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DEC-OB-ASAC-D

PAL

III

PDP—8

SYMBOLIC

ASSEMBLER

PROGRAMMING

MANUAL

For additional copies order No. DEC—08-ASAC—D From Program

Digital Equipment Corporation, Maynard, Massachuseffs

DIGITAL

EQUIPMENT

CORPORATION

MAYNARD,

Library,

Price $1.00

MASSACHUSETTS

1st Printing August 1965
2nd Printing Rev June 1967
3rd Printing November 1967
4th Printing Rev May 1968
5th Printing Printing October 1968
6th Printing February 1969

Instruction times,

operating speeds and the like are in-

cluded in this manual forreference only; they are not to
be taken as specifications.

The following are registered trademarks of Digital

Equipment Corporation, Maynard, Massachusetts:
DEC

PDP

FLIP CHIP

FOCAL

DIGITAL

COMPUTER LAB

PREFACE

The PDP-8 comes to the user complete with an extensive selection of system programs and routines making

the full data processing capability of the new computer immediately available to each user,
many commonly experienced initial

eliminating

programming delays.

The programs described in these abstracts come from two sources, past programming effort on the PDP-5

computer, and present and continuing programming effort on the PDP—8.

Thus the PDP-8 programming

system takes advantage of the many man—years of program development and field testing by PDP—5 users.

Although in many cases PDP—8 programs originated as PDP—5 programs, all utility and Functional program
documentation is issued in a new, recursive Format introduced with the PDP—8.

Programs written by users of either the PDP—5 or the PDP-8 and submitted to the users' library (DECUS

—

Digital Equipment Corporation Users' Society) are immediately available to PDP—8 users.

Consequently, users of either computer can take immediate advantage of the continuing program developments for the other.

...

III

CONTENTS
Page

_C_h_a__pt_er
I

INTRODUCTION

ILLUSTRATIONS OF PDP-8 ASSEMBLER FEATURES

.....................................................

........................

2-]

.............................................

2—l

...............................................

2—I

The Location Counter

Coding Illustrations

THE SOURCE LANGUAGE

The Character Set

.............................................

3-1

................................................

3-I

..............................

.......................

3—l

...............................

.......................

3—I

Letters

Digits

Punctuation Characters

....................

3—l
3-2

Illegal Characters

............................................

3-2

................

3—2

.....................................................

3-2

............................

3-3

.............................................

3—3

................................................

3—4

......................................................

3-5

...............

Symbol

.....

......

Parameter Assignments

Symbol Definition
Expressions

Comments

......

Pseudo-Instructions

..............

.............

.........

3-8

................................................

3—9

...............................................

3-9

.....................

4—I

....................................................

4-I

PROGRAM PREPARATION AND ASSEMBLER OUTPUT

Program Tape

OPERATING INSTRUCTIONS

Summary

..........................................

Current Address Indicator

............................................

Number

...................

Ignored Characters

Elements

I—I

..........................................

........................................................

SYMBOL TABLE ALTERATION

.........................................

5-]
5-2

6—I

CONTENTS (continued)
Page

Appendix
I

SYMBOL LISTS

ASCII CHARACTER SET

...............................................

A1—]

.................................................

A2-1

........

CHAPTER

INTRODUCTION

The use of an assembly program has become standard practice in the programming of digital computers.
Use of an assembler permits a programmer to code in a more convenient

The advantages of this practice are widely recognized:

language than basic machine code.

Easily recognized mnemonic codes are used in—

stead of numeric codes; instructions or data may be referred to by a symbolic name; decimal data may be
used as such with the assembler making the required decimal-to-binary conversion; programs may be al—

tered without extensive changes in the source language; and debugging is simplified.

The basic process performed by the Assembler is the substitution of numeric values for symbols, according
to associations

found in the symbol table.

In addition, the user may request that the Assembler itself as-

sign values to the user's own symbols at assembly time.

These symbols are normally used to name memory

locations, which may then be referenced by name.
The ability to use mnemonic names to represent machine instructions is of great value.
minds the user of the Two's complement ADdition instruction, while the number

quently, the instructions are easier to remember when mnemonics are used.
names.

The name TAD re—

Iflflg does not.

Conse—

The same is true of location

It is much easier to associate the name TOTAL with the location containing the accumulated

total than it is to remember that location I374 contains the total.

Another advantage is that, since the assignment of absolute numbers to symbolic locations is done by the

Assembler, the updating of a program by adding or removing instructions is simplified.
In addition to translating statements directly into their binary equivalents, the Assembler will accept in—
structions for performing translations.

but they do not generate binary codes.

These instructions may not look different from other instructions,
For this reason,

they are referred to as pseudo—instructions.

