Chapter 4 Remote Interface Reference
The SCPI Status Registers
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Caution 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.
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.
To Interrupt Your Bus Controller Using SRQ
1 Send a device clear message to clear the power supply's output buffer (e.g., CLEAR
705).
2 Clear the event registers with the *CLS (clear status) command.
3 Set up the enable register masks. Execute the *ESE command to set up the Standard
Event register and the *SRE command for the Status Byte.
4 Send the *OPC? (operation complete query) command and enter the result to ensure
synchronization.
5 Enable your bus controller's IEEE-488 SRQ interrupt.
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