Atari 800XL Service Manual

SYSTEM INTERFACE
The
800XL
provides
the
following
interfaces:
*
Serial
input/output
(SIO)
*
Controller
Jacks
*
Parallel
Bus Interface
(PBI)
*
Cartridge
Interface
*
Keyboard
Interface
SERIAL INPUT/OUTPUT (SIQ) INTERFACE
The
Atari
800XL
communicates
with
peripheral
devices via
an
asynchronous
serial
port
(
1 9.2K
Baud rate
max.),
Data is
transmitted
and
received
as eight
bits
of serial
data.
LSB is sent first
precede
d
by a logic
zero start
bit
and
succeeded
by a
logic
one stop
bit
The serial
data out
is
transmitted
or
received
as positive
logic.
The
serial
data
out line
always
assumes its new
state
when
the
serial
clock
out
line
goes high.
Clock
out goes low
in
the center
of data
ait.
The
bus
protocol
specifies
that
all
commands
must
originate
from
the computer
and
that
peripherals
present
data
on the
bus only
when
commanded
to
do so. Every
bus operation
goes to
completion
before
another
bus
operation
is
initiated.
An
error
detected
k
any
point in the
bus
operation
aborts
the
entire
sequence. A
bus
operation
consists
of
the
following
elements:
-
Command
Frame
(From
Computer)
-
Command
Frame
1)
Data
Send
2)
Date
Receive
3)
Immediate
(No
Data-Command
Only,
i.e.,
status)
-
Acknowledge
Frame
( From
Peripheral)
-
Optional
Data
Frame
(To
Or
From
Computer)
-
Complete
Frame
(From Peripheral)
18

Atari 800XL Specifications

General

Manufacturer	Atari
Type	Home computer
Release year	1983
CPU	MOS Technology 6502C
RAM	64 KB
ROM	24 KB
Operating System	Atari OS
CPU Speed	1.79 MHz (NTSC) / 1.77 MHz (PAL)
Graphics	ANTIC and GTIA chips
Display resolution	160×192 to 320×192 pixels
Sound	POKEY chip
Storage	Cassette tape, floppy disk
Ports	Serial, parallel, monitor, joystick ports