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Triggering Measurements
Measurement Pacing
Measurement pacing can be accomplished by using the IEEE 488.2-1987
Common Commands *OPC, *OPC?, and *WAI. These commands are
implemented within the Test Set using the criteria that an operation has not
completed until
• all active measurements have obtained at least one valid measurement result
• all signals generated by the Test Set are within specifications.
Refer to the “Common Command Descriptions” on page 245 and the
IEEE 488.2-1987 Standard for more information on using these commands.
Arming Hardware-Triggered Measurements
Some measurements, such as the Tone Sequence Decoder, require an external
signal to trigger the measurement. These measurements require that the
measurement be “armed” in order for it to be triggered by the external signal. The
:TRIGger:IMMediate command is used to arm these types of measurements
within the Test Set.
When the trigger mode is set to RETRigger SINGle, the measurement must be
re-armed after each measurement cycle.
When the trigger mode is set to RETRigger REPetitive, the measurement is
continually re-armed after each measurement cycle.
NOTE: Bus Lock Up: If the required triggering signal is not received, or if the signal level
is incorrect, the measurement will not trigger and the measurement cycle will not
complete. If a measurement cycle does not successfully obtain a valid
measurement result, it will continue to try until it does (an external trigger is
detected) or until the measurement trigger is aborted. This is true for both
retriggering modes. This has the consequence that both the GPIB bus and the
Active Controller handshake are in a temporary holdoff state while the Active
Controller waits to read the measurement result from the Test Set.
The control program should include measurement time-out routines that CLEAR
the bus and ABORt the trigger if a measurement does not complete within a
specified amount of time. This provides a method of preventing the bus from
remaining in the temporary holdoff state indefinitely.