Megatel Quark/100 Specifications download pdf (Page 20)

-----------------,------

Peripheral Interfaces

-------,

The

Megatel

QUARK

provides a

number

of

parallel

and

serial

1/0

lines.

While

some

of these

lines are intended for

use

with specific peripherals,

such

as

parallel-

or

serial-interface

printers,

many

of these

1/0

lines

may

be

used

for

more

general purposes

if

the intended devices

are not being

used

in a

particular

application. A discussion of these

1/0

ports follows. In

addition, specialized peripheral subsystems,

such

as

the Floppy-disk Controller provide a high

level of

1/0

support.

------------------------

Parallel

Printer

Interface

-_.

_

..

---------------

The

QUARK

includes a port intended for the connection of

an

eight-bit

parallel-interface

printer.

This port consists of

an

eight-bit

latch for the output data, a

Data

Strobe output

line,

and

an

Acknowledge

input line. All of the input

and

output lines for

this

port are

TTL-

compatible.

Eight-bit

parallel

data is written to the port

by

an

output instruction

to

1/0

address

5Fhex.

The

data appearing

on

the output pins of the

QUARK

(see Table I for the pinout of the

connector) represent the true

state

of the data written to the port.

The

Data

Strobe line for the port is controlled

by

the

CA2

control line of the

VIA.

The

CA2

control line

must

be configured

as

an

output in the Peripheral Control Register

(PCR)

of

the

VIA,

by

setting

bits

2

and

3 of the

PCR.

The

CA2

output drives a

TTL

inverter, the output

of

which

is connected to the

Data

Strobe output pin (pin

C-13).

Thus

the logic

state

of the

actual

Data

Strobe output

is

the inverse of the

state

of the

CA2

line,

as determined

by

bit

1

of the

PCR.

This

TTL

inverter is capable of sinking

24mA.

The

Acknowledge

input for the Parallel Printer Port

is

directly

connected

to

the

CA1

input

line of the

VIA.

The

active

transition

of the

CA1

input of

this

line

wi

II

set

a flag in the

Interrupt

Flag

Register

(IFR)

of

the

VIA.

The

setting

of

this

flag

may

also

generate

an

interrupt

if

the appropriate

bit

in the Interrupt

Enable

Register

CIER)

of the

VIA

is

set.

This interrupt

can

be

used

to interrupt the

CPU

when

the

printer

is

ready

to

accept another

character,

depending

on

the operation of the printer.

Handshaking

using the

Data

Strobe

and

Acknowledge

lines

is

not

automatic, that

is

that the

routine

handl

ing

the

Parallel

Printer Interface

must

write the output latch, toggle the

Data

Strobe line

in

the

manner

required for the interface of the

printer,

and

then act accordingly

for the

printer's

response

on

the

Acknowledge

input.

If

it

is

not

desired

to

use

this

port with a

parallel

printer,

then the eight

Data

lines,

the

Acknowledge Input

line,

and

the

inverted

output

line

from

CA2

may

be used

for

other

purposes

such

as

might

be required for a

particular

application of the

QUARK.

--,------,

Parallel

Keyboard

Interface

-------------

The

QUARK

provides

an

interface for

an

ASCII-encoded

parallel-output

keyboard. This

interface uses the Port A

1/0 lines

and

the

CA2

control line of the

PIA.

As

initial

ized

by

standard

CP/M

operating systems provided

on

the Distribution Diskettes, active-high

ASCII

data

present

on

the

PAD-7

lines of the

PIA

will

be

read

after

a negative-going stobe pulse

on

CA2.

Note

that the data present

on

the input lines is

not

actually latched into the Input

Data

register

when

the strobe occurs,

so

the

keyboard

data

must

remain

valid

between

the strobe

and

the read.

(This

is

not

usua

lly

a problem.)

If

it

is

not intended

to

use

an

encoded keyboard

for

a

particular

application

of

the

QUARK,

then

these

eight

1/0

lines

and

the

CA2

control

line

may

be

used

for

any

other

1/0

functions

which

might

be

required.

It

is

possible, for instance,

to

connect

an

un-encoded

Megatel

Computer

Technologies Toronto,

Canada

Page

H/W-15

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