KEPCO TMA VXI-27 - Manual (Page 30)

TMA VXI -27 101602
3-13
3.5.4.8 MESSAGE TERMINATOR
The message terminator defines the end of a message. Three message terminators are permit-
ted:
• new line (<NL>), ASCII 10 (decimal) or 0A (hex)
• (<CR>), ASCII 13 (decimal) or 0D (hex)
• both of the above (<CR> <NL>)
Your GPIB interface card software will automatically send a message terminator. For example,
the HP BASIC OUTPUT statement inserts <NL> after the last data byte. When binary data is
exchanged, <END> must be used. The combination <NL><END> terminator can be used for all
data except binary data.
NOTE: Kepco power modules require a message terminator at the end of each program mes-
sage. 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 <NL> regardless of the actual terminator character.
3.5.5 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 power supply 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 TMA VXI-27 are :INITiate,
:MEASure, :OUTPut, [:SOURce], :STATus, and :SYSTem. Because the [SOURce] keyword is
optional, the parser moves the path to the next level, so that VOLTage, CURRent, and FUNC-
tion 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, PRESet, and QUEStionable. The following illustrates how
SCPI code is interpreted by the parser:
STAT:PRES<NL>
The parser returns to the root due to the message terminator.
STAT:OPER?;PRES<NL>
The parser moves one level in from STAT. The next command is expected at the level defined
by the colon in front of OPER?. Thus you can combine the following message units
STAT:OPER? and STAT:PRES;
STAT:OPER:COND?;ENAB 16<NL>
After the OPER:COND? message unit, the parser moves in one level from OPER, allowing the
abbreviated notation for STAT:OPER:ENAB.