IBCMDA
Board-Level
Purpose
Send GPIB commands asynchronously.
Format
C
| unsigned long ibcmda (int ud, const void *cmdbuf, size_t count) |
Visual Basic
| CALL ibcmda (ud%, cmdbuf$) |
or
| status% = ilcmda (ud%, cmdbuf$, count&) |
Interactive Control (Usage Notes)
ibcmda cmdbuf
Input
| ud | A board unit descriptor |
| cmdbuf | Buffer of command bytes to send |
| count | Number of command bytes to send |
Output
| Function Return | The value of Ibsta |
Description
ibcmda sends count bytes from cmdbuf over the GPIB as command bytes (interface messages). The number of command bytes transferred is returned in the global function, Ibcnt. Refer to the list of IEEE 488 command messages for defined interface messages.
Command bytes are used to configure the state of the GPIB. They are not used to send instructions to GPIB devices. Use ibwrt to send device-specific instructions.
The asynchronous I/O calls (ibcmda, ibrda, ibwrta ) are designed so that applications can perform other non-GPIB operations while the I/O is in progress. Once the asynchronous I/O begins, further NI-488.2 calls are strictly limited. Any calls that would interfere with the I/O in progress are not allowed; the driver returns EOIP in this case.
Once the I/O is complete, the application must resynchronize with the NI-488.2 driver. Resynchronization is accomplished by using one of the following calls:
| ibwait | If the returned Ibsta contains CMPL, the driver and application are resynchronized. |
| ibnotify | If the Ibsta value passed to the ibnotify callback contains CMPL, the driver and application are resynchronized. |
| ibstop | The I/O is canceled; the driver and application are resynchronized. |
| ibonl | The I/O is canceled and the interface is reset; the driver and application are resynchronized. |
Possible Errors
| ECIC | The interface is not Controller-In-Charge. |
| EDVR | The NI-488.2 driver is either configured incorrectly or is not properly installed. |
| EHDL | ud is invalid or out of range. |
| ELCK | The requested operation could not be performed because of an existing lock by another process. |
| ENEB | The interface is not installed or is not properly configured. |
| ENOL | No Listeners are on the GPIB. |
| EOIP | Asynchronous I/O is in progress. |