When set READY causes an interrupt
provided ID (bit 06) is set. Read only bit.

06-00

Data Buffer

7-bit ASCII character buffer. Holds character read in from the LA30 keyboard. Read
only. Cannot be loaded from the bus.

11-0674

Figure 4-2 Keyboard Data Buffer Register-Bit Assignments

NOTE
Any reference to KBE (as
word or byte) or to
KBB+l, clears DONE in
the keyboard status register.

05-00

Unused

Interrupt enable bit. When this bit is set, it
enables READY (bit 07) to cause an interrupt. Cleared by INIT.
Not Applicable

UNUSED

DATA
11-0676

Figure 4-4 Printer Data Buffer Register-Bit Assignments
UNUSED

UNUSED

11-0675

Figure 4-3 Printer Status Register-Bit Assignments
Designa Hon

Meaning and Operation

15-07

Unused

Note that bit 07 is not offered as a parity
option with the LA30.

Meaning and Operation

Bit

Designa tion

15-08

Unused

Not Applicable

READY

This bit is set whenever the printer is
ready for the next charader to be loaded.
Indicates that the previous function is
either complete or has been started and
continued to a point where the printer can
accept the next command. This bit is set
only by the LCll Controller.
This bit is set when power is applied to the
LA30 and cleared by the leading edge of
the PRINT STROBE signal, which indicates that the printer has received a
command.

4-2

Bit

06-00

7-bit ASCII character buffer. Transfers
data from the Unibus to the LA30 printer.
Holds the data strobed in from the bus
until the READY bit is set, which indicates
that the printer is ready to receive the
data.
NOTE
Any instruction (word or
byte) th~t modifies the
printer da ta buffer clears
the READY bit and initiates the print cycle.

Load only.

4.3 INTERRUPTS

a. Reading a Character (from Keyboard)

The LCn Controller uses BR interrupts to gain control of the bus in order to perform
data transfers. When the processor grants the requestand other Unibus conditions are met,
the Len gains conrtrol of the bus (becomes bus master) and performs a DATI or DATO to
transfer data directly to or from the Unibus.
When the keyboard DONE flag is set, it activates the interrupt control so that it can
notify the processor that a character has been assembled. When the printer READY
flag is set, it activates the interrupt control so that it can notify the processor that another character can be loaded into the printer buffer.
The keyboard initiates an interrupt whenever DONE = I and ID = I both become true.
The vector address is 60. The printer initiates an interrupt whenever READY = I and
ID =1 both become true. The vector address in this case is 64. The standard priority interrupt level is set at the BR4 level for both the keyboard and the reader. The
keyboard has a slightly higher priority because it is electrically closer to the processor
on the BG4 level.
Although the vector addresses and priority level are standard, they can be changed by
the user, if desired. However, all DEC programs reference the standard addresses and
priority and, therefore, must also be changed if the standard assignments are changed.
4.4 TIMING CONSIDERATIONS

(

The LCll Controller provides parallel operation on the bus and operates in a
demand response mode; therefore, there are no special timing requirements that must
be considered.

LOOP:

TST8 TKS

READ:

BPL LOOP
MOV TKB"R0

;LOOK FOR DONE
;WAIT IF DONE=0
;READ CHARACTER

b. Echoing Keyboard

ECHO:

T5T8 TKS

BPL ECHO
WA IT:

TST8 TPS

BPL WAIT
MOV TKB"TPB
BR ECHO

;CHARACTER AVAILABLE?
;WAIT IF DONE=0
.;IS PRINTER READY?
.;WAIT IF READY=0
;PRINT CHARACTER
;REPEAT FOR NEXT CHARACTER

The basic operating times of the keyboard and printer are as follows:
Keyboard

Maximum key-in rate = 30 cps
time between buffer loads = 33.3 ms

Printer

Printing rate = 30 cps
carriage return time = 300 ms
line feed time = 33.3 ms
time between buffer loads = 33.3 ms

4.5 PROGRAMMING NOTE
If any difficulty is experienced when reading the keyboard buffer register (KBB), in-

spect the jumpers at WI and W2 on the M79I Module. There must be a jumper at
either WI or W2 but not both or processor errors occur when attempting to read the
buffer. The use of these jumpers is described more fully in Paragraph 5.4.
4.6 PROGRAMMING EXAMPLES

The following examples represent typical programs for reading a character from the
keyboard and for echoing the keyboard.

