Agilent Technologies 34420A, User Manual

Page: 165 / 294

Using
*STB?
to Read the Status Byte
The
*STB?
(status byte query) command is similar to a serial poll except
it is processed like any other instrument command. The
*STB?
command
returns the same result as an
IEEE-488
serial poll except that the
“request service” bit (bit 6) is not cleared if a serial poll has occurred.
The
*STB?
command is not handled automatically by the
IEEE-488
bus
interface hardware and the command will be executed only after previous
commands have completed. Polling is not possible using the
*STB?
command. Using the
*STB?
command does not clear the status byte
summary register.
To Interrupt Your Bus Controller Using
SRQ
•
Send a bus device clear message.
•
Clear the event registers with the
*CLS
(clear status) command.
•
Set the
*ESE
(standard event register) and
*SRE
(status byte register)
enable masks.
•
Send the
*OPC?
(operation complete query) command and enter the
result to assure synchronization.
•
Enable your bus controller’s
IEEE-488 SRQ
interrupt.
To Determine When a Command Sequence is Completed
Either:
•
Send the
*OPC?
(operation complete query) command and enter the
result to assure synchronization.
Or, to prevent holding the interface bus for commands that take longer
to execute (such as CALibrate commands), :
•
Send a device clear message to clear the meter’s output buffer.
•
Clear the event registers with the
*CLS
(clear status) command.
•
Enable “operation complete” using the
*ESE 1
command (standard
event register).
•
Send your programming command string, and place the
*OPC
(operation complete) command as the last command.
•
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).
4
Chapter 4 Remote Interface Reference
The SCPI Status Model
163