Atari 400 Technical Reference Manual page 220

G7 ICPTL,ICPTH [0346,2] -- PUT BYTE vector
See Section 5. Initialized to point to CIO's "IOCB not OPEN" routine
at power-up and system reset.
G8 ICBLL,ICBLH [0348,2] -- Buffer length / byte count
See Section
5.
G9 ICAX1,ICAX2 [034A,2] -- Auxiliary information
See Section
5.
Gi0 ICSPR [034C,4J -- Spare bytes Tor Handler use
There is no fixed assignment of these four bytes; the Handler
associated with
~n
IOCB can or may not use these bytes.
Device status
Gil
DVSTAT [02EA,4] -- Device status
See Section 5 for a discussion of the GET STATUS command.
Device Table
G12 HATABS [031A,38] -- Device table
See Section 9 for a description of the device table.
CIC/Handler Interface Parameters
Communication between CIa and a Handler is accomplished using the
6502 machine regis~ers, and a data structure called the Zero-page
IOCB (ZIOCB). The ZIOCB is essentially
a
copy of the particular
IOCB being used for the current operation.
OPERATING SYSTEM C016555 -- Appendix L
235