IBRDA
Board-Level/Device-Level
Purpose
Read data asynchronously from a device into a user buffer.
Format
C
| unsigned long ibrda (int ud, void *rdbuf, size_t count) |
Visual Basic
| CALL ibrda (ud%, rdbuf$) |
or
| status% = ilrda (ud%, rdbuf$, count&) |
Interactive Control (Usage Notes)
ibrda count
Input
| ud | Board or device unit descriptor |
| count | Number of bytes to be read from the GPIB |
Output
| rdbuf | Address of buffer into which data is read |
| Function Return | The value of Ibsta |
Description
Device-Level
If ud is a device descriptor, ibrda addresses the GPIB, begins an asynchronous read of up to count bytes of data from a GPIB device, and places the data into the buffer specified by rdbuf. The operation terminates normally when count bytes have been received or END is received. The actual number of bytes transferred is returned in the global function Ibcnt.
Board-Level
If ud is a board descriptor, ibrda reads up to count bytes of data from a GPIB device and places the data into the buffer specified by rdbuf. A board-level ibrda assumes that the GPIB is already properly addressed. The operation terminates normally when count bytes have been received or END is received. The operation terminates with an error if the board is not the CIC, and the CIC sends a Device Clear on the GPIB. The actual number of bytes transferred is returned in the global function Ibcnt.
Board- and Device-Level
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 has begun, 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
| EABO | Board-level: a Device Clear message was received from the CIC. |
| EADR | Board-level: The GPIB is not correctly addressed; use ibcmd to address the GPIB. |
| Device-level: A conflict exists between the device GPIB address and the GPIB address of the device access board. Use ibconfig, options IbcPAD and IbcSAD. | |
| EARG | Either the buffer or the count is invalid. |
| EBUS | Device-level: No devices are connected to the GPIB. |
| ECIC | Device-level: The access board is not CIC. See Device-Level Calls and Bus Management. |
| 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. |
| EOIP | Asynchronous I/O is in progress. |