Remote Interface Reference 3
E364xA User’s and Service Guide 139
To read the Status Byte summary register, send the IEEE-488 serial poll message.
Querying the summary register will return a decimal value which corresponds to
the binary-weighted sum of the bits set in the register. Serial poll will
automatically clear the request service bit in the Status Byte summary register. No
other bits are affected. Performing a serial poll will not affect instrument
throughput.
Using *STB? to read the status byte
The *STB? (Status Byte query) command is similar to a serial poll but it is
processed like any other instrument command. The *STB? command returns the
same result as a serial poll but the “request service” bit (bit 6) is not cleared.
The *STB? command is not handled automatically by the IEEE-488 bus interface
hardware and will be executed only after previous commands have completed.
Polling is not possible using the *STB? command. Executing the *STB? command
does not clear the Status Byte summary register.
Using the Message Available bit (MAV)
You can use the Status Byte “Message Available” bit (bit 4) to determine when
data is available to read into your bus controller. The power supply subsequently
clears bit 4 only after all messages have been read from the output buffer.
The IEEE-488 standard does not ensure synchronization between your bus
controller program and the instrument. Use the
*OPC?
command to
guarantee that commands previously sent to the instrument have
completed. Executing a serial poll before a
*RST
,
*CLS
, or other commands
have completed can cause previous conditions to be reported.
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