Remote Interface Reference 4
Keysight 34420A User’s Guide 181
– Use a serial poll to check to see when bit 5 (standard event) is set in the status
byte summary register. You could also configure the meter for an SRQ
interrupt by sending *SRE 32 (status byte enable register, bit 5).
How to Use the Message Available Bit (MAV)
You can use the status byte “message available” bit (bit 4) to determine when data
becomes available to read into your bus controller. The meter sets bit 4 when the
first reading trigger occurs (which can be TRIGger:SOURce:IMMediate). The
meter subsequently clears bit 4 only after all messages have been read from the
output buffer.
The message available (MAV) bit can only indicate when the first reading is
available following a READ? command. This can be helpful if you do not know
when a trigger event such as BUS or EXTernal will occur.
The MAV bit is set only after all specified measurements have completed when
using the INITiate command followed by FETCh?. Readings are placed in the
meter’s internal memory when using INITiate. Sending the FETCh? command
transfers readings (stored in internal memory by the INITiate command) to the
meter’s output buffer. Therefore, the MAV bit can only be set after all
measurements have been completed.
Using *OPC to Signal When Data is in the Output Buffer
Generally, it is best to use the “operation complete” bit (bit 0) in the standard
event register to signal when a command sequence is completed. This bit is set in
the register after an *OPC command has been executed. If you send *OPC after a
command which loads a message in the meter’s output buffer (either reading data
or query data), you can use the operation complete bit to determine when the
message is available. However, if too many messages are generated before the
*OPC command executes (sequentially), the output buffer will fill and the meter
will stop taking readings.
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