Instrument messages

In contrary to interface messages such as "LAN interface messages" or "GPIB interface messages", instrument messages are employed in the same way for all interfaces.

There are different types of instrument messages, depending on the direction they are sent:

  • Commands

  • Instrument responses

The structure and syntax of the instrument messages are described in "SCPI command structure".

Commands

Commands (program messages) are messages that the controller sends to the instrument. They operate the instrument functions and request information. The commands are subdivided according to two criteria:

  • According to the effect on the instrument:

    • Setting commands cause instrument settings such as a reset of the instrument or setting the frequency.

    • Queries cause data to be provided for remote control, for example, for identification of the instrument or polling a parameter value. Queries are formed by appending a question mark directly to the command header.

  • According to the definition of commands in standards:

    • Common commands: Their function and syntax are precisely defined in standard IEEE 488.2. They are employed identically on all instruments (if implemented). They are used for functions such as managing the standardized status registers, resetting the instrument, and performing a self-test.

    • Instrument control commands depend on the features of the instrument, such as frequency settings. Many of these commands have also been standardized by the SCPI committee.

      In some manuals, these commands are marked as "SCPI compliant" in the command reference chapters. Commands without this SCPI label are instrument-specific. However, their syntax follows SCPI rules as permitted by the standard.

Instrument responses

Instrument responses (response messages and service requests) are messages that the instrument sends to the controller after a query. Responses can contain measurement results, instrument settings and information on the instrument status.