944-959



     the recorder or disk. LIST (except to the display screen), LOAD
     and LPRINT also close all sound voices. The RUN from tape or
     disk and SAVE commands use channel seven, as does LIST.
     The bytes within each IOCB are used as follows:

     Label     Offset  Bytes Description
     --------------------------------------------------------------------
     ICHID     0       1     Index into the device name
     table for the currently OPEN file. Set by the OS. If not in use, the
     value is 255 ($FF), which is also the initialization value.
     
     ICDNO     1       1     Device number such as one
     for Dl: or two for D2:. Set by the OS.

     ICCOM     2       1     Command for the type of
     action to be taken by the device, set by the user. This is the first
     variable after the channel number in an OPEN command. See
     below for a command summary. Also called ICCMD.

     ICSTA     3       1     The most recent status
     returned by the device, set by the OS. May or may not be the
     same value as that which is returned by the STATUS request in
     BASIC. See the OS User's Manual, pp. 165-166, fora list of status
     byte values.

     ICBAL/H   4,5     2     Two-byte (LSB,MSB) buffer
     address for data transfer or the address of the file name for OPEN,
     STATUS, etc.

     ICPTL/H   6,7     2     Address of the device's put-
     one-byte routine minus one. Set by the OS at OPEN command,
     but not actually used by the OS (it is used by BASIC, however).
     Points to CIO's "IOCB NOT OPEN" message at powerup.

     ICBLL/H   8,9     2     Buffer length set to the
     maximum number of bytes to transfer in PUT and GET
     operations. Decremented by one for each byte transferred;
     updated after each READ or WRITE operation. Records the
     number of bytes actually transferred in and out of the buffer after
     each operation.

     ICAX1     10      1     Auxiliary byte number one,
     referred to as AUX1. Used in the OPEN statement to specify the
     type of file access: four for READ, eight for WRITE, twelve for
     both (UPDATE). Not all devices can use both kinds of operations.
     This byte can be used in user-written drivers for other purposes
     and can be altered in certain cases once the IOCB has been
     OPENed (see the program example above). For the S: device, if
     AUX1 equals 32, it means inhibit the screen clear function when
     changing GRAPHICS modes. Bit use is as follows for most
     applications: