10 Introduction To Programming
Types of SCPI Messages
There are two types of SCPI messages, program and response.
• A program message consists of one or more properly formatted SCPI commands sent from the controller to
the power module. The message, which may be sent at any time, requests the power module to perform some
action.
• A response message consists of data in a specific SCPI format sent from the power module to the controller.
The power module sends the message only when commanded by a special program message called a "query."
Types of SCPI Commands
SCPI has two types of commands, common and subsystem. Common commands generally are not related to specific
operation but to controlling overall power module functions, such as reset, status, and synchronization. All common
commands consist of a three-letter mnemonic preceded by an asterisk:
*RST *IDN? *SRE 8
Subsystem commands perform specific power module functions. They are organized into an inverted tree structure with the
"root" at the top (see Figure 3-2). Some are single commands while others are grouped within specific subsystems.
Note If you have the optional Agilent 66001A MPS Keyboard, you may want to use it as a quick introduction
to message structure. See "Appendix A".
Structure of a SCPI Message
SCPI messages consist of one or more message units ending in a message terminator. The terminator is not part of the
syntax, but implicit in the way your programming language indicates the end of a line (such as a newline or end-of-line
character).
The Message Unit
The simplest SCPI command is a single message unit consisting of a command header (or keyword) followed by a message
terminator.
ABOR<newline>
VOLT?<newline>
The message unit may include a parameter after the header. The parameter usually is numeric, but it can be a string:
VOLT 20<newline>
VOLT MAX<newline>
Combining Message Units
The following command message is briefly described here, with details in subsequent paragraphs.