Remote Control
R&S
®
FPC
192
User Manual 1178.4130.02 ─ 07
command recognition and execution. The receipt of DCL clears the input buffer and
immediately resets the command recognition.
19.1.3.2
Command Recognition
Here the expression "instrument hardware" denotes the part of the instrument fulfilling
the actual instrument function - signal generation, measurement etc. The controller is
not included. The term "data base" denotes a database that manages all the parame-
ters and associated settings required for setting the instrument hardware.
Setting commands lead to an alteration in the data set. The data set management
enters the new values (for example frequency) into the data set, however, only passes
them on to the hardware when requested by the command recognition. This only takes
place at the end of a program message.
The data are checked for compatibility with the current instrument settings before they
are transmitted to the instrument hardware. If the execution is not possible, an "execu-
tion error" is signaled to the status reporting system. The corresponding settings are
discarded.
Before passing on the data to the hardware, the settling bit in the
STATus:OPERation
register is set (refer to
STATus:OPERation
register). The hardware executes the set-
tings and resets the bit again as soon as the new state has settled. This fact can be
used to synchronize command servicing.
Queries induce the data set management to send the desired data to the output unit.
19.1.3.3
Output Unit
The output unit collects the information requested by the controller, which it receives
from the data base management. It processes it according to the SCPI rules and
makes it available in the output buffer.
If the instrument is addressed as a talker without the output buffer containing data or
awaiting data from the data base management, the output unit sends error message
Query UNTERMINATED
to the status reporting system. No data are sent to the control-
ler, the controller waits until it has reached its time limit. This behavior is defined by
IEEE
488.2 and SCPI.
19.1.4
SCPI Command Structure
SCPI commands consist of a header and, in most cases, one or more parameters. The
header and the parameters are separated by a "white space" (ASCII code 0 to 9, 11 to
32 decimal, e.g. blank). The headers may consist of several mnemonics (keywords).
Queries are formed by appending a question mark directly to the header.
The commands can be either device-specific or device-independent (common com-
mands). Common and device-specific commands differ in their syntax.
Remote Control Basics
