Specifications

Operating Manual SEFRAM 4451
M4451 A00
37
4.9.1 General Command Structure
The device commands are generally defined by the SCPI standard, with the exception of those
instrument functions for which SCPI commands do not as yet exist.
The Common Commands and Queries are defined by IEEE 488.2. The command syntax, i.e.
how a command is structured, is defined by IEEE 488.2.
4.9.2 The Program Message
A Program Message is defined as a string containing one or more Program Message Units, each
of which is an instrument command or query. Program Message Units are separated from each
other by the Program Message Unit Separator. The Program Message is terminated by the
Program Message Terminator.
The Program Message Unit Separator consists of a semicolon (';'), optionally preceded and/or
followed by white-space characters. A white-space character is defined as the ASCII characters
in the ranges 00H-09H, and 0BH-20H. This range includes the ASCII control characters and the
space, but excludes the Linefeed character.
The Program Message Terminator consists of optional white-space characters, followed by one
of three options:
 Linefeed (LF) character (ASCII 0A);
 GPIB EOI bus line being set true on the last byte of the message;
 LF being sent with EOI true.
The Program Message Unit can be divided into three sections as follows.
4.9.2.1 Program Message Header
The Program Header represents the operation to be performed, and consists of ASCII character
mnemonics. Two types of Program Headers are used in the SEFRAM 4451: Instrument-control
headers and Common Command and Query headers. A Program Header may consist of more
than one mnemonic, in which case the mnemonics are separated from each other by the colon
(':'). For instrument control commands, the mnemonics are specified by the SCPI standard, and
indicate the tree structure of the command set. The first mnemonic indicates the subsystem
being controlled. Common Command and Query Program Headers consist of a single
mnemonic prefixed by an asterisk ('*').
The mnemonics consist of upper- or lower-case alpha characters. Mnemonics may be written in
either the long form, in which the entire mnemonic is written out, or the short form, in which
only a specified portion of the mnemonic is written out. Some mnemonics have only one form
due to their short length. Where a command is described, the portion appearing in upper case is
the short form. Only the short form or the long form may be used.
Example: The command to set the period to 1 microsecond may be written in the following
ways:
SOURCE:PULSE:PERIOD 1US
SOUR:PULS:PER 1US
SOURCE:PULSE:PERIOD 1US
Some mnemonics in a specified Program Header may be optional. This is indicated in the
command description by the mnemonic being enclosed in square brackets ([...]).
This means it is not necessary to write the mnemonic into the Program Header: it is a default
condition. The 'SOURCE' mnemonic, for example, is optional. Not specifying it will cause the
device to search for the mnemonics in the Program Header under the Source Subsystem. For
example, the period may be set by the command:
:PULS:PER 1US
4.9.2.2 Program Message Header Separator
The Program Header Separator is used to separate the program header from the program data. It
consists of one or more white-space characters, denoted as <ws>. Typically, it is a space.
4.9.2.3 Program Message Data