National Instruments GPIB-PC - Manual (Page 98)

Section Four A BASICA/QuickBASIC GPIB-PC Function Calls
©National Instruments Corp. 4A-23 GPIB-PC User Manual
BASICA/QuickBASIC BASICA/QuickBASIC
IBCMDA IBCMDA
Purpose: Send commands asynchronously from string
Format: CALL IBCMDA (BD%,CMD$)
Remarks: BD% specifies an interface board. CMD$ contains the
commands to be sent over the GPIB.
The IBCMDA function is used to transmit interface
messages (commands) over the GPIB. These commands,
which are listed in Appendix A, include device talk and
listen addresses, secondary addresses, serial and parallel
poll configuration messages, and device clear and trigger
instructions. The
IBCMDA function is also used to pass
GPIB control to another device. This function is NOT used
to transmit programming instructions to devices.
Programming instructions and other device-dependent
information are transmitted with the write and read
functions.
IBCMDA is used in place of IBCMD when the application
program must perform other functions while processing the
GPIB I/O operation.
IBCMDA returns after starting the I/O
operation. If the number of bytes to send is small and the
bytes are accepted quickly by the GPIB device(s), the
operation may complete on the initial call. In this case,
the CMPL bit will be set in
IBSTA% . If the operation does
not complete on the initial call, you should monitor the
IBSTA% variable after subsequent calls (usually IBWAIT
calls) to know that the I/O is completed. When CMPL
becomes set in
IBSTA% , indicating that the I/O is
complete, the number of bytes sent is reported in the
IBCNT% variable.
Between the issuing of the IBCMDA call and the
corresponding CMPL, other GPIB function calls to this
board will return the error EOIP, with the following
exceptions:
• IBSTOP - to cancel the asynchronous I/O;
• IBWAIT - to monitor other GPIB conditions; and