13-14 Remote Operations Models 2500 and 2502 User’s Manual
Program messages
A program message is made up of one or more command words sent by the computer to
the instrument. Each common command is a three letter acronym preceded by an asterisk
(*). SCPI commands are categorized in the :STATus subsystem and are used to explain
how command words are structured to formulate program messages.
:STATus Path (Root)
:OPERation Path
:ENABle <NRf> Command and parameter
:ENABle? Query command
:PRESet Command
Single command messages
The above command structure has three levels. The first level is made up of the root com-
mand (:STATus) and serves as a path. The second level is made up of another path
(:OPERation) and a command (:PRESet). The third path is made up of one command for
the :OPERation path. The three commands in this structure can be executed by sending
three separate program messages as follows:
:stat:oper:enab <NRf>
:stat:oper:enab?
:stat:pres
In each of the above program messages, the path pointer starts at the root command (:stat)
and moves down the command levels until the command is executed.
Multiple command messages
You can send multiple command messages in the same program message as long as they
are separated by semicolons (;). The following is an example showing two commands in
one program message:
:stat:oper; :stat:oper:enab <NRf>
When the above is sent, the first command word is recognized as the root command (:stat).
When the next colon is detected, the path pointer moves down to the next command level
and executes the command. When the path pointer sees the colon after the semicolon (;), it
resets back to the root level and starts over.
Commands that are on the same command level can be executed without having to retype
the entire command path. Example:
:stat:oper:enab <NRf>; enab?
After the first command (:enab) is executed, the path pointer is at the third command level
in the structure. Since :enab? is also on the third level, it can be typed in without repeating
the entire path name. Notice that the leading colon for :enab? is not included in the pro-
gram message. If a colon were included, the path pointer would reset to the root level and
expect a root command. Since :enab? is not a root command, an error would occur.
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