Megatel Quark/100 Specifications download pdf (Page 19)

The

example

and

description

above

assumed

that the interrupts

were

disabled throughout the

procedure.

would

also

possible to re-enable interrupts

after

loading the

Video

Memory

starting

address

and

changing

the polarity of the

CA1

active transition.

The

next negative

transition

of the

signal

would

generate

interrupt, immediately following

which

the

Graphics

mode

bit

and

the

bit

would

changed,

just

in the non-interrupt procedure

above.

return

Alphnumeric

mode,

is necessary only to set the Graphics/Alphanumeric

mode

bit,

and

then clear the

bit

in the

SAM,

and

set

the F-bits for the desired

Video

Display

Memory

location.

The

routine

below

set up the

Alphanumeric

mode

with the

Video

Display

Memory

located between

F000

and

FFFF,

as is set up

the Bootstrap

PROM.

;alpha-entry

example

routine

SAMV2C

EQU

0FF84H

iADDRESS

CLEAR

BIT

SAM

SAMF0C

EQU

0FF86H

;ADDRESS

CLEAR

BIT

SAM

SAMF1C

EQU

0FF88H

;ADDRESS

CLEAR

BIT

SAM

SAMF2S

EQU

0FF8BH

;ADDRESS

SET

BIT

SAM

SAMF3S

EQU

0FF8DH

;ADDRESS

SET

BIT

SAM

SAMFSS

EQU

0FF91H

;ADDRESS

SET

BIT

SAM

SAMF6S

EQU

0FF93H

;ADDRESS

SET

BIT

SAM

PIAPA

EQU

074H

PIACRA

EQU

07SH

PIAPB

EQU

076H

SAMSET

EQU

0000BH

ALPHA:

iTO

AVOID

GLITCHING

SCREEN,

THIS

POINT

SHOULD

SYNCHRONIZED

WITH

iVERTICAL

SYNC

SIGNAL

(SEE

GRAPHICS-ENTRY

EXAMPLE)

;DISABLE

INTERRUPTS

PIAPB

iREAD

CONTENTS

PIA

PORT

OUTPUT

ORI

40H

;SET

BIT

FOR

ALPHANUMERIC

MODE

OUT

PIAPB

LXI

H,SAMV2C

CALL

SAMSET

LXI

H,SAMF0C

CALL

SAMSET

LXI

H,SAMF1C

CALL

SAMSET

LXI

H,SAMF2S

CALL

SAMSET

LXI

H,SAMF3S

CALL

SAMSET

LXI

H,SAMFSS

CALL

SAMSET

LXI

H,SAMF6S

CALL

SAMSET

RET

This completes the routine to switch

from

graphics

mode

to alphanumeric

mode.

the

Programmable

Character Generator

the

QUARK

the patterns for the characters displayed

the

Alphanumeric

Mode

are

loaded

into

the

Character Generator under

software

control.

Once

loaded

the

contents

the

Character Generator

remain

unti l another character set

loaded

or unti C

power

to the

board

removed.

The

standard set

uti l

ity

routines included with the Distribution Software include

programs for loading the

Programmable

Character Generator

and

for designing character patterns

be loaded.

therefore

not

necessary to understand

how

the

Programmable

Character

Generator operates in order to

able to

make

use

this

feature.

Megatel

Computer

Technologies Toronto,

Canada

Page

H/W-14

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Megatel Quark/100 Specifications Page 19

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