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Atari 400 Hardware Manual

Atari 400
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IRQEN
(IRQ
Interrupt
Enable)(D20E):
This
address
writes
data
to
the
IRQ
Interrupt
Enable
bits.
D7
D6
0
disable,
corresponding
IRQST
bit
is
set
to
1
1
enable
DS
D4
D3
D2
D1
DO
D7
Break
Key
Interrupt
Enable
D6
Other
Key
Interrupt
Enable
DS
Serial
Input
Data
Ready
Interrupt
Enable
D4
Serial
Output
Data
Needed
Interrupt
Enable
D3
Serial
Out
Transmission
Finished
Interrupt
D2
Timer
4
Interrupt
Enable
D1
Timer 2
Interrupt
Enable
DO
Timer
1
Interrupt
Enable
Enable
OS
SHADOW:
POKMSK
(hex
10)
Use AND's and OR's
to
change
one
bit
in
POKMSK
without
affecting
the
others.
Store
the
desired
value
in
both
IRQEN
and
POKMSK.
C.
TV
LINE
CONTROL
VCOUNT
(Vertical
Counter)(D40B):
This
address
reads
the
Vertical
TV
Line
Counter
(8 most
significant
bits).
D7
V8
D6
DS
D4
D3
V7
V6
vs
V4
D2
D1
V3
V2
DO
V1
VO
not
read.
VO
Two
line
resolution
supplied.
WSYNC
(Wait
for
Horizontal
Blank
Synchronism
-
i.e.
wait
until
start
of
next
TV
line.)(D40A):
not
used
This
address
sets
a
latch
that
pulls
down
on
the
RDY
line
to
the
microprocessor,
causing
it
to
wait
until
this
latch
is
automatically
reset
by
the
beginning
of
horizontal
blank.
Display
list
interrupts
may
be
delayed
by
1
line
if
WSYNC
is
used.
(Used by
OS
keyboard
click
routine.)
III.
3

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Atari 400 Specifications

General IconGeneral
ManufacturerAtari
Model400
TypeHome Computer
Release Year1979
CPUMOS Technology 6502
CPU Speed1.79 MHz
ROM10 KB
Operating SystemAtari OS
KeyboardMembrane keyboard
RAM8 KB (expandable to 48 KB)
GraphicsANTIC and GTIA chips
Sound4 channels
DisplayRF output for connection to TV
StorageOptional cassette tape drive or floppy disk drive
PortsCartridge
Display Resolution320x192 (16 colors)

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