(
4-3

CHAPTER 5
THEORY OF OPERATION

5.1 INTRODUCTION

This chapter provides a detailed description of the LCU DECwriter Controller. The
controller may be divided into four major functional areas: selection logic, interrupt
logic, keyboard logic, and printer logic. Each of these areas is covered separately in
subsequent paragraphs. The purpose of each of these functional areas is as follows:
Selection Logic

Determines if the DECwriter has been selected for use, which
register is to be used, and wha t type of transfer (DATI or
DATOB) is to be performed. Consists of the M105 Address
Selector Module.

Interrupt Logic

Permits the controller to gain bus control and perform a
program interrupt. Priority level of bus request (BR) line may
be changed by user. Consists of the M782 Interrupt Control
Module and the ID (interrupt enable) bits in the keyboard and
printer status registers (M791 Module>.

Keyboard Logic

Printer Logic

Consists of a data buffer that receives one character from the
keyboard for parallel transmission to the bus and a status register that indicates to the program when the character has been
loaded. Also provides the interrupt enable bit so that the character can be transferred by means of an interrupt. Part of
M791 Module.
Consists of a data buffer and a status register. The buffer holds
data strobed in from the bus until the printer is ready for use,
at which time it transfers the data to the printer. The status
register indicates when the printer is ready and also provides
an interrupt enable bit so that the data can be transferred by
means of an interrupt. Part of the M791 Module.

5.2 SELECTION LOGIC

(

The MI05 Address Selector Module decodes the address information from the bus and
provides four select line and two gating signals that determine which register has been
selected and whether it is to perform an input or output function. The MI05 Module
jumpers are arranged so that the module responds only to standard device register addresses 777560, 777562, 777564, and 777566 (jumpers in bit positions 3 and 7). Although

these addresses have been selected by DEC as the standard assignments for the LCU
DECwriter Controller, the user may change the jumpers to any address desired. However, any MainDEC program (or other software) that references the LCU standard
address assignments must be modified if other than the standard assignments are
used.
The first five digits of the address (77756) indicate that the LCU has been selected as
the device to be used. The final digit, consisting of address lines A02, A01, and AOO,
determines which register has been selected and whether a word or byte operation is
to be performed. Actually, the operation is always a byte operation even if a word operation is selected because bits 8 through 15 in all four registers are unused. The two
mode control lines, COO and COl, determine whether the selected register is to perform
an input or output operation.
Address lines A02 and AOl are decoded by the MI05 to produce one of four select line
signals, which select the register to be used (refer to Table 5-1). The two mode control
lines produce IN and OUT gating signals (Table 5-1) that determine whether the bus
cycle is a DATI or DATO. Note that an IN gating signal is not supplied for select line
6 (printer buffer register) because the printer buffer cannot be read from the bus; it is
a load only register. Note also, that an OUT gating signal is not provided for select
line 2 because the keyboard buffer is a read only buffer and cannot be loaded from the
bus.
It is beyond the scope of this manual to cover operation of the MI05 Address Selector

Module; detailed descriptions of this module are covered in the 1971 DEC Logic Handbook and in the Unibus Interface Manual, Second Edition, DEC-U-HIAB-D.

5.3 INTERRUPT CONTROL

The M782 Interrupt Control Module (drawing D-CS-M782-0-1) permits the LCU Controller to gain control of the bus (become bus master) and perform an interrupt operation. The M782 Module jumpers are arranged so that the module has normal vector
addresses of 60 and 64 (jumpers in bit positions 3, 6, and 7). Although these are the
recommended vector addresses, the user can change the jumpers to correspond to any
address desired, but MainDEC programs reference the standard vector address assignments of 60 and 64. Note that changing the jumpers affects only the first part of the
vector addresses. The last digit is controlled internally by the M782 Module and is
always either 0 or 4.
5-1

Table 5·1
Ga ting and Select Line Signals
Select
Line

Gating
Signal

Function
Selected

Reg.

