Program And Response Messages - Keysight N9320B Programmer's Manual

Programming Fundamentals

Program and Response Messages

Program and Response Messages
20
To understand how your instrument and controller communicate
using SCPI, you must understand the concepts of program and
response messages.
Program Messages
Program messages are the formatted data sent from the controller
to the instrument. Conversely, response messages are formatted
data sent from the instrument to the controller. Program messages
contain one or more commands, and response messages contain
one or more responses.
Response Messages
The controller may send commands at any time, but the instrument
sends responses only when query commands is received. All query
mnemonics end with a question mark. Queries return either
measured values or internal instrument settings.
Forgiving Listening and Precise Talking
SCPI uses the concept of forgiving listening and precise talking
outlined in IEEE 488.2.
Forgiving listening means that instruments are very flexible in
accepting various command and parameter formats. For example,
the spectrum analyzer accepts either
:FREQuency:CENTer:STEP:AUTO ON
:FREQuency:CENTer:STEP:AUTO 1
Precise talking means that the response format for a particular
query is always the same. For example, if you query RF output state
when it is on (using
:FREQuency:CENTer:STEP:AUTO
the response is always 1, regardless of if you previously sent
:FREQuency:CENTer:STEP:AUTO ON
:FREQuency:CENTer:STEP:AUTO 1.
or
),
?
or