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INTERRUPT CONTROLLER

Register), is as

detailed

below.

The

address

location

OCW2

is

written

to,

is

OOH

within

the

I/O

space.

OCW3

is

a

command

word

which

provides

more

facilities

to

alter

the

priority

of

the

interrupt

request

lines,

and

also

allows

the

status

of

two

internal

registers

within

the

PIC,

the

Interrupt

Request

Register

(IRR)

and

the

Interrupt

Service Register

(ISR),

to

be checked. Facilities for altering

the

priority

of

the

interrupt

request

lines

are

not

required as

explained above.

To

read

either

of

the

two

registers requires

two

operations

to be carried

out;

a

write

operation

using

OCW3

to

select

the

register; followed by a read

operation

to

access

the

data

within

the

register.

The

format

of

OCW3

to

select

the

registers is detailed below.

The

address

location

of OCW3 is

OOH

within

the

I/O

space.

The

address location,

the

register

data is read

from

is also

OOH

within

the

system

input/

output

space.

I x I 0 I 0 I 0 I 1 I 0 I 1

IRIsl

OCW3

1 -

Read

ISR

1...-------1

0 _

Read

IRR

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Other manuals for ACT apricot

Service Manual305 pages