Keithley 2520, Service Manual, Page: 130 / 137

B-10 Calibration Reference Model 2520 Pulsed Laser Diode Test System Service Manual
Status byte EAV (Error Available) bit
Whenever an error is available in the error queue, the EAV (Error Available) bit (bit 2) of
the status byte will be set. Use the *STB? query to obtain the status byte, then test bit 2 to
see if it is set. If the EAV bit is set, an error has occurred, and you can use the appropriate
error query to read the error and at the same time clear the EAV bit in the status byte.
Generating an SRQ on error
To program the instrument to generate an IEEE-488 bus SRQ (Service Request) when an
error occurs, send the following command: *SRE 4. This command will enable SRQ when
the EAV bit is set. You can then read the status byte and error queue as outlined above to
check for errors and to determine the exact nature of the error.
Detecting calibration step completion
When sending remote calibration commands, you must wait until the instrument com-
pletes the current operation before sending another command. You can use either *OPC?
or *OPC to help determine when each calibration step is completed.
Using the *OPC? query
With the *OPC? (operation complete) query, the instrument will place an ASCII 1 in the
output queue when it has completed each step. To determine when the OPC response is
ready, do the following:
1. Repeatedly test the MAV (Message Available) bit (bit 4) in the status byte and wait
until it is set. (You can request the status byte by using the *STB? query.)
2. When MAV is set, a message is available in the output queue, and you can read the
output queue and test for an ASCII 1.
3. After reading the output queue, repeatedly test MAV again until it clears. At this
point, the calibration step is completed.