Atari 400 Technical Reference Manual page 59

GET CHARACTERS and GET RECORD
The Handler returns data in the following format:
7 0
+-+-+-+-+-+-+-+-+
data byte
+-+-+-+-+-+-+-+-+
PUT CHARACTERS and PUT RECORD
The
Handl~r
accepts data in the following format:
7 0
+-+-+-+-+-+-+-+-+
data byte
+-+-+-+-+-+-+-+-+
The Handler attaches no significance to the data bytes
written, a value of $98 (EOL) causes no special action.
GET STATUS
'The Handler does no
more
than set the status to $01.
Theory of Operation
The Cassette Handler writes and reads all data in fixed-length records
of the format shown below:
Figure 5-9
74
+-+-+-+-+-+-+-+-+
:01010 10 1:
+-+-+-+-+-+-+-+-+
:0 1 0 1 0 1 0 1:
+-+-+-+-+-+-+-+-+
t control byte
+-+-+-+-+-+-+-+-+
128
= data
=
bytes
+-+-+-+-+-+-+-+-+
checksum
+-+-+-+-+-+-+-+-+
Speed measurement bytes.
(Managed by SIO, not the
Hand ler. )
Cassette Handler Record Format
OPERATING SYSTEM C016555 -- Section 5