Atari 400 Technical Reference Manual page 180

STORAGE FORMAT:
Tapes are recorded in
1/4
track stereo format at 1 7/8 inches per
second. The tape can be recorded in both directions, where tracks
1 and 2 are side A left and right; and tracks 3 and 4 are side B
r i gh t and
I
eft (i ndustry standard>. On each
5
ide, the left
channel
(1
or
4)
is used for audio and the right channel (2 and
3) is used for digital information.
The audio channel is recorded the normal way. The digital channel
is recorded using the POKEY two-tone mode producing FSK data at
up to 600 baud. The MARK frequency is 5327 Hz and the SPACE
frequency is
3995 Hz.
The transmission of data is asynchronous
byte serial as seen from the computer; POKEY reads or writes a
bit serial FSK sequence for each byte, in the following order:
1 start bit (SPACE)
data bit 0
-+
data bit 1
+-
0
=
SPACE, 1
=
MARK.
data bit 6
data bit
7
-+
1 stop bit (MARK)
The only control the computer has over tape motion is motor
start/stop; and this only if the PLAY button is pressed by the
user. In order for recording to take place, the user must press
both the REC and PLAY buttons on the cassette. The computer has
no way to sense the position of these buttons, nor even if an
ATARI 410 Program Recorder is cabled to the computer, so the user must
be careful when using this device.
SID INTERFACE
The cassette device utilizes portions of the serial bus hardware,
but does not follow any of the protocol as defined in Section 9.
ATARI 820[TM] 40-COLUMN IMPACT PRINTER
The ATARI
820
Printer has the following characteristics:
DATA CAPACITY:
40 characters per line (normal printing)
29
characters per line (sideways printing)
DATA TRANSFER RATES:
OPERATING SYSTEM C016555 -- Appendix K
195