Computer Hardware

Spectra 70

RCA Spectra 70 Training Manual

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BRANCH

ON

COUNT

INSTRUCTION

This

instruction

allows

a

program

to

loop

through

a

routine

a

given

number

of

times.

A

general

register

holds

the

count

of

the

number

of

times

the

loop

is

to

be

executed.

Each

time

the

Branch

on

Count

is

executed,

the

register

is

decremented

by

one

(binary

count).

When

it

has

been

decremented

to

zero,

the

branch

address

is

ignored

and

the

next

se-

quential

instruction

is

executed.

Example:

In

the

following

section

of

a

program

the

routine

EDTB

is

to

be

executed

seven

times

before

proceeding

on

to

the

next

routine

CONT.

NAME

OPERATION

OPERAND

~

~

EDTB

(

)

I

BCT

9,EDTB

CONT

t

J

Prior

to

entering

the

routine

(EDTB),

General

Reg-

ister

9

was

loaded

with

a

binary

value

of

six

(see

LOAD

MULTIPLE

Instruction

in

this

section).

The

routine

(EDTB)

is

executed

once

and

repeated

the

number

of

times

specified

by

the

binary

count

in

General

Register

9.

When

the

count

is

decremented

to

zero

the

Branch

Address

is

ignored

and

the

next

sequential

instruction

(CONT)

is

executed.

SET

P2

REGISTER

(STP2)

INSTRUCTION

This

instruction

transfers

control

from

the

Interrupt

State

to

the

Processing

State.

It

sets

the

P2

Register

with

the

desired

value

and

transfers

to

the

address

contained

in

the

PI

Register

(Reserved

Locations

40

and

41).

The

Condition

Code

Indicator

is

also

reset

to

the

Con-

dition

Code

that

existed

at

the

time

the

Processing

State

was

interrupted.

In

addition,

the

hardware

in-

terrupt

register

is

reset

by

the

interrupt

mask

in

reserved

memory.

39

Example:

Assume

the

following

values

are

stored

in

HSM

im-

mediately

before

execution

of

the

instruction,

HEM

BEFORE

EXECtTTION

PI

COL~'TER

P2COL":-;TER

and

that

ENTR

had

been

assigned

a

value

of

3800

10

by

the

Assembler.

The

following

instruction

transfers

control

to

the

PI

state,

and

stores

3800

10

in

the

P2

counter.

ASSEMBLY

INSTRUCTION

GENERATED

INSTRUCTIOK

HSM

AFTER

EXECUTION

Exercise:

OPERATION

STP2

OP

M

00

3800

10

I

General

Register

one

contains

0000

PI

Counter

P2

Counter

40

41

44 45

00

00

2300

10

3800

10

TRANSFER

CONTROl:,

TO

2300

10

CODE

RESET

TO

3

USing

the

memory

layout

above,

indicate

which

Con-

dition

Code

would

be

set

after

execution

of

the

fol-

lowing

instructions.

COMPARE

DECIMAL

OPERATION

OPERAND

1

CP

BAL

(3), UNIT + 1

(2)

2

CP

VAL

(3), COST

(3)

3

CP

AMT (3), NUM

(4)

CONDo

CODE

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RCA Spectra 70 Specifications

General

Brand	RCA
Model	Spectra 70
Category	Computer Hardware
Language	English

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