For

example, the pseudo-instruction DEClMAL tells the Assembler that all numbers following in the program
are

be taken as decimal rather than as octal

has no binary equivalent in the obiect program

This instruction is important to the assembly process but

Certain other features of assembly can be directed to the

Assembler by the setting of the switch register, abbreviated SR.
The PDP-8 Assembly System consists ofthe Assembler (PAL III) and the Binary Loader (DEC-O8— LBAA-PM)
source

program prepared in the source

language using ASCII code is translated by the Assembler into a

binary object tape in two passes through the Assembler.
Loader into the computer ready for execution.
I—I

The object binary tape is loaded by the Binary

During the first pass of the assembly, all symbols are defined and placed in the Assembler‘s symbol table.
During the second pass, the binary equivalents of the input source language are generated and punched.
The Assembler has an optional third pass, which produces an "assembly listing,

or a

listing with the lo-

cation, generated binary, and source code side by side on a line.
The PDP—8 Assembly system also includes the Symbolic Tape Editor (DEC-OB-ESAB-D) For altering or

editing the source language tape; the DEC Debugging Tape (DDT-8, DECvOS-CDDA-D) for debugging
the object program by communicating with it in the source

language, and various other utility programs

such as dumps, etc.

The Assembler requires a basic PDP-8 system consisting of the ASR33 Tape Reader and Punch and a 4K
core

memory.

The Assembler can use either the High-Speed Reader, the High-Speed Punch, or both.

The basic Assembler allows 590 user symbols when using the ASR33 and allows 495 user symbols when

using the high speed reader. The Extended Assembler contains additional symbols For all optional
devices.

This symbol list is to be found in the Appendix.

CHAPTER

ILLUSTRATIONS

PDP-8

ASSEMBLER

FEATURES

THE LOCATION COUNTER
In general, statements generate l2-bit binary words which are placed into consecutive memory locations

when the object tape is loaded.

The location counter is a register used by the PDP-8 Assembler to keep

track of the next memory location available.
counter may

It is updated after processing each statement.

be explicitly set by an element or expression preceded by an asterisk.

The location

The element or ex-

pression following the asterisk sets the current location counter to the value of that element or expression.

Subsequent instructions are assembled into subsequent locations.
Example:
*

31555

The next instruction would be placed in location 3%.

The location counter is initially set to flZflfl.

CODING ILLUSTRATIONS
To illustrate some of the Features of the PDP—8 Assembler,
a

number of different ways.

is positive, then halts.

The routine continually adds I

small routine has been chosen and coded in
to

the contents of a location until the result

The instructions used are represented as their octal codes (more compact than the

binary actually used). The number being incremented is in location l7fl. The notation C(A) means the
contents of location A.

“W
*UJI
“”2
“”3
“‘54
“”5
“‘56

“7‘5

II7I2I

/C(I7;2I) INTO AC

7W1

/ADD I TO AC

317g

/STORE IN LOCATION 17¢

H791

/FETCH C0753)

77w!

/SKIP ON POSITIVE AC, CLEAR AC

51m

/JUMP TO LOCATION my:

74m

/HALT

/W|LL CONTAIN NUMBER TO BE INCREMENTED

Since the location counter is automatically incremented,

avoided after the first address in the progression.

have been used in place of the octal codes.

specifying sequential addresses could have been

In addition, the names of the PDP-8 instructions could

The octal representation of these instructions is substituted

by the Assembler whenever symbols appear in the program.
2—I

Example 2:

”W
TAD

17g

lAC
TAD

17¢
17g

SPA

CLA

JMP

1ng

DCA

HLT
*l7‘5

The same program could have been written using symbolic address tags.

The comma after the symbol A

indicates to the Assembler that the location in which it places the instruction TAD B is to be named A.

Information associating the symbol A with the number of actual locations is placed in the Assembler's sym—

Consequently, when processing the instruction JMP A, the Assembler finds the symbols JMP

bol table.

and A in the symbol table and uses these values to form the binary equivalent of the instruction JMP A.

Example 3:
”W
A,

TAD B

lAC
DCA B
TAD B
SPA CLA
JMP A
HLT

*l7,0'
B,

Unless the user specifically wanted to use location l7¢ for storage, he could let the Assembler assign the
location.

Example 4:

*IW
A,

TAD B

lAC
DCA B
TAD B
SPA CLA
JMP A

HLT

2-2

CHAPTER
THE

SOURCE

This chapter explains the featuresofthe ASCll source

LANGUAGE

language available to the user of PAL lll

THE CHARACTER SET
Letters

ABCDE...XYZ

Digits

123456789¢
Punctuation Characters

Since a number of characters are invisible (i .e.

nonprinting), the following notation is used to represent

them in the examples:
L—J

space

tab

—>|

)

carriage return

The following characters are used to specify operations to be performed upon symbols or numbers:
Character

r_;

space

combine symbols or numbers

plus

combine symbols or numbers

minus

combine symbols or numbers

carriage return

terminate line

—>l

tab

combine symbols or numbers or format the

source

tape

comma

assign symbolic address

equals

define parameters

asterisk

set current

semicolon

terminate coding line

dollar sign

terminate pass

3—]

location counter

point

has value equal to current location counter

slash

indicates start of a comment

lgnored Characters
form teed

end of a logical page of a source program (See Symbolic Editor DEC-08-ESAB-D)

blank tape

used for leader/trailer

rubouts

used for deleting characters

code 2%?

used for leader/trailer

line feed

follows carriage return

lllegal Characters
All other characters are illegal and cause the Illegal Character error printout:
PASSl
rent

lC dddd AT dddd during

The First number is the value of the offending character, and the second is the value of the cur-

location counter where it occurred.

lllegal characters are ignored.

