Atari 400 Hardware Manual

H. SERIAL PORT (see peripheral connector on console)
SKCTL (Serial Port control)(D20F): This address writes data into the
register that controls the configuation of the serial port, and also the
Fast Pot Scan and Keyboard Enable.
D7 D6
D7
D6)
DS
D4
D3
D2
D1
DO
D5 D4 D3 D2 D1 DO
(Bits are normally zero
and perform the functions
shown below when true.)
Force Break (force serial output to zero (space))*
Serial Port Mode Control (see mode chart at end of
Serial port description, page II.34) .
Two Tone (Serial output transmitted as two tone signal instead of
logic true/false.)
Fast Pot (Fast Pot Scan. The Pot Scan Counter completes its
sequence in two TV line times instead of one frame time. The
capacitor dump transistors are completely disabled.)
Enable Key Scan (Enables Keyboard Scanning circuit)
Enable Debounce (Enables Keyboard Debounce circuits)
DO-D1 (Both Zero) Initialize (State used for testing and initializing
chip) **
OS SHADOW: SSKCTL (hex 232)
The
OS enables key scan and debounce and may change the other bits for
different I/O operations. In particular, an aborted cassette operation may
leave the two tone bit in the true state, causing undesirable audi o signals.
This may be corrected by writing hex 13 to both SKCTL and SSKCTL after doing
I/O and/or before modifying the audio registers.
* NOTE:
**NOTE:
When powered on, serial port ou tput may stay low even if this bit
is cleared. To get S.P. high (mark), send a byte out (recommend
00 or FF).
There is no original power on state. Pokey has no reset pin.
III .17

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)