Megatel Quark/100 Specifications download pdf (Page 14)

The

QUARK

Video

Display Interfaces

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

The

on-card Video Display

Interface

is

an

integral

part

of

the

Megatel

QUARK~

It

is

capable of operating in

either

Alphanumeric

or Graphics

modes.

TTL-driven

video, horizontal

sync,

and

vertical

sync

signals are provided for connection to

direct-drive

CRT

data displays.

Additionally,

a composite video output

at

approximately

1V

p

_

p

is

provided

for

use with

monochrome

displays with composite video inputs.

The

data displayed

on

the

CRT

are stored in a

segment

of the

Main

Memory

of the

QUARK.

The

meory

bank

in

which

the

Video

Display

Memory

is located

is

determined

by

bit

0 of the

CPU's

I-register.

In

Alphanumeric

mode,

a

total

of

32

character

rows

are

scanned

for

each

video

frame

on

the

60Hz

version

(assuming

a

60Hz

frame

rate)

and

40

rows

on

the

50Hz

version

(assuming

a

50Hz

frame rate)_

However,

not

all

of the

scanned

rows

may

be

displayed.

The

first

row,

which

represents data within the

first

half-page of the

Video

Display

Memory,

is

displayed during the

Vertical Retrace Period.

There

being

no

hardware

mechanism

to

bLank

the video output during

the VerticaL Retrace period,

this

part of the

Video

Display

Memory

must

be

loaded

with data

that will generate a

nuLL

video output.

The

simplest

manner

in

which

to

do

this

is

to load

00

bytes into that part of the

Video

Display

Memory

which

is

scanned

during the retrace period.

The

Bootstrap

PROM

routine loads a

'bLank"

character into the Character Generator for the

00

character

code,

so

that

when

a

row

of

00

bytes

is

displayed,

no

video output

will

result.

The

second

line

of

the

display

can

be

used

for

display

purposes

if

the

CRT

monitor

employed

terminates the Vertical Retrace Interval

sufficiently

quickly.

On

many

monitors,

however,

characters

displayed

in

this

row

will

appear

slanted

because

of

the

monitor's

inability

to

recover

from

the Vertical Retrace Interval

in

time

to

properly display the

first

severaL scan lines.

Thus

the video driver routines included with standard

QUARK

operating

systems

do

not

use

the

second

displayable

row

on

the video display.

The

QUARK

is

equipped with a

Programmable

Character Generator. This allows the

eight-bit

by

eight-bit

patterns for the characters displayed

on

the

CRT

to

be

loaded

or altered under

software control.

Custom

character sets

may

be designed,

saved

on

floppy disk,

and

loaded

when

needed.

This si

mpL

ifies

the task of accomodating

appL

i cation programs requi ring

Languages

other

than

English,

or

running programs using

special

symbols,

or

of using programming

languages

which

employ

special character

sets

(e.g.

the

APL

programming

language).

Whi

le

normaLly

an

entire

character set

<256

characters)

would

be

loaded

as

one

step

(as

is

done

by

the

uti

l

ity

programCHRLD.COM)

character patterns

can

be

loaded

or

modified

on

a byte-by-byte

basis,

so

it

is

not

necessary to

load

an

entire

set of characters. This

may

permit special

video

effects

in

some

applications.

The

Programmable

Character Generator

used

on

the

QUARK

is

a 2048-byte

static

memory

which

is independent of the

Main

Memory.

A

uti

L

ity

routine to

load

the

Programmable

Character

Generator with a standard character set

as

the operating system

is

booted

is

included with the

QUARK

operating system software.

ALso

incLuded

is

a character set

editor

utiLity,

which

can

be

used to customize the standard character set or to create

new

character

sets.

These

user-

defined character

sets

can

be

saved

on

a

fLoppy

diskette.

The

Bit-mapped Graphics

Mode

of the

Monochrome

Video

Display Interface

aLLows

graphic data

to

be displayed

on

the

CRT.

In

this

mode,

individuaL

bits

in the

Video

Display

Memory

are

mapped

onto single dots

(pi

xeLs)

on

the

CRT.

For

60Hz

models,

24k

of

Main

Memory

is

used

to

display (typically)

143,360

pixels, organized.

as

640

horizontaLly

by

224

vertically.

On

50Hz

models,

30k

is

used

to display (typically) 179,200

pixels,

organized

as

640

by

280

pixels.

Megatel

Computer

Technologies Toronto,

Canada

Page

H/W-9'"

1 2 ... 9 10 11 12 13 14 15 16 17 18 19 ... 85 86

Comments to this Manuals

No comments