ELEMENTS
.

Any group of letters, digits, and punctuation which represents binary values less than 2

element.

Number

Any sequence of numbers delimited by punctuation characters forms a number.

Example:
1
l2

4372

The radix control pseudo-instructions indicate to the Assembler the radix to be used in number interpretation.

The pseudo-instruction DECIMAL indicates that all numbers are to be interpreted as decimal until

the next occurrence of the pseudo-instruction OCTAL.

The pseudo-instruction OCTAL indicates that all numbers are to be interpreted as octal until the next occurrence

of the pseudo-instruction DECIMAL.

otherwise specified

The radix is initially set to octal and remains octal unless

3—2

Symbol
Any sequence of letters and digits beginning with a letter and delimited by punctuation characters is a

symbol. Although a symbol may be any length, only the first six characters are considered, and any ad—
ditional characters are ignored; symbols which are identical in their first six characters are considered

identical. Pseudo Instructions may not be used as symbols or tags within a program.
The Assembler has in its permanent symbol table definitions of the symbols for all PDP-8 operation codes,

operate commands, and many IOT commands (see the Appendix for a complete list).

These may be used

without prior definition by the user.

Examples:
is a symbol whose value of 4459“ is taken from the operation code

JMS

definitions.

When used as a symbolic address tag,
This value is

is a user-created symbol.

its value is the address of the instruction it tags.

assigned by the Assembler.

PARAMETER ASSIGNMENTS
A parameter may be assigned by use of the equal

sign.

The symbol to the left of the equal sign is assigned

the value of the expression on the right.

Examples:
A=6

EXIT=RETURN=JMP l 13

Symbols defined by use of the equal sign may be used in any valid expression.
Example;

A=lfl¢
B=4fl¢
has the value 59¢

A+B

has the value Hg,“

TAD A

If the expression to the left of the equal sign has already been defined, the ReDefinition diagnostic:
RD

XXXXXX

dddd

Will be typed where XXXXXX is the symbol's name and dddd is the contents of the current location
counter at

the point of redefinition.

The new value will be stored in the symbol table.

3-3

Example:

1W
CLA=76¢¢

will cause the diagnostic:
RD

CLA

Whenever CLA is used after this point, it will have the value 76ml.

SYMBOL DEFINITION

by the user in one of two ways

A symbol may be defined

(I) by use of parameter assignment
Example:
DISMIS=JMP l g
and

(2) by use of the comma

When a symbol is terminated by a comma, it is assigned a value equal to the current location counter.
If it is defined more than once in this manner, the Assembler will type the duplicate tag diagnostic:
DT

XXXXXX

dddd

where XXXXXX is the symbol, and dddd is the current location counter at the second occurrence of the

attempted symbol definition.

The symbol is not redefined.

Example:

*35595
START,

TAD A
DCA COUNTER

CONTIN,

JMS LEAVE
JMP START

A,
COUNTER,
START,

-74

fl
CLA CLL

The symbol ”START" would have a value of fiBflfl, the symbol "CONTlN" would have a value of $332,
the symbol "A" would have a value of fl3fl4, the symbol "COUNTER" (considered by the Assembler to be

COUNTE) would have a value of 3213;55, and when the Assembler processed the next line, it would type
during PASSl:
3—4

S TART

flSflé

Since the first PASS of PAL lll is used to define all
a

symbols in the symbol table, the Assembler will type

diagnostic if, at the end of PASSl, there are any symbols remaining undefined.

For example:

*71713
TAD C

CLA CMA
HLT
JMP Al

C,¢
$
would produce the Undefined Address diagnostic:
UA

XXXXXX

dddd

where XXXXXX is the symbol and dddd is the location at which it was first seen.
is printed at the end of PASS]

The entire symbol table

In the case of the above example, this would be:

717g

7174

7173

If, during PASS], PAL lll detects that its symbol table is full (in other words, that there is no more memory
space to store symbols and their associated values), the Symbol Table full diagnostic:
ST
is typed.

XXXXXX

dddd

XXXXXX is the symbol that caused overflow, and dddd is the current location when the over—

The Assembler halts and may not be restarted.

flow occurred.
or more

The source program should be segmented,

address arithmetic used, to reduce the number of symbols.

Using ASR33; 655 symbols.
defined symbols.

PAL lll's symbol

capacity is:

The basic symbol table contains 65 symbols (see Appendix) leaving 59¢ user-

Using the High-Speed Reader; 56g symbols. The basic symbol table contains 65

symbols leaving 495 user—defined symbols.
EXPRESSIONS

Symbols and numbers are combined with certain operators to form expressions.
+

I_l

There are three operators;

plus

this signifies 2's complement addition

minus

this signifies 2's complement subtraction

space

space is interpreted in context. Since a PDP—8 instruction has an operation code of three bits as well as an indirect bit, a page bit, and seven

address bits, the Assembler must combine memory reference instructions
3-5

in a manner somewhat different from the way in which it combines operate
or

[CT instructions.

