HP 53181A Programming Manual page 68

Programming Your Counter for Remote Operation
Elements of SCPI Commands
Optional Keyword
Optional keywords are those which appear in square brackets ([ ]) in the command
syntax. (Note that the brackets are not part of the command and are not sent to the
Counter.)
Suppose you send a second level keyword without the preceding optional keyword.
In this case, the Counter assumes you intend to use the optional keyword and
responds as if you had sent it.
Examine the portion of the [:SENSe] subsystem shown below:
[:SENSe]
:FREQuency
:ARM
:STOP
:SOURce EXTernal
The root-level keyword [:SENSe] is an optional keyword. To set the Counter's
frequency stop arm to external, you can use either of the following:
:SENS:FREQ:ARM:STOP:SOUR EXT
or
:FREQ:ARM:STOP:SOUR EXT
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