IBM 7090 - Transfer Instructions

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The

E

cycle

is

used

to:

1.

Reset

the

MQ

2.

Bring

the

divisor

from

storage

3.

Set

338 (2710)

into

the

SC

(used

to

count

the

number

of

shifts

during

divide)

4.

Divide

dividend

fraction

by

2

by

shifting

the

fraction

right

one

place

(to

be

used

for

comparison

of

dividend

fraction

to

divisor

fraction)

First

step

L

time

is

used

to:

1.

Determine

if

dividend

fraction

is

more

or

less

than

two

times

the

divisor

fraction

2.

Set

the

MQ(S)

to

the

algebraic

sign

of

the

quotient

3.

Shift

dividend

left

one

place

to

put

dividend

back

to

initial

position

4.

Check

AC

fraction

for

zero

5.

Get

the

difference

between

divisor

and

dividend

characteristics

6.

End

operation

if

the

AC

fraction

is

zero

or

if

the

dividend

fraction

is

twice

as

large

or

larger

than

the

divisor

fraction

7.

Reset

the

whole

AC

if

the

AC

fraction

is

zero

Second

step

L

time

is

used

to:

1.

Increase

the

characteristic

difference

by

one

if

dividend

fraction

is

equal

to

or

greater

than

the

divisor

fraction

2.

Shift

the

dividend

fraction

left

one

place

if

the

dividend

fraction

is

less

than

the

divisor

fraction

3.

Step

the

shift

counter

down

to

2610--the

desired

number

of

shifts

to

move

a

bit

from

MQ(35)

to

MQ(9).

Third

step

L

time

is

used

to

do

the

actual

division.

The

objectives

of

third

step

L

time

are

to:

1.

Attempt

to

reduce

the

AC

fraction

by

the

amount

of

the

divisor

fraction

2.

If

the

reduction

is

successful

put

a 1

in

MQ(35)

3.

Shift

AC

and

MQ

left

one

place,

step

shift

counter,

and

put

a 1

in

AC(35)

4.

Repeat

steps

1,

2,

and

3

until

the

SC

equals

zero

5.

Compute

the

characteristic

of

the

quotient

and

put

it

into

the

MQ

6.

End

operation

when

the

shifting

and

reductions

are

complete

I

time

of

the

next

instruction

is

used

to:

1.

If

there

was

no

divide

check

and

the

dividend

fraction

was

not

zero:

a.

AC

fraction

is

re

-complemented

to

get

true

number

b.

Characteristic

of

the

remainder

is

set

to

2710

less

than

the

original

characteristic

of

the

dividend

2. Stop

the

machine

if

there

was

a

divide

check

Floating

Divide

or

Proceed

FDP

+0241 (Min

I,

E,

L)

(Max

I,

E,

12L)

This

instruction

operates

the

same

as

FDH,

except

that

a

divide

check

does

not

halt

the

computer.

5.3.05

Transfer

Instructions

Transfer

instructions

are

used

to

alter

the

sequence

of

instructions.

The

condi-

tional

transfers

allow

automatic

testing

of

problem

conditions

without

stopping

the

91

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