List of
Contents
Page
INTRODUCTION ..... ..... .... .... ....... ................................. 1
DESCRIPTION .... ........... .............. ...... ............ ........ ........ 3
General ............................................................................ 3
Printer Interface .............................................................. 4
System Control Interface ............................................... 6
List of
Illustrations
Figure
Parallel
Interface
block
diagram
..................................... 1
Centronics
Connector
pin
detail
.................................... 2
INTRODUCTION
The
Parallel
Interface
is
located
on
the
System
Board
and
consists
of
the
elements
of
circuitry
as
detailed
on
the
block
diagram
Figure
1.
The
interface
performs
the
following
functions
within
the
equipment:
(a)
Provides
the
communications
interface
between
the
equipment
and
an
external
printer,
via
the
Centronics
connector.
(b)
Allows
the
processors
to
detect
the
active
display
period
on
the
screen
of
the
Display
Unit,
by
utilising
a
control
output
from
the
CRT
control
circuitry.
(c)
Produces
a series of
control
outputs
to
various
areas
. of
circuitry,
under
software
control.
The
control
outputs
are
as follows:
(a)
Two
control
outputs
to
determine
the
selection
of
floppy
disk
drive.
(b)
An
output
to
control
the
Read/Write
head
loading of
the
floppy
disk
drives.
(c)
A
control
output
to
switch
the
Display
Unit
on
and
off.
(d)
A
control
output
to
select
graphics
or
alphanumeric
mode.
(e)
A
control
output
to
reset
the
CRT
control
circuits.
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