The Assembler accomplishes this by differentiating

the symbols in its permanent symbol table. The following symbols are
used as memory reference instruction op codes;

figflfl
lflflfl
ZWJfl
3flf5fl
4528535
5am

AND
TAD

lSZ
DCA
JMS
JMP

lflflfl
2¢¢¢
3151M
415W
5km
éflflfl
7%39'
55555555

FADD
FSUB
FMPY
FDIV

FGET
FPUT

FNOR
FEXT

logical AND
Two's complement ADdition
Index and Skip if Zero

Deposit and Clear Accumulator
JuMp to Subroutine
JUMP

Floating ADDition
Floating SUBtraction
Floating MultiPlY
Floating DIVide
Floating GET
Floating PUT
Floating NORmalize
Floating EXiT

When the Assembler has processed one of these symbols, the space acts as an address field delimiter:

MUM/I
A

JMP
CLA

A has the value 41m, JMP has the value 512%, and the space acts as a field delimiter.
are

These symbols

combined as follows:
A

JMP

1W W1 33W 91151
W“ Wfl W3 M5

The seven address bits of A are taken, i.e.:

13W 155?“ Ml Wt
The remaining bits of the address are tested to see if they are zero's (page zero reference); if they are not,
the current page bit is set:

12W 1511 PW $3951
The operation code is then ORed into the expression to form:

U151 55“ 95W 553?“
or, written

concisely:

53¢]

3-6

In addition to the above outlined tests, the page bits of the address field are compared with the page bits
of the current location counter.

If the page bits of the address field are nonzero and do not equal the page

bits of the current location counter,

out-of—page reference is being attempted and the Illegal Reference

diagnostic is printed on PASSZ or PASS3.
For example:

*4iflfl
A,

CLA CLL

*72w'
JMP A

The symbol in the address field of the jump instruction has a value of4l¢¢ while the current location
counter, i.e., the address where the instruction will be placed in memory, has a value of 72%].
instruction is illegal on the PDP—8 and will be flagged during PASSZ or PASS3 by the

This

Illegal Reference

diagnostic:
IR

4i¢¢

72¢fl

The value 53¢¢ would be assembled at location 722%.

The symbol I caused the indirect bit (bit 3) to be set in a memory reference instruction:
DCA

For example:

19'

would produce:

1955?!

or:

341g
When a space occurs in an expression that does not contain a memory reference instruction op code, it
means

inclusive OR:

For example:

CLA

CLL

the symbol CLA has a value of 73315 and the symbol CLL has a value of 719% CLA CLL would produce 73%.
User-defined symbols are treated as nonmemory reference instructions (see Pseudo-Instructions).

3-7

For example:

A=333
*222

B, CLA
Then the expressions and their values are shown below;

Al—lB

¢555
m11
¢333

—A

7445

A+B
A—B

1-3

7557

3-1

{21221
77157

—7l
etc

An expression is terminated

by either a carriage—return () ) or a semicolon (;).

If any information was

generated to be loaded, the current location counter is incremented.

Example:
RAR; RTR;

CMA)

Produces three registers of information and the current location counter is incremented after each ex—

pression

The statement:
HALT=HLT

CLA)

produces no information to be loaded (it produces an association in the Assembler's symbol table) and
hence does not increment the current location counter.
*4721

TEMP, )

TEM2, g)
The current location counter is not incremented after the line
and TEM2 are assigned the same value, in this case 472i

TEMP,) and hence the two symbols TEMP

CURRENT ADDRESS INDICATOR

The single character period (.) has,

It may be used as any number or symbol

all times,

value equal to the value of the current location counter.

(except to the left of the equal sign).

Example:

*2!”
J MP

+2
3—8

is equivalent to
*

JMP 2,62.

3%
,+24£M

would produce, in register 3flfl, the quantity 27¢¢

Example:

*ZZWJ
CAL L=J MS 1
27

Since the second

line, CALL=JMS l

does notincrement the current location counter,

flfl27 would be

placed in register 221313 and CALL would have the value of lflfl ilfl flflfiz or 46i5i38.
The properties of the character (.) have been slightly changed;

Previously,

PAL III would neither diagnose nor correctly assemble

there is no space between the P and the.)

that,

it now acts as a terminator.

expressions such as:

JMP.

(where

PAL III now treats this (JMP.) as it it were this (JMP

COMMENTS
A comment field is indicated

by the slash (/) character. The Assembler will ignore everything from

the slash to the next carriage return

Example:
CLA

/THIS IS A COMMENT
PSEUDO-INSTRUCTIONS

There are several pseudo-instructions that are used to direct the Assembler.
DECIMAL

Set the current radix to decimal

OCTAL

Set the current radix to octal

PAUSE

These are:

Stop the Assembler. The current pass is not terminated. PAUSE must be
physical end of the program tape as the reader routines are buffered
and the buffer is emptied when PAUSE is detected. The assembly is continued by depressing CONTINUE. Two or more tapes must be used with
at the

the PAUSE instruction.
FIELD

Causes a field setting to be punched during PASSZ.

