1. Short and long forms
According to SCPI each command header can have short and long form. In order to distinguish both forms in command syntax description, upper and lower case characters are used. Note, that SCPI is case-insensitive, the usage of upper and lower case characters is done solely for the purpose of syntax definition. You may even mix upper and lower case. There is no semantic difference between upper and lower case in program messages. Same applies for parameters – they may have short and long forms.
Example 1. Let’s consider such syntax description: SYSTem:CONFigure <parameters>
Here SYST and CONF specify the short form, and SYSTem and CONFigure specify the long form. It means that the instrument will accept the following command headers: syst:conf , SYST:CONF , SYSTEM:CONFIGURE, SYST:CONFIGURE, or even sYstEm:cOnFiGuRE. However, SYSTE or CONFIG headers are not allowed and will cause a command error, because they don’t refer to short or long forms.
Example 2. Let’s consider such syntax description :FORMat[:DATA] <format> , where <format> is one of ASCii, REAL or PACKed. Such argument syntax indicates that the argument may be specified as: ASCII, ASC, asc, REAL, real, PACKED, pack, PACK.
2. Default nodes and arguments
SCPI standard states that some nodes in SCPI commands tree may play role of default nodes. That means that it is not required to specify them in command headers. Same applies for arguments. In this manual optional nodes and arguments are denoted with square brackets.
For example, let’s consider the following syntax description: :FETCh[:SCALar]? [<series name>]
Here square brackets indicate the fact that the node inside them (SCALAR) is default node under its parent node (FETCH). That means that you can specify the header as: :FETCH or :FETCH:SCALAR and result will be same. Same applies for parameters in square brackets. In this syntax <series name> parameter is marked as optional. Exact behavior of a command with omitted parameter is specified separately for each command.