Fluke NORMA 4000 Operators, User Manual, Page: 23 / 184

Remote Control Basics
Instrument Model and Command Processing
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Syntactic errors in commands are detected here and transferred to the status reporting
system. The rest of a command line following a syntax error is further analyzed and
processed as far as possible.
If the command recognition recognizes a terminator or a DCL (GPIB only) command, it
requests the data set to set the commands now also in the instrument hardware. After this,
it is immediately ready to continue processing commands. This means that new
commands can be processed while the hardware is being set ("overlapping execution").
Currently all commands sent to the instrument are executed non overlapped (=sequential).
Data Set and Instrument Hardware
The term "instrument hardware" is used here to designate the part of the instrument that
actually performs the instrument functions: signal generation, measurement, etc. The
controller is not included.
The data set is a detailed reproduction of the instrument hardware in the software.
Interface setting commands cause an alteration of the data set. The data set management
enters the new values (for example, frequency) into the data set but passes them on to the
hardware only upon request by the command recognition. As this is only effected at the
end of a command line, the sequence of setting commands in the command line is not
relevant.
The data are only checked for compatibility among one another and with the instrument
hardware immediately before they are transferred to the instrument hardware. If it is
found that an execution is not possible, an “execution error” is signalled to the status
reporting system. All alterations made to the data set are cancelled, and the instrument
hardware is not reset. Due to the delayed checking and hardware setting, it is permissible
that impermissible instrument states are briefly set within a command line without an
error message being produced. At the end of the command line, however, a permissible
instrument state must be attained.
Before the data are passed on to the hardware, the settling bit in the STATus:OPERation
register is set. The hardware makes the settings and resets the bit when the new state has
settled. This procedure can be used for synchronization of command processing.
Status Reporting System
The status reporting system collects information on the instrument state and makes it
available to the output unit on request. A detailed description of the structure and
function is given in Chapter 2.
Output Unit
The output unit collects the information requested by the controller and output by the data
set management. The output unit processes the information in accordance with the SCPI
rules and makes it available in the output buffer. The output buffer has a size of 2048
characters. If the requested information exceeds this size, it is made available in portions
without this being recognized by the controller.
If the instrument is addressed as a talker without the output buffer containing data or
awaiting data from the data set management, the output unit returns the error message
"Query UNTERMINATED" to the status reporting system. No data are sent on the
interface. The controller waits until it has reached its time limit. This procedure is
specified by SCPI.
Interface queries cause the data set management to send the desired data to the output
unit.