This is recognized by

the Binary Loader (DEC-O8-LBAA-PM) and causes all subsequent information to be loaded into the field specified by the expression. The expression must be between fl and 7, inclusive.
EXPUNGE

Erase the entire symbol table except for the pseudo-instructions.

FIXTAB

Fix the current symbol table.

printed

Symbols that have been fixed are not

in the symbol table at the end of PASSI

3-9

PASS3.

Fix memory reference instruction

FIXMRI

This may be given only after

It tells the Assembler that the following symbol definition

EXPUNGE.

is a memory reference instruction and is to be treated as described under

Expressions

Example:
EXPU NGE

FIXMRI TAD=1¢¢¢
FIXMRI DCA=3M25

CLA=72¢125
FIXTAB
PAUSE

When this program segment is read into the Assembler during PASSl, all symbol definitions are
deleted and the three symbols listed are added to the table.

This process is often performed to alter the Assembler's symbol table so that it contains only those

symbols that will be used

This may increase the Assembler's capacity for other user-defined symbols.

Symbolic representation for indirect addressing

Example:
DCA I STORE

Optional method of denoting a Page fl reference.

Example:
DCA Z ADD

CHAPTER
PROGRAM

PREPARATION

AND ASSEMBLER

OUTPUT

The source language tape (symbolic tape) is prepared in ASCII code on 8-channel punched paper tape

using an off-line Teletype or the on-line Symbolic Tape Editor (DEC-08-ESAB-D).
should begin with leader code which may be blank tape, code 2%],

In general, a program

rubouts.

PROGRAM TAPE
Since the Assembler ignores certain codes, these may be used Freely to produce a more readable symbolic
source

tape.

These codes are tab, line-feed, and form-feed.

The Assembler will also ignore extraneous spaces,
tape

carriage-return/Iine-feed combinations, and blank

The program body consists of statements and pseudo-instructions.

sign Followed by some trailer code.
instruction PAUSE.

The program is terminated by the dollar

It the program is large, it may be segmented by use of the pseudo-

This often facilitates the editing of the source program since each section will be

physically smaller.
The Assembler initially setsits current location counter toflZflQ’. Thisis reset whenever the asterisk is processed.

During PASSI, all illegal characters cause a diagnostic to be printed.
The following two programs are identical:

*ZW
/EXAMPLE OF FORMAT
/GENERATOR
BEGIN, fl/START OF PROGRAM
KCC

KSF/WAIT FOR FLAG
JMP.-I/FLAG NOT SET YET
KRB/READ IN CHARACTER
DCA CHAR
TAD CHAR

TAD MSPACE/IS IT A SPACE?
SNA CLA

HLT/YES
JMP BEGIN+2 /NO: INPUT AGAIN

CHAR, fl/TEMPORARY STORAGE
MSPACE, -24¢/—ASC|I EQUIVALENT

/END OF EXAMPLE
$

The character is ignored.

*ZW
/EXAMPLE OF FORMAT
/GENERATOR
BEGIN,
I5

/START OF PROGRAM

KCC

/WAIT FOR FLAG
/FLAG NOT SET YET
/READ IN CHARACTER

KSF

JMP.—I
KRB

DCA CHAR
TAD CHAR
TAD MSPACE

/IS IT A SPACE?

SNA CLA

/YES

HLT

JMP BEG|N+2 /NO: INPUT AGAIN

CHAR,
MSPACE,

y!
-24IJ

/TEMPORARY STORAGE
/-ASCII EQUIVALENT

/END OF EXAMPLE
$
Both of These programs are identical and produce the same binary code.
To

read

The second, however, is easier

During PASSl, the Assembler reads the source tape and defines all symbols used.

If any symbols remain undefined, The UA diagnostic is

is printed

(or punched) at The end of PASSl

printed.

The symbol Table is printed in alphabetic order.

The user's symbol Table

If The program listed above were assembled,

The PASSl output would be:
BEGIN
CHAR
MSPACE

may}
91213
gm 4

During PASSZ, The Assembler reads The source Tape and generates The binary code using The symbol Table

equivalences defined during PASSl

The binary Tape that is punched may be loaded by the Binary Loader

(DEC-08— LBAA-PM). This binary Tape consists of leader code, on originsetting, and Then daTa words. Every
occurrence

of an asterisk experssion causes a new origin to be punched on The Tape and resets The A5-

sembler's current location counter.
and trailer code is generated.

AT the end of PASSZ, The checksum is punched on the binary tape

During PASSZ, The Assembler may diagnose an Illegal Reference. When

using The ASR33 Punch, The diagnostic will be both typed and punched and will be preceded and followed

by rubouts.

The Binary Loader will ignore everything that has been punched on a tape between rubouts.

During PASS3, The Assembler reads the source Tape and generates the code from The source statements.
The assembly listing is Typed (or punched).
code in octal, and the source statement.

