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3.6.4
PROGRAM MESSAGE STRUCTURE
SCPI program messages (commands from controller to power supply) consist of one or more
message units ending in a message terminator. The message terminator is not part of the syntax; it
is defined by the way your programming language indicates the end of a line ("newline" charac-
ter). Sending a character with EOL line asserted is another way of sending a message termina-
tor. The message unit is a keyword consisting of a single command or query word followed by a
message terminator (e.g., CURR?<newline> or TRIG<end-of-line>). The message unit may
include a data parameter after the keyword separated by a space; the parameter is usually
numeric (e.g., CURR 5<newline>), but may also be a string (e.g., OUTP ON<newline>). Figure
3-19 illustrates the message structure, showing how message units are combined. The follow-
ing subparagraphs explain each component of the message structure.
NOTE: An alternative to using the message structure for multiple messages defined in the fol-
lowing paragraphs is to send each command as a separate line. In this case each com-
mand must use the full syntax shown in Appendix B.
3.6.4.1
KEYWORD
Keywords are instructions recognized by a decoder within the BOP, referred to as a "parser."
Each keyword describes a command function; all keywords used by the BOP are listed in Figure
3-18.
Each keyword has a long form and a short form. For the long form the word is spelled out com-
pletely (e.g. STATUS, OUTPUT, VOLTAGE, and TRIGGER are long form keywords). For the
short form only the first three or four letters of the long form are used (e.g., STAT, VOLT, OUTP,
and TRIG). The rules governing short form keywords are presented in Table 3-21.
TABLE 3-21. RULES GOVERNING SHORTFORM KEYWORDS
IF NUMBER OF LETTERS IN
LONGFORM KEYWORD IS:
4 OR FEWER
5 OR MORE
You must use the rules above when using keywords. Using an arbitrary short form such as
ENABL for ENAB (ENABLE) or IMME for IMM (IMMEDIATE) will result in an error. Regardless
of which form chosen, you must include all the letters required by that form.
To identify the short form and long form in this manual, keywords are written in upper case let-
ters to represent the short form, followed by lower case letters indicating the long form (e.g.,
IMMediate, EVENt, and OUTPut). The parser, however, is not sensitive to case (e.g., outp,
OutP, OUTPUt, ouTPut, or OUTp are all valid).
3.6.4.2
KEYWORD SEPARATOR
If a command has two or more keywords, adjacent keywords must be separated by a colon (:)
which acts as the keyword separator (e.g., CURR:LEV:TRIG). The colon can also act as a root
specifier (paragraph 3.6.4.7).
BOP HIPWR 080709
AND FOURTH LETTER
IS A VOWEL?
(DOES NOT MATTER)
NO
YES
THEN SHORT FORM
CONSISTS OF:
ALL LONG FORM LETTERS
THE FIRST FOUR
LONG FORM LETTERS
THE FIRST THREE
LONG FORM LETTERS
EXAMPLES
MODE
MEASure, OUTPut, EVENt
LEVel, IMMediate, ERRor
3-57
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