Vector 4 - Page 19

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VECTOR

GRAPHIC,

INC.

RAM/PROM

MEMORY

(Cont.)

RAM-

Sixteen

4164s

(128

K

system),

four

74LS189s

and

one

T4LS670.

The

4164

Dynamic

RAM

is

used

for

numerous

functions.

These

include

holding

the

system

CP/M,

Video

Memory,

User

Memory

and

booting

routines.

The

memory

map

can

be

configured

to

accomodate

the

graphies

and

color

mode.

Refresh

is

accomplished

as

a

result

of

the

video

access

rate.

|

RAM-

An

additional

RAM

memory

board

(using

sixteen

more

4164s)

can

be

added

to

increase

main

memory

from

128

K

to

256

K.

The

T7T4LS189s

are

used

to

map

the

upper,

Z80B,

"local"

address

lines

A11-Al5

to

the

upper,

"Global"

address

lines

A11-A17.

This

allows

the

Z80B

to

use

the

complete

256

K

bloeck

of

internal

memory

(In

32

K

increments).

The

8088-2

can

directly

use

the

"global"

address

range

00000H

to

3FFFFH.

The

first

4

K

bloek

of

Dynamic

RAM

address

space

is

disabled

to

allow

the

Executive

program

to

access

the

2732

(or

2764)

PROM

during

Reset

or

Power-On

sequences.

The

T4LS670

is

used

to

map

video

data

(coming

from

Dynamic

RAM)

with

other

signals

so

the

320

Graphic

Modes

(320h

by

312v

pixels)

can

be

implemented.

|

1/Q

Serial

Ports-

Three

8251

USART

Chips

are

used

to

interface

with

the

keyboard,

serial

printer

and

modem.

Keyboard

00H

(Data)

01H

(Status/Control)

Modem

04H

(Data)

05H

(Status/Control)

Serial

Printer

06H

(Data)

07H

(Status/Control)

Parallel

Ports-

One

8255

programmable

I/O

chip

(with

supplementary

decoder

chips)

is

used

to

interface

with

parallel

printers

using

either

a

"Centronies

or

Qume

type"

protocol.

Port

A

08H

Port

B

09H

Port

C

0AH

Control

Register

Port

0BH

I

1-2

7200-0001

09-01-82