How To Use The Status Registers - Keysight x-series User Reference Manual

3 Programming the Analyzer
STATus Subsystem
• *OPC, *OPC? (operation complete) sets the standard event status register to monitor the completion of
all commands. The query stops any new commands from being processed until the current processing is
complete, then returns a '1'.
• *PSC, *PSC? (power-on state clear) sets the power-on state so that it clears the service request enable
register and the event status enable register at power on.
• *SRE, *SRE? (service request enable) sets and queries the value of the service request enable register.
• *STB? (status byte) queries the value of the status byte register without erasing its contents.

How to Use the Status Registers

A program often needs to be able to detect and manage error conditions or changes in instrument status.
There are two methods you can use to programmatically access the information in status registers:
• The polling method
• The service request (SRQ) method
In the polling method, the instrument has a passive role. It only tells the controller that conditions have
changed when the controller asks the right question. In the SRQ method, the instrument takes a more
active role. It tells the controller when there has been a condition change without the controller asking.
Either method allows you to monitor one or more conditions.
The polling method works well if you do not need to know about changes the moment they occur. The SRQ
method should be used if you must know immediately when a condition changes. To detect a change using
the polling method, the program must repeatedly read the registers.
Use the SRQ method when:
• you need time-critical notification of changes
• you are monitoring more than one device which supports SRQs
• you need to have the controller do something else while waiting
• you can't afford the performance penalty inherent to polling
Use polling when:
• your programming language/development environment does not support SRQ interrupts
• you want to write a simple, single-purpose program and don't want the added complexity of setting up
an SRQ handler
• To monitor a condition:
a.Determine which register contains the bit that reports the condition.
b.Send the unique SCPI query that reads that register.
c.Examine the bit to see if the condition has changed.
You can monitor conditions in different ways.
• Check the current instrument hardware and firmware status.
102 EMI Receiver Mode Reference