Atari 800XL Field Service Manual

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MEMORY
(ROMS AND DRAMS)
O.S. ROM
The SOOXL
operating system
is
resident in one
I6K X 8
ROM, The
ROM address
inputs are
from CPU
address
lines AO through
A! 3- The chip
selects from
the
address
decoding circuitry and
generates data on CPU
data lines
DO through D7*
The
ROM
requires a
power
input ol
+5 volts.
BASIC ROM
The
Atari 800XL has built-in Atari
BASIC (Rev. B) residing
in an 8K X 8
ROM-
Thli
Is
equivalent
to having an
Atari BASIC cartridge
permanentJy
plugged into
the
console. Any cartridge plugged into the
computer,
takes precedence
over the
buUl-ln
BASIC
DRAMS
The SOOXL Dynamic Random Access
Memories
(DRAMS) consist of
eight
6*fK X 1
DRAMS.
MEMORY
MANAGEMENT UNIT (MMU)
The memory
management unit
(MMU)
address decoding
circuitry
consists
of
a
PLA
(Programmable Logic Array )
LC,
one
3 to
8 decoder
and a
few
gates-
The
input
to the
circuitry
Includes the ad*ess
lines
A8
through A13 as
well as
control
signals, such
as ROM enable (from
PIA) and
DRAM
refresh
from
ANTIC-
Some
of
the
most
imporUnt outputs of
this circuitry
include
select
signals for
the
GT1A»
POKEY, PIA,
OS ROM, DRAMS,
BASIC and
cartridge-
800XL Computer
Field Service
Manual
1-9

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