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2 - Introduction to Programming
22
Header
Convention
In the command descriptions in Chapter 3 of this manual, headers are emphasized with
boldface type. The proper short form is shown in upper-case letters, such as DELay.
Header
Separator
If a command has more than one header, you must separate them with a colon
(VOLT:PROT OUTPut:RELay:POLarity).
Optional
Headers
The use of some headers is optional. Optional headers are shown in brackets, such as
OUTPut[:STATe] ON. As previously explained under "The Effect of Optional Headers", if
you combine two or more message units into a compound message, you may need to
enter the optional header.
Query Indicator
Following a header with a question mark turns it into a query (VOLTage?, VOLTage:PROTection?). If a
query contains a parameter, place the query indicator at the end of the last header
(VOLTage:PROTection? MAX).
Message Unit Separator
When two or more message units are combined into a compound message, separate the units with a
semicolon (STATus:OPERation?;QUEStionable?).
Root Specifier
When it precedes the first header of a message unit, the colon becomes the root specifier. It tells the
command parser that this is the root or the top node of the command tree. Note the difference between
root specifiers and header separators in the following examples:
OUTPut:PROTection:DELay .1
All colons are header separators
:OUTPut:PROTection:DELay .1
Only the first colon is a root specifier
OUTPut:PROTection:DELay .1;:VOLTage 12.5
Only the third colon is a root specifier
NOTE: You do not have to precede root-level commands with a colon; there is an implied colon in
front of every root-level command.
Message Terminator
A terminator informs SCPI that it has reached the end of a message. Three permitted messages
terminators are:
u newline (<NL>), which is ASCII decimal 10 or hex 0A.
u end or identify (<END>)
u both of the above (<NL><END>).
In the examples of this guide, there is an assumed message terminator at the end of each message. If the
terminator needs to be shown, it is indicated as <NL> regardless of the actual terminator character.