All commands, unless specifically noted in the commands syntax descriptions, have a query form. Exceptions are noted as:

As defined in IEEE-488.2, a query is a command with a question mark symbol appended (examples are *ESR? and *TST?). When a query form of a command is received, the current setting associated with the command is placed in the output buffer. Query commands always return the short form of the parameter. For example, NORMal or INVerted is returned as NORM or INV. Boolean values are returned as 1 or 0, even when they can be set as ON or OFF.

Typical SCPI commands consist of one or more keywords, parameters, and punctuation. SCPI command keywords can be a mixture of upper and lower case characters. Except for common commands, each keyword has a long and a short form. In this manual, the long form is presented with the short form in upper case and the remainder in lower case. For example, the long form of the command keyword to control the instrument display is :DISPlay.

The short form keyword is usually the first four characters of the long form (example: DISP for DISPlay). The exception to this is when the long form is longer than four characters and the fourth character is a vowel. In such cases, the vowel is dropped and the short form becomes the first three characters of the long form. Example: the short form of the keyword :POWer is :POW.

Some command keywords may have a numeric suffix to differentiate between multiple instrument features such as multiple pulse widths. For example, keywords :WIDTh2 (or :WIDT2).

As with any programming language, the exact command keywords and command syntax must be used. The syntax of the individual commands is described in detail in SCPI Commands. Unrecognized versions of long form or short form commands, or improper syntax, will generate an error.

All SCPI commands, except the common commands, are organized in a hierarchical structure similar to the inverted tree file structure used in most computers. The SCPI standard refers to this structure as “the Command Tree.” The command keywords that correspond to the major instrument control functions are located at the top of the command tree. The command keywords for the MS4640A SCPI command set are shown in the diagram below.

All MS4640A SCPI commands have one or more subcommands (keywords) associated with them to further define the instrument function to be controlled. The subcommand keywords may also have one or more associated subcommands (keywords). Each subcommand level adds another layer to the command tree. The command keyword and its associated subcommand keywords form a portion of the command tree called a command subsystem. The :FORMat command subsystem is shown below.

Data parameters, referred to simply as “parameters,” are the quantitative values used as arguments for the command keywords. The parameter type associated with a particular SCPI command is determined by the type of information required to control the particular instrument function. For example, Boolean (ON | OFF) type parameters are used with commands that control switch functions.

The command descriptions in SCPI Commands specify the type of data parameter to be used with each command. The most commonly used parameter types are numeric, extended numeric, discrete, and Boolean.