ACT apricot - Page 19

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HARDWARE

Connections

for

the

printer, data

communications

equipment

and

mains

input

are located

at

the

rear of

the

System

Unit,

together

with

connectors

for

the

Keyboard

and

Display

Units.

The

expansion

slots

and

the

connection

for

the

light

pen

and

associated

circuitry

are located

within

the

System

Unit.

The

connection

for

the

"mouse"

device is

located

at

the

rear of

the

Keyboard

Unit.

SYSTEM

UNIT

All

the

processing

and

control

circuitry

within

the

System

Unit

is

contained

on

a single

printed

circuit

board,

designated

the

System

Board,

which

is 'fitted

horizontally

inside

the

System

Unit

housing.

The

major

elements

of

the

System

Board are

illustrated

on

the

block

diagram, Figure

2a/2b.

The

System

Board incorporates

the

following

items:

(a)

The

system

processing

elements.

(b)

The

Boot PROMs.

(c)

256 Kbytes of DRAM.

(d)

A floppy

disk

controller.

(e)

A parallel

printer

interface.

(f)

A

dual

channel

serial interface, one

channel

for

the

Keyboard

and

the

other

for

the

RS232C connector.

(g)

A display controller.

(h)

Two

expansion

slots.

The

processing

elements

on

the

System

Board are

arranged

in

a

multiprocessing

configuration

which

includes

two

Intel16-bit

microprocessors;

an

8086

central

processing

unit

(CPU)

and

an

8089

input/output

processor (lOP).

The

two

microprocessors are

connected

in

parallel

and

share a

common

bus

structure.

This

configuration is

termed

(by

Intel), a local

multiprocessing

configuration.

The

number

of

microprocessors

within

the

local

multiprocessing

configuration

is

increased

to

three

if

the

optional

lntel8087

numeric

data

processor (NDP) is fitted.

In

the

local

multiprocessing

configuration,

only

one

of

the

microprocessors

has

access

to

the

shared address,

control

and

data

buses

at

anyone

time.

The

input/output

processor is

employed

to

perform

the

bulk

of

routine

data

transfers,

under

the

direction

of

the

central

processing

unit.

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Service Manual305 pages