National Instruments NI-488.2 - page 80

Chapter 8 NI-488.2 Programming Techniques
NI-488.2 User Manual 8-8 ni.com
// If the ERR bit is set in LocalIbsta, then print an error
// message and return.
if (LocalIbsta & ERR) {
printf ("GPIB error %d has occurred. No more callbacks.\n",
LocalIberr);
DeviceError = TRUE;
return 0;
}
// Read the serial poll byte from the device. If the ERR bit is set
// in ibsta, then print an error message and return.
LocalIbsta = ibrsp (LocalUd, &SpollByte);
if (LocalIbsta & ERR) {
printf ("ibrsp failed. No more callbacks.\n");
DeviceError = TRUE;
return 0;
}
// If the returned status byte equals the expected response, then
// the device has valid data to send; otherwise it has a fault
// condition to report.
if (SpollByte != expectedResponse) {
printf("Device returned invalid response. Status byte = 0x%x\n",
SpollByte);
DeviceError = TRUE;
return 0;
}
// Read the data from the device. If the ERR bit is set in ibsta,
// then print an error message and return.
LocalIbsta = ibrd (LocalUd, ReadBuffer, 40L);
if (LocalIbsta & ERR) {
printf ("ibrd failed. No more callbacks.\n");
DeviceError = TRUE;
return 0;
}
// The string returned by ibrd is a binary string whose length is
// specified by the byte count in ibcntl. However, many GPIB
// instruments return ASCII data strings and this example makes this
// assumption. Because of this, it is possible to add a NULL
// character to the end of the data received and use the printf()
// function to display the ASCII data. The following code
// illustrates that.
ReadBuffer[ibcntl] = ‘\0’;