User`s guide

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Vector

ZCB

Single

Board Oomputer

except

for

110

baud,

are

obtained

by

successively

dividing

this

frequency

in

half

using

Ul,

which

is

74LS393

binary

counters.

The

clock

frequency

for

llO

baud

is

generated

by

dividing

the

frequency

for

1200

baud

by

11.

The

desired

frequency

is

selected

by

a DIP

switch

for

each

serial

port,

and

applied

to

the

TxC

am

RxC

pins

of

the

8251.

The

8251

USARl'

is

design~

to

interface

easily

to

an

8080

bus

structure,

am

the

control

signals

RD/, C/D,

CS/,

and

WR/

are

derived

easily

from

the

ZCB

internal

control

bus.

Since

the

device

was

intended

to

be

used

with

a

bi-directional

data

bus,

EIA

RS-232C

line

drivers

and

receivers

interface

the

RxD

and

TxD

OJtput

of

the

8251

to

the

OJtside

world.

Rev.

I-B

6/11/80

3-3