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8 root specifier, 9 message terminator, 5 understanding the command structure – KEPCO EL Series Electronic Load Operator Manual P/N 243-1295 Firmware Version 1.232 (Unit Rev 0 or 1) User Manual

Page 48: 6 program message syntax summary, Root specifier -14, Message terminator -14, Understanding the command structure -14, Program message syntax summary -14

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3-14

SERIES EL 063010

3.10.4.8 ROOT SPECIFIER

The root specifier is a colon (:) that precedes the first keyword of a program message. This
places the parser at the root (top left, Figure 3-4) of the command tree. Note the difference
between using the colon as a keyword separator and a root specifier in the following examples:

SYST:RANG:VOLT 100 Both colons are keyword separators.

:CURR:LEV:IMM 100 The first colon is the root specifier, the other two are keyword separators.

VOLT:LEV 60;:CURR:LEV 150 The second colon is the root specifier, the first and third are key-
word separators

:INP ON;:LOCK OFF;:CURR 120;VOLT:LEV 60 The first three colons are root specifiers.

3.10.4.9 MESSAGE TERMINATOR

The message terminator defines the end of a message. One message terminator is permitted:

• new line () is defined as CR (Carriage Return, 0D

H

) followed by LF (Line Feed, 0A

H

)

NOTE: The examples shown in this manual assume a message terminator will be added at the

end of each message. Where a message terminator is shown it is represented as
meaning CR (0D

H

) followed by LF (0A

H

).

3.10.5

UNDERSTANDING THE COMMAND STRUCTURE

Understanding the command structure requires an understanding of the subsystem command
tree illustrated in Figure 3-4. The “root” is located at the top left corner of the diagram. The
parser goes to the root if:

• a message terminator is recognized by the parser
• a root specifier is recognized by the parser

Optional keywords are enclosed in brackets [ ] for identification; optional keywords can be omit-
ted and the electronic load will respond as if they were included in the message. The root level
keyword [SOURce] is an optional keyword. Starting at the root, there are various branches or
paths corresponding to the subsystems. The root keywords for the EL Series

are :MEASure,

:INPut, :OUTPut, [:SOURce], :PROTection, :SENSe, :STATus, and :SYSTem. Because the
[SOURce] keyword is optional, the parser moves the path to the next level, so that VOLTage,
CURRent, and MEASure commands are at the root level.

Each time the parser encounters a keyword separator, the parser moves to the next indented
level of the tree diagram. As an example, the STATus branch is a root level branch that has
three sub-branches: OPERation, CHANnel, and QUEStionable.

3.10.6

PROGRAM MESSAGE SYNTAX SUMMARY

• Common commands begin with an asterisk (*).

• Queries end with a question mark (?).

• Program messages consist of a root keyword and, in some cases, one or more message

units separated by a colon (:) followed by a message terminator. Several message units