Programming Fundamentals 5
N9310A User’s Guide 97
Program and Response Messages
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 signal generator accepts either
:RFOutput:STATE ON or :RFOutput:STATe 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
:RFOutput:STATe?), the response is always 1, regardless of
if you previously sent
:RFOutput:STATe 1 or
:RFOutput:STATE ON.
1 represents logic state 1 = ON; logic state 0 = OFF
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