SYSTEM BOARD
8086.
The
8086 processor is directly language-compatible
with
the
8088 processor
which
is
used
on
many
3rd
Generation
machines.
It
runs
at
a clock speed of 5 MHz,
typically
executing
1.4
million
instructions
per second,
and
has a 16-bit data-bus
which
enables
it
to
read and
write
words
into
memory
in
one
access as opposed to
two
with
the
8088.
8089.
The
8089
is
an
I/O
processor
and
two-channel
DMA
device
which
is
used
mainly
for disk reads and writes.
It
has
the
capability
to
transfer data from
memory
to memory,
memory
to
port,
port
to
memory
and
port
to port
8087
(optional).
The
8087
mathematics
co-processor is used
in
parallel
with
the
8086. Full floating-point and
intrinsic
arithmetic
is supported and
the
8087
has
its
own
instruction
set
which
in
effect extends
the
instruction
set
of
the
8086.
Communications
Handling
The
Apricot
has
two
peripheral ports, a parallel
printer
port driven by
the
Intel
8255 PIO,
and
a serial
communications
port
driven by
the
Zilog Z80 SIO.
Z80
SIO.
The
Z80
Serial
I/O
Controller
has
two
independant
full-duplex
channels
with
separate control and
status
lines for
modems
or
other
devices.
Data
rates from a
to
SOaK
bits/second
can
be accomplished. Full Synchronous
and
Asynchronous
control is provided,
but
the
current
BIOS
only supports
Asynchronous
protocols. In
the
Async mode,
5,6,
7 or 8
bits/character
and variable stop-bit configuration
is available. Also
included
is Break
Generation
and
detection,
parity,
overrun
and
framing error detection.
The
controller itself also
has
interfacing for daisy-chain
interrupt
vectoring
without
external logic.
8255A-5
PI~.
The
8255 Parallel
Input/Output
interface
provides
the
communications
interface
between
the
Apricot
and
an
external
printer, via
the
Centronics
connector.
It
also produces a series of control
outputs
to
various areas of
circuitry
under
software control.
Though
bi -directional
communication
is supported
in
hardware,
the
current
BIOS
only
uses
the
standard
form of
communication.
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