Keyboard status to bus

KBS

DATI

Keyboard buffer to bus

KBB

DATI

Printer status to bus

PRS

DATI

OUT

Bus to keyboard status

KBS

DATO or DATOB

OUT

Bus to printer status

PRS

DATO or DATOB

OUT

Bus to printer buffer

PRB

DATO or DATOB

Bus
Cycle

The M782 Module contains two completely independent request and grant acknowledge
circuits (channels A and B) for establishing bus control. Channel A is used with the
keyboard logic; channel B is used with the printer logic. The module has a priority
level of BR4, with the A channel (keyboard) slightly higher in priority because it is
electrically closer to the processor. Note that the priority level can be changed by
means of the priority plug. However, any programs referring to the BR4 level must
also be changed. All DEC software references the standard priority level.
Before the M782 Module can generate an interrupt request, two input signals must be
high: INT ENB and INTERRUPT. Because both of these signals are needed for each
channel, there are actually four signals developed by the logic: INT ENB A and TNT A
for channel A, and INT ENB Band INT B for channel B. Generation of these signals
is discussed below. It is beyond the scope of this manual, however, to cover operation
of the M782 Module itself. Detailed descriptions of the M782 Interrupt Control Module
are covered in the 1971 DEC Logic Handbook and in the Unibus Interface Manual,
Second Edition, DEC-ll-HIAB-D.
When the keyboard done (DONE) flag is set, it activates the interrupt control A channel so that it can notify the processor that a character has been loaded into the controller and is ready for transfer to the bus. Thus, the keyboard initiates an interrupt
whenever DONE = 1 and ID = 1 both become true.
The logic for the keyboard interrupt signals is shown on drawing D-CS-M791-0-1. When
the ID (interrupt enable) bit is loaded by the program, a 1 is loaded onto bus data line
D06, which is the D input to the INT ENB A flip-flop. The C input to the flip-flop is
high when both SELECT 0 and OUT LOW are high, indicating that the keyboard status
register has been selected for loading.
These two inputs set the flip-flop which produces the INT ENB A H pulse that is the
enabling signal for the A channel in the M782 Module. When the DECwriter produces a
KEY STROBE signal, indicating a character is ready for transfer (DONE), it sets the
INT A flip-flop which produces the INT A H pulse that causes the A channel of the
M782 to initiate an interrupt.

input to this flip-flop is high when both SELECT 4 and OUT LOW are high, indicating
that the printer status register has been selected for loading. These two inputs set the
flip-flop which produces the INT ENB B H pulse that is the enabling signal for the B
channel in the M782 module. When the DECwriter is ready to receive data, it issues a
P DEMAND H signal (READY). This signal becomes the INT B H pulse that causes
the B channel of the M782 to initiate an interrupt.
Note that the same bus data line (D06) is used as an input for both the INT ENB A
and B flip-flops. Therefore, any time a 1 is loaded into bit position 06, the D lines of
both flip-flops are true. However, the flip-flop that becomes set is dependent on the C
line input which consists of the SELECT line and GATING signals used to reference
either the keyboard or printer sta tus register.

5.4 KEYBOAR.D LOGIC

During keyboard operation of the DECwriter, the keyboard buffer register in the controller receives each character as it is produced. The character is stored in the buffer
until placed on the Unibus for transfer to memory or some other bus device. The
keyboard buffer and associated logic is shown on drawing D-CS-M791-0-1.
Whenever a key on the DECwriter keyboard is depressed, the DECwriter logic produces a 7-bit ASCII code that represents the symbol shown on the key. This 7-bit code is
applied in parallel to the data input lines of the seven flip-flops comprising the
keyboard buffer register. After the data has had time to settle, the DECwriter issues a
KEY STROBE signal, which is inverted and used as a clock input for the seven flipflops. Thus, when the KEY STROBE is issued by the DE Cwriter , it strobes the information on the data lines into the buffer. At this point, the status of each flip-flop (set
or cleared) corresponds to the information that was placed on the corresponding data
line by the DECwriter.
The output of each flip-flop is tied to one input of an associated 2-input AND gate. The
other input for all seven gates is connected to an AND gate that is true only when both
SELECT 2 and IN are true, which indicates the buffer has been selected for reading.
When these conditions are true, the buffer output is coupled to bus data lines DOO
through D07.
As explained in Paragraph 5.3, the KEY STROBE signal also sets a flip-flop that produces the INT A H signal that initiates an interrupt request so that the contents of the
buffer can be transferred to the bus. This INT A H signal is also applied to one leg of
a 2-input AND gate to provide the DONE indication (bit 07) in the keyboard status register. The other input to the AND gate is qualified when the keyboard status register is
addressed for reading (SELECT 0 H and IN H are both true).
An eighth data bit can also be gated onto the bus (line D07) if desired. However, this
bit does not come directly from the DECwriter keyboard but is provided by a jumper
on the controller module. If a 1 is desired in this bit position, then a jumper is added
at WI; if a 0 is desired, a jumper is added at W2.