It consists of The current location counter, the generated

The symbol table is Typed at the end of the pass.

listed above were assembled, the PASS3 output would be:

4—2

If The program

MW
9525?“
152132
M213
152134
$52555
132136
112137
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/EXAMPLE OF FORMAT
/GENERATOR
BEGIN,
I?!

/WAIT FOR FLAG
/FLAG NOT SET YET
/READ IN CHARACTER

KSF

JMP.—I
KRB

321 3

DCA CHAR

121 3

TAD CHAR

1 21 4

TAD MSPACE

765g
7432
521212
WW
7545

SNA CLA
HLT
JMP BEGIN+2

CHAR,
MSPACE,

I?!
-24;25

/END OF EXAMPLE
BEGIN
CHAR

MSPACE

/START OF PROGRAM

KCC

£32911?!
I52} 3
£3214

4-3

/IS IT A SPACE?
/YES
/NO: INPUT AGAIN
/TEMPORARY STORAGE
/—ASCI| EQUIVALENT

CHAPTER

OPERATING

INSTRUCTIONS

The PAL III Assembler is provided as a binary tape.

This is loaded into the PD-P-8 memory by means of

the Binary Loader, using either the ASR33 Reader or the High-Speed Reader (see DEC-08—LBAA—D).

The Assembler will use either the ASR33 Reader or the high—speed reader to read the source language

tape, and it will use either the ASR33 Punch or the High-Speed Punch for output.
devices is made by the Assembler when it is started.

The selection of I/O

The source language tape must be in the proper

reader, with the reader and punch turned on. When using the high-speed punch, the symbol table will
be typed on the ASR33 if bit ll of the switch register is 0 (down); it will be punched on the high—spped

punch if bit ll of the switch register is a I (up).

When using the high-speed punch, the symbol table

output, the telepunch should be left on, since the symbol table produced

may be read by DDT (see

DEC-08-CDDA-D). All diagnostics will be typed on the ASR33 (except for the undefined address diagnostic when using the high-speed punch and the bit ll switch option).

PASSZ will be punched using the ASR33

The binary tape produced during

punch or the High-Speed Punch if it is included in the machine

configuration and turned on. The only diagnostic in PASSZ will be Illegal Reference. Since this is

typed on the ASR33, it may also be punched on the binary tape.

It will, however, be

Binary Loader. The bit ll switch option may be used during PASS3 also.

ignored by the

If the machine is not equipped

with a High-Speed Punch, bit II will have no effect.
In addition to the binary tape of the Assembler, the user is provided with an ASCII tape containing sym-

bol definitions for the instruction sets of the available options to the PDP-8 (i .e. , card readers, magnetic tapes,

A/D converters).

Since there is only a finite amount of space available, expanding the

number of permanent symbols that the Assembler recognizes decreases the maximum number of symbols
the user may have available
to contain definitions for

For this reason, the ASCII Extended Definitions tape should be edited

only those options which the user has acquired.

the Assembler only on PASSI

This tape should be read into

Since it permanently fixes the symbols it contains, it should not be read

again until PAL III is reloaded.
l

Load the Assembler using either the ASR33 Reader or the

Set JUZJZM into the switch register; press LOAD ADDRESS

Place the source language tape in the reader.

High—Speed Reader.

Turn the reader on; turn the punch on.

Set Bits I? and ] of the switch register for the proper pass.
Bit 121

Bit 1

]

PASS]

]

PASSZ

]

PASS3

These settings are:

PASS] is required so that the Assembler can initialize its symbol table and define

all user symbols.
5.

After PASS] has been made, either PASSZ or PASSB may be made.

Bit ]] switch option

During PASS] Bit ]]

Punch symbol table on high—speed punch if it isinthe

]

machine configuration.
Bit ]]

Type (and punch) the symbol table on the ASR33.
No effect

During PASS2
During PASS3 Bit ]]

Punch assembly

punch
Bit ]]

Press START.

=¢

listing tape,

ASCII,

high-speed

Type assembly listing on ASR33.

The Assembler will halt at the end of each pass.

Proceed from step 3.

If the Assembler has halted because of a PAUSE statement, put the next tape into the
reader and press CONTINUE.

SUMMARY

PASS]

The Assembler reads the source tape, defines all user symbols, and outputs the user

symbol table in alphabetic order.
lC

dddd

PASS]

diagnostics are:

Illegal Character

XXXX

where dddd is the value of the illegal character and xxxx is the value of the current

location counter when the character was processed.

XXXXXX

dddd

The character is ignored.

ReDefinition

where XXXXXX is the symbol being redefined and dddd is the value of the current
location counter at the point of redefinition.

xxxxxx

dddd

Duplicate Tag

5—2

The symbol is redefined.

An attempt is being made to redefine a symbol using the comma.

XXXXXX is the

symbol and dddd is the value of the current location counter. The previous value of
the symbol is retained and the symbol is not redefined.

XXXXXX

dddd

Symbol Table full

where XXXXXX is the symbol causing the overflow and dddd is the value of the Current Location

restarted

Counter at the point of overflow.

