Atari 400 Hardware Manual

HITCLR (Collision "HIT" Clear)
DOlE
This write address clears all collision bits described
above.
F. AUDIO
Not
Used
AUDCTL (Audio Control)(D208): This address writes data into the Audio
Mode Control Register. (Also see SKCTL two-tone bit 3 and notes).
I D7 : D6 : D5
D4 D3 D2 Dl
DJ
D7 Change 17 bit poly into a 9 bit below poly.
D6 Clock Channel 1 with 1.?9 MHZ, instead of 64KHZ.
D5 Clock Channel 3 with 1.79 MHZ, instead of 64KHZ.
D4 Clock Channel 2 with Channel 1, instead of 64KHZ (16 BIT).
D3 Clock Channel 4 with Channel 3, instead of 64KHZ (16 BIT).
D2 Insert Hi Pass Filter in Cha~nel 1, clocked by Channel 3.
(See section II.)
Dl Insert Hi Pass Filter in Channal 2, clocked by Channel 4.
DO Change Normal 64 KHZ frequency, into 15 KHZ.
Exact Frequencies: The frequencies given above are approximate. The
Exact Frequency (fin) that clocks the divide by N counters is given below
(NTSC only, PAL different).
FIN FIN
Exact)
1.79 MHZ 1.78979 MHZ
Use modified formula for fout
64 KHZ 63.9210 KHZ
Use normal formula for fout
15 KHZ
15.6999 KHZ
The Normal Formula for output frequency is:
Fout Fin/2N
Where N =The binary number in the frequency register (AUDF), plus 1 (N=AUDF+1).
The MODIFIED FORMULA should be used when Fin= 1.79 MHZ and a more exact result
is desired:
Where:
M
M
Fout Fin
2(AUDF + M)
4 if 8 bit counter (AUDCTL bit 3 or 4 = 0)
7
if 16 bit counter (AUDCTL bit 3 or 4 = 1)
III .12

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)