Computer Hardware

Spectra 70

RCA Spectra 70 Training Manual

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EXTRN

CODE

Reference

to

a

symbol

in

another

program

is

defin-

ed

by

the

EXTRN

Code.

A

separate

statement

must

appear

for

every

symbol

appearing

in

another

pro-

gram.

EXTRN

appears

in

the

OPERATION

field

and

a

symbol

must

be

used

in

the

OPERAND

field.

The

NAME

field

is

not

used

on

this

line.

EXAMPLE

OF

ENTRY

AND

EXTRN

One

use

of

the

ENTRY

and

EXTRN

codes

is

to

link

a

program

to

a

subroutine.

Assume

that

a

SINE-CO-

SINE

subroutine

has

two

ENTRY

points;

SINE

and

COS,

and

one

EXTRN

point;

RTN.

Programs

using

the

SINE-COSINE

routine

can

BRANCH

to

either

SINE

or

COS

depending

on

which

function

is

to

be

computed.

The

SINE-COSINE

routine

BRANCHES

to

RTN

after

computing

the

function.

SINE-COSINE

ROUTINE

NAME

OPERATION

OPERAND

SINE

COS

START

ENTRY

EXTRN

B

B

END

COS

RTN

RTN

RTN

MAIN

PROGRAM

NAME

OPERATION

OPERAND

BGN

RTN

START

ENTRY

EXTRN

B

END

RTN

COS

~COS

is

an

ENTRY

COS

point

in

the

SINE-

COSINE

Routine

The

main

program

defines

RTN

as

an

ENTRY

point

that

allows

the

SINE-COSINE

routine

to

BRANCH

to

RTN.

20

RUN

AND

SEGMENT

CONTROLLING

CODES

The

first

and

last

statements

of

the

source

program

must

be

a

START

and

END

statement,

respectively.

If

a

program

contains

sections

which

are

to

be

load-

ed

individually,

the

second

and

succeeding

sections

must

begin

with

a

CSECT

control

code.

START

CODE

In

addition

to

flagging

the

start

of

the

source

pro-

gram,

a

START

code

can

set

the

location

counter

to

an

initial

value

and

identify

an

entry

into

the

pro-

gram.

START

must

appear

in

the

OPERATION

field.

A

self-defining

value,

written

in

the

OPERAND

field,

sets

the

location

counter.

A

symbol

appearing

in

the

NAME

field

is

considered

an

ENTRY

point

into

the

program

(see

ENTRY

code).

NAME

OPERATION

OPERAND

BEGIN

START

END

CODE

S'064'

Set

Location

counter

to

100(10)'

Establish

"BEGIN"

as

an

entry

point.

The

END

code

informs

the

Assembler

that

all

source

input

statements

have

been

processed.

The

OPER-

AND

field

specifies

the

starting

address

of

the

object

program.

A

symbol,

self-defining

value,

or

aster-

isked

address

may

appear

in

the

OPERAND

field.

NAME

OPERATION

OPERAND

END

CSECT

CODE

STARTP

STARTPisthe

name

of

the

pro-

gram

starting

address

The

CSECT

code

identifies

both

the

beginning

of

a

new

section

(segment)

and

the

termination

of

the

pre-

vious

section.

The

START

code

identifies

the

first

section,

therefore

CSECT

should

be

used

for

the

second

and

succeeding

sections

only.

The

NAME

field

may

contain

a

symbol

or

be

left

blank.

A

sym-

bol

used

in

one

segment

can

be

referenced

by

any

other

segment

in

the

program.

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Reference Manual260 pages

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RCA Spectra 70 Specifications

General

Brand	RCA
Model	Spectra 70
Category	Computer Hardware
Language	English

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