The Assembler halts and may not be

XXXXXX

dddd

Undefined Address

where XXXXXX is the symbol that was used, but never defined, and dddd is the value
of the Current Location Counter when the symbol was first processed.

with the symbol table at the end of PASS]

This is typed

The symbol is assigned a value equal to

the highest address on the memory page where it was first used.
PASSZ

The Assembler reads the source tape and using the symbol table defined during PASSl,
generates and punches the binary code.

Binary Loader.
IR

dddd

This binary tape may then be loaded by the

The PASSZ diagnostic is:

Illegal Reference

xxxx

where dddd is the address being referenced and xxxx is the value of the Current
Location Counter.

The illegal address is then treated as if it were on the proper mem—

ory page.

Example;

*73g6
JMP

3217

would produce:
lR

53397

73¢6

and would generate 53117 to be loaded into location 73156.

5-3

PASSB

The Assembler reads the source tape and, using the symbol table defined during PASSl
generates and types the code represented by the source statements.
tion

line.

Counter, the contents,

and the source statement are typed side

The Current Loca—

by side on one

If bit ll of the switch register is a l and the machine configuration includes

the high-speed punch, the assembly listing will be punched in ASCII.

diagnostic is Illegal Reference.

5—4

The PASS3

CHAPTER

SYMBOL

ALTERATION

TABLE

PAL III contains a table of symbol definitions for the basic PDP-8 and its most common optional

devices.
gram

These are the symbols such as TAD, RFC or SPA, which do not have to be defined in every pro-

This table is considered to be PAL III's permanent symbol table.

listed under the heading BASIC SYMBOLS in Appendix I of this manual.
more

peripheral

All the symbols it contains are
If the user had purchased one or

of the optional devices whose instruction set is not defined among the BASIC

SYMBOLS, for example,

EAE or an A/D CONVERTER, it would be desirable if he could add the necessary symbol definitions to the

This would eliminate the need for him to define these symbols in every program

permanent symbol table.
he writes.

The opposite case would be the user who needs more space for his symbols.

He would like to be

able to delete all definitions except the ones he will actually use in his program.

For such purposes PAL III has three

table.

pseudo-instructions that may be used to alter its permanent symbol

These pseudo-instructions are recognized by the Assembler only during PASSI

PAS$2 or 3,

During either

they are ignored and have no effect.

The pseudo-instructions that alter the symbol table are:
EXPUN GE

Erase the entire permanent symbol

table, except for the 9 pseudo-instructions

listed in Appendix I under BASIC SYMBOLS.

FIXMRI

Fix Memory Reference Instructions.
a

This must be followed on the same line by

symbol definition statement (parameter assignment) since the memory reference

instructions are constructed in the symbol

instructions.

immediately following the pseudo-

In other words the letters FIXMRI must be followed by one space,

the symbol for the MRI to be defined,

equal sign, and the actual value of the

symbol to the immediate left of the equal sign. The pseudo-instruction must be
repeated for each MRI to be defined
definition of any other symbol.

EXAMPLE:

EXPUNGE
FIX MRI

TAD

1000

FIX MRI

DCA

3000

All MRI's must be defined before the

FIX the current symbol TABLE

FIXTAB

occurance

All symbols that have been defined before the

of this pseudo-instruction are made part of the permanent symbol table

and will not be printed in the symbol table at the end of PASSl

PASS3.

An actual tape to add two symbols to those already in PAL III's permanent symbol table would have punched
on

it in ASCII:

CDF=62¢T
C IF=62¢2
FIXTAB

PAUSE

To use such a tape the user would:
I

Read in PAL III with the Binary Loader.

Set 200 in the SWITCH REGISTER and press LOAD ADDRESS.

Set switches for PASSl

Put definitions tape

Press START

(ASCII) in the proper reader.

The PAUSE pseudo-instruction at the end of the tape indicates to the Assembler that the current PASS is
not ended and

another tape is to follow

With switches still set to PASSl, put user's program in reader and press CONTINUE on the
console

The next program to be assembled should not be preceded by the definitions since they are already in the

permanent symbol table and will be there until PAL III is reloaded.
After altering the symbol table to fit his needs the user might wish to keep PAL III in this state.

be done by punching a binary of the section of core occupied by PAL with its new symbol table

This can
.

To do this:
i

Read in PAL III and modify symbol table as desired.
PAL III's symbol table

table

begins at location 23508.

Count all the symbols in the

Since each symbol and its value require four registers,

Convert this number to octal and add it to

The lower limit is OOOl

6-2

altered symbol

multiply this number by 4.

23508. This number is the upper limit of PAL III

Using the directions for Binary Punch Routine.

(Digital—8-5-U) and the

limits

stated in 2

above punch out the PAL III Assembler itself.
4.

The output of the Binary Punch Routine is the Assembler with the modified Symbol Table and
may be loaded with the binary loader.

PAL III is loaded.

EXAMPLE:

The following ASCII tape is read in on PASS] :
CDF
CIF
RDF
RIF

6202
6214

RMF
RIB

6201

6224
=

6244

6234

FIXTAB
PAUSE

The Assembler now has in its symbol table the "MEMORY EXTENSION CONTROL" symbols and
definitions.