CAUTION'

The logic circuits for the printer interrupt signals is also shown on drawing D-CS-M7910-1. When the ID (interrupt enable) bit in the printer status register is set, a 1 is
loaded onto bus data line D06, which is the D input to the INT ENB B flip-flop. The C
5-2

A jumper must always be connected to either WI or W2, but not both.
If both WI or W2 are jumpered, or if neither WI 411' W2 are jumpered,
a processor err41r 41ccurs.

(

Note that there is no bit 00 for the keyboard. The keyboard data bits are numbered 1
through 7 (KBl through KB7 on the drawing) and correspond to bus data lines DOO
through D06 respectively. Thus, for example, keyboard bit 3 is read on bus data line
D02.
5.5 PRINTER LOGIC

During printer operation of the DECwriter, a character from memory or some other
bus storage device is transferred to the DECwriter for printing. When a print operation
is desired, the LCn Controller must wait for a READY flag to be set, indicating that
the DECwriter is ready to receive a character for printing. This flag is set by the
printer logic and cannot be controlled by the Le11 Controller. When the READY flag is
received, it causes an interrupt to be generated, and the controller loads a character
from the bus into the printer buffer register (PRB). This character and a print command signal are strobed into the DECwriter. The DECwriter immediately drops the
READY flag to indicate that it is busy and cannot accept another print command at
this time, and then prints out the character. After the character is printed, the READY
flag is again set, and the process repeated for the next character from the bus. The
printer buffer register and associated logic is shown on drawing D-CS-M791-0-1.
Whenever the DECwriter is ready for printing (keyboard not in use), it sets the
READY flag, which is applied to the LCn Controller as the P DEMAND H signal. This
signal passes through a gate and inverter and is applied to the M782 Interrupt Control
Module as INT B H. Thus, an interrupt is generated by READY provided bit 06 (ID)
in the printer status register is set. Bit 06 causes the INT ENB B H signal to be generated. Interrupts are described in Paragraph 5.3.

5.6 INTERFACE SIGNALS

All signals to or from the DECwriter are true in the high state (+3V). The operational
state of the DECwriter is determined by two signals (KEY STROBE and P DEMAND
H), which are applied from the DECwriter to the LCn Controller logic. The KEY
STROBE signal indicates that the DECwriter keyboard is in use, the P DEMAND H
indicates that the printer is able to accept a character for printing. Either one, but not
both, of these signals may be true at any given time.
Eight input lines originate in the controller logic and terminate in the DECwriter.
Seven of these are PRINTER DATA lines (POl through P07) and the eighth is the
STROBE line. When the STROBE line goes true, data on the seven PRINTER DATA
lines is parallel transferred into the printer, causing P DEMAND H to go low until the
printer logic has shifted the printable character into its associated memory.
Eight output lines originate in the DECwriter and terminate in the controller logic.
Seven of these are KEYBOARD DATA lines (KB1 through KB7) and the eighth is the
KEY STROBE line. When the KEY STROBE line goes true, data on the seven
KEYBOARD DATA lines is parallel transferred into a controller flip-flop register. This
registb stores the character until it is loaded onto the Unibus for transfer to some
other bus device such as memory.
All interface signals are shown in Figure 5-1 and listed in Table 5-2 along with their
related function. The signal names used on the table are the functional names; the
name in parenthesis indicates the nomenclature used on the print set. Table 5-3 lists
these same interface signals, but includes wiring information. A complete list of ASCII
codes (as used in the LA30 DECwriter) is given in Appendix A.

The P DEMAND H signal is also applied to one leg of a 2-input AND gate connected to
bus data line D07. The other leg of the gate is qualified whenever the printer status
register (PRS) is selected for reading (SELECT 4 H and IN H both true). Therefore,
the P DEMAND H signal sets the READY bit (bit 07) in the printer status register.

BIT 01

BIT02 H
BIT03 H
BIT04 H
BIT05 H

When the interrupt request is granted, the controller loads a character into the
DECwriter, issues a print command, and clears the READY bit in the status register.
This sequence is described in the following paragraphs.
During the interrupt, the program addresses the printer buffer register and places a 7bit ASCII code, representing one character, on Unibus data lines DOO through D06. The
levels on the bus lines are inverted and applied to printer input lines POI through P07
respectively. Note that there is no printer POO line. Therefore, bus line DOO feeds printer line POI, bus line DOl feeds P02, etc.
As soon as the program addresses the printer buffer register, the SELECT 6 Hand
OUT LOW H signals become true and qualify a gate to produce STROBE L. The
STROBE L signal is the print command sent to the DECwriter (referred to as PRINT
STROBE in the printer logic). When the printer receives the print command, it starts
printing the data from the buffer and drops the READY flag, causing P DEMAND H
to go low. If the program addresses the printer status register while P DEMAND H is
still low , the READY bit is clear because P DEMAND H being low inhibits the gate
for bit 07.

