Measurement Computing GPIB-488 - Manual (Page 19)

Chapter 3 GPIB 488.1 Library Reference
Programming Reference Manual 3-6 GPIB-488
IBCAC
Makes the specified board the Active Controller.
Syntax
C ibcac (int board, int sync)
Parameters
board is an integer containing the board handle
sync specifies if the GPIB board is to take control synchronously or asynchronously. If sync
is 0, the GPIB board takes control asynchronously. Otherwise, it takes control synchronously
(immediately).
When the board takes control, the GPIB interface board asserts the ATN line. When taking
control synchronously, the board waits for any data transfer to be completed and then takes
control. Note that if synchronous take control is specified while an
ibrd or ibwrt operation
is in progress, the synchronous take control may not occur if a timeout or other error occurs
during the
ibrd / ibwrt .
In comparison, if the board is to take control asynchronously, it takes control immediately,
without waiting for any data transfers to be completed.
Returns
ibsta will contain a 16-bit status word as described in Appendix B, IBSTA .
iberr will contain an error code, if an error occurred. In particular, the ECIC error occurs if
the specified GPIB board cannot become an Active Controller.
Usage Notes
This routine is only used when doing board level I/O.
Example
GPIB board 1 takes control asynchronously.
C ibcac (brd1, 0);