Technical data

Using the STATus System 27
Agilent N8201A Performance Downconverter Synthetic Instrument Module, 250 kHz to 26.5 GHz 543
• 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 not 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 do not want the added
complexity of setting up an SRQ handler
To monitor a condition:
1 Determine which register contains the bit that reports the condition.
2 Send the unique SCPI query that reads that register.
3 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.
Do this by querying the condition registers which continuously monitor status. These
registers represent the current state of the instrument. Bits in a condition register are
updated in real time. When the condition monitored by a particular bit becomes true, the
bit is set to 1. When the condition becomes false, the bit is reset to 0.
• Monitor a particular condition (bit).
You can enable a particular bit(s), using the event enable register. The instrument will then
monitor that particular condition(s). If the bit becomes true (0 to 1 transition) in the event
register, it will stay set until the event register is cleared. Querying the event register allows
you to detect that this condition occurred even if the condition no longer exists. The event
register can only be cleared by querying it or sending the *CLS command.
• Monitor a particular type of change in a condition (bit).