BITOG H
BIT07 H

I
N
T
E
R
F

A
C
E

INIT

L
A

PRINTER READY

:3
0

KEYBOARD STROBE

BITOl L
BIT02 L
BIT03 L
BIT04 L
BIT05 L
BITOS L
BIT07 L
11·0678

(

Thus, when the printer buffer register is addressed, a print command is issued, data is
gated from the bus into the DECwriter, and the READY flag drops.

Figure 5-1 Interface Signals
5-3

Table 5-3
Controller Input/Output Signals

Table 5-2
Controlier-DECwriter Interface Signals
Signal
READY
(P DEMAND H)

Source

Function

Signal Name

Direction

Lell Pin

DECwriter

Indicates to the user's system that the DECwriter
printer is available for use; synchronizes data transmission between the DECwriter and LCII Controller.

KEYBOARD
DATA

From LA30

The P DEMAND H signal requests a character from
the controller and this signal remains true until the
PRINT STROBE signal is received. The READY indication (P DEMAND H) is disabled while the character is being stored in memory and during the print
operation. When printing is complete, READY
again becomes true unless KEY STROBE is true.

KEYBOARD
DATA
Bit 01
Bit 02
Bit 03
Bit 04
Bit 05
Bit 06
Bit 07

From LA30

PRINT STROBE
(STROBE)

Controller

PRINTER DATA
(POI - P07)

Controller

KEY STROBE

KEYBOARD DATA
(KBI - K(7)

DEC writer

DECwriter

STROBE indicates that the printer can accept the
infonnation on the PRINTER DATA lines. Each
time the STROBE signal occurs, the DEC writer
printer samples the data lines and READY goes
false while the data character is being stored.
PRINTER DATA is coded information transmitted
from the controller to the printer on seven data lines.
Each character of the ASCII character set is transmitted as a 7-bit PRINTER DATA signal.
KEY STROBE indicates when the keyboard has
generated a character for transfer to the controller.
Each time the KEY STROBE signal occurs, the controller initiates an interrupt, samples the KEYBOARD
DA T A lines, and stores the character in a buffer for
transfer to the bus.
KEYBOARD DATA is coded information transmitted in parallel from the DECwriter keyboard to
the controller on seven data lines. Each character of
the ASCII character set is transmitted as a 7-bit
KEYBOARD DATA signal.

LA30 Pin

Signal Functi?n

Indicates character is ready in keyboard
buffer

N
L

These seven data bits represent the
ASCII code for the character being transmitted from the keyboard.

J
T

S1
D2
H2
M2
P2
S2
T2

PRINTER
From LA30
READY
(PDEMANDH)

Indicates printer is ready to accept a
character from the interface.

PRINT
STROBE
(STROBE)

To LA30

Print command that causes printer to accept data and print it out.

PRINTER
DATA
Bit 01
Bit 02
Bit 03
Bit 04
Bit 05
Bit 06
Bit 07

To LA30

INIT L

To LA30

V
R

11
LL

Dl
£1
HI

TT
RR
DD

K2
Ll
PI

These seven data bits represent a character from the controller that is being transferred to the DECwriter for printing.

Ini tializes prin ter .

The controller may add an eighth bit to this data
prior to loading on the bus.
'l'

5-4

APPENDIX A
CHARACTER CODES

~
BI

~ b 4 b 3 b 2 b,

0
0

0
1

NUL

0
2

0
4

SOH

DC1

STX

DC2

ETX DC3

EOT

DC4

ENQ

NAK

0/0

ACK

SYN

BEL

ETB

CAN

(

)

[

{

ROW ~

DLE

(0)

SUB

ESC

;

]

}

DEL

128 - CHARACTER SET (KEYBOARD)

96- CHARACTER SET (KEYBOARD)

64-CHARACTER SET (PRINTER)
11-0677

(

LCI1 DECwriter SYSTEM MANUAL
DEC-ll-HLCA-D

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