Six symbols were added and none removed

There were 84 symbols in the basic

Assembler, there are now 90 symbols which require a total of 360
the symbol table starts at 2350, it extends to
Routine is used to punch from

23508 5508

(10)

3l208

550

locations.

Since

The Binary Punch

000i8 through 3l20 8 and the output is the Assembler with all the

basic symbols plus memory extension symbols.

APPENDIX

SYMBOL

LISTS

BASIC SYMBOLS

/PSEUDO INSTRUCTIONS
FIELD
EXPUNGE
FIXMRI
PAUSE
FIXTAB
DECIMAL

OCTAL
I
z

/MEMORY REFERENCE INSTRUCTIONS
AND
WW
TAD
1mg
IS-Z
2mg
DCA
3mg
JMS
4mm
JMP
5mg

/FLOATING-POINT INSTRUCTIONS
FEXT
WW
FADD
Iggy!
FSUB
212W
FMPY
3mg
FDIV
4W9!
FGET
5mm
FPUT
6mm
FNOR
715W

/PROGRAM INTERRUPT
6W1
éflm
/H|GH-SPEED READER
RSF
69!“
RRB
69112
6% I4
ION
IOF

/H|GH—SPEED PUNCH
PSF
PCF
PPC
PLS

@2121
6¢22
652524
6,626

/KEYBOARD/READER
KSF
6¢31
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6¢32
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6¢36

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6344

/GROUP I OPERATES
NOP
IAC
RAL
RTL
RAR
RTR

CML
CMA
CLL
CLA

/GROUP 2 OPERATES
HLT
74m
OSR
74PM

646

713W
7W1
7W4
7¢¢6
7mg
7¢I2
7mg
7¢4¢
7mg
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/COMBINED OPERATES
CIA
LAs

Al—l

7¢4I
76¢4

74142!
742421
7432
74421
74521
75m
751 g

SKP
SNL

SZL
SZA
SNA
SMA
SPA

STL
GLK
STA

712$
72214
724g

/DECTAPE DUAL TRANSPORT TYPE 555 AND CONTROL TYPE 552
MMMM

6757

MMSF

6761

MMMF

6756

MMCF

6772

MMML

6766

MMSC

6771

MMLS

6751

MMRS

6774

MMLM

6752

MMCC

6762

MMLF

6754

MMLC

6764

/DECTAPE TRANSPORT TYPE TU55 AND CONTROL TYPE Tcm
DTRA

6761

DTSF

6771

DTCA

6762

DTRB

6772

DTXA

6764

DTLB

6774

/MEMORY PARITY TYPE 188
SMP

61 m

CMP

61 T214
EXTENDED SYMBOLS

/PDP -5 EAE SYMBOLS 153*

LAR

6W1
61132
61,64

MUL

6111

RDA

6112

CAM

LMQ

SZO

6114

DIV

6121

RDM

6122

SAF

6124

/PDP—8 EAE SYMBOLS 182

7M5
7427

ASR

7415

DVI

LSR

7417

NMI

7411

MQL

7421

SHL

7413

SCA

7441

MQA

75W

CAM

7621

MUY

/MEMORY EXTENSION CONTROL TYPE 183
62,01
6222

RIF

6224

CIF

RMF

6244

RDF

6214

RIB

6234

CDF

/AUTO RESTART TYPE KR¢1
SPL
*

6122

PDP—5 EAE symbol definitions do not appear on the actual

tape due to a conflict in the CAM
instructions of PDP—5 and PDP-8. PDP-8 EAE
symbols should be deleted if those for PDP-5 are
inserted in the extended symbols tape.

A1 —2

/AD CONVERTER TYPE 189
ADC

6fl¢4

/AD CONVERTER/MULTIPLEXER T38E/T 39E
ADSF

653T

ADCC

ADCV

6532

ADSC

65 42

ADRB

6534

ADIC

65 44

DYL

DYS

6¢63
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6¢64
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DCF

6572

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DCX
DXL

DC Y

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6155]
6¢53
6¢61
62557

DIX

DIY

/SCOPE TYPE 3ON
DLB

612574

/LIGHT PEN TYPE 37¢
DSF

61671

/PLOTTER AND CONTROL TYPE 35EB

65m
65¢4

PLCF

65m

PLPU

PLPR

65]]

PLPU

6512

PLDD

6514

PLPL

6521

PLUD

6522

PLPD

6524

PLSF

/CARD READER AND CONTROL TYPE CRWC
RCSF

663]

RCSP

667 T

RCRA

6632

RCSE

667]

RCRB

6634

RCRD

6674

/CARD READER TYPE 451
CRSF

6632

CERS

6634

CRRB

667T

CRSA

6672

CRSB

6674

CPSE

6642

/also services card punch 450

/CARD PUNCH AND CONTROL TYPE 45¢
CPSF
CPCF

663T
664]

CPLB

6644

/CERS

appears under card reader 451

/LINE PRINTER TYPE 645
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6652

LPR

6655

LSF

6661

LCB

6662

LLB

6664

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