User 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 simply a three letter acronym preceded by an
asterisk (*). SCPI commands are categorized in the :STATus subsystem and are used to
help 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 (:OP-
ERation) 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 (;). Here 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 re-
type 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 program
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.
2000-900 (J - Aug 2010) BOOK.fm Page 36 Wednesday, October 12, 2011 12:29 PM