Atari 400 Service Manual

the different output devices, such as PIA chip, POKEY chip and the
CTIA chip.
Only four of the possible output selections are used. ( See Table 4-
3. ) The I/O Decoder is enabled by inputs on pins 4, 5, and 6; pin 4
input coming from the Memory Map Decoder (S6); pin 5 input coming the
Address Bus and pin 6 input coming from the Chip Select (CS) line.
The Binary Decode is provided by the Address Bus (A08, A09 and A10).
Table 4-3. I/O Decoder Select Lines
Enable/Pin Binary Decode
A
1
2
6
A
1
1
5
S
6
4
A
1
0
3
A
9
2
A
8
1
Active
Pin
Device
Selected
H L L L L L Y0 - 15 CTIA
H L L L L H Y1 - 14 Not Used
H L L L H L Y2 - 13 POKEY
H L L L H H Y3 - 12 PIA
H L L H L L Y4 - 11 Not Used
H L L H L H Y5 - 10 External
Select
Y6 - 9 Not Used
Y7 - 8 Not Used
ATARI Personal Computers 4-13
4.3.3 Motherboard Console System (800)

Atari 400 Specifications

General

Manufacturer	Atari
Model	400
Type	Home Computer
Release Year	1979
CPU	MOS Technology 6502
CPU Speed	1.79 MHz
ROM	10 KB
Operating System	Atari OS
Keyboard	Membrane keyboard
RAM	8 KB (expandable to 48 KB)
Graphics	ANTIC and GTIA chips
Sound	4 channels
Display	RF output for connection to TV
Storage	Optional cassette tape drive or floppy disk drive
Ports	Cartridge
Display Resolution	320x192 (16 colors)