Program Messages - Keithley 2001 Operator's Manual

IEEE-488 Reference
4.9.2

Program messages

4-34
The complete short-form version of the above command is as follows:
:stat:oper?
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 into subsystems and are structured as command paths. The
following command paths are contained in the :STATus subsystem and are used to help explain
how command words are structured to formulate program messages.
:STATus
:OPERation
:PTRansition <NRf>
:NTRansition <NRf>
:ENABle <NRf>
:PRESet
1. Single command messages: There are three levels to the above command structure. The first
level is made up of the root command (: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 three
commands for the :OPERation path. The four commands in this structure can be executed by
sending four separate program messages as follows:
:stat:oper:ptr <NRf>
:stat:oper:ntr <NRf>
:stat:oper:enab <NRf>
: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.
2. Multiple command messages: Multiple commands can be sent in the same program message
as long as they are separated by semicolons (;). Example showing two commands in one pro-
gram message:
:stat:pres; :stat:oper:enab
When the above message 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 re-
sets 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
After the first command (:enab) is executed, the path point is at the third command level in the
structure. Since :ptr and :ntr are also on the third level, they can be typed in without repeating
the entire path name. Notice that the leading colon for :ptr and :ntr are 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 neither :ptr nor :ntr are root commands, an error would occur.
3. Command path rules:
Path (Root)
Path
Command and parameter
Command and parameter
Command and parameter
Command
<NRf>
<NRf>; ptr <NRf>; ntr <NRf>
2001-900-01 Rev. J / October 2009