Rohde & Schwarz 1145.1010.04/05/06, Operating Manual

Page: 446 / 813

Command Processing R&S
®
ZVA/ZVB/ZVT
1145.1084.12 5.14 E-1
Command Processing
Command ProcessingThe block diagram below shows how GPIB bus commands are serviced in the
instrument.
The individual components work independently and simultaneously. They communicate with each other
by means of so-called "messages".
Input Unit
The input unit receives commands character by character from the GPIB bus and collects them in the
input buffer. The input unit sends a message to the command recognition as soon as the input buffer is
full or as soon as it receives a delimiter, <PROGRAM MESSAGE TERMINATOR>, as defined in IEEE
488.2, or the interface message DCL.
If the input buffer is full, the GPIB bus traffic is stopped and the data received up to then is processed.
Subsequently the GPIB bus traffic is continued. If, however, the buffer is not yet full when receiving the
delimiter, the input unit can already receive the next command during command recognition and
execution. The receipt of a DCL clears the input buffer and immediately initiates a message to the
command recognition.
Command Recognition
The command recognition stage analyzes the data received from the input unit. It proceeds in the order
in which it receives the data. Only a DCL is serviced with priority, e.g. a GET (Group Execute Trigger) is
only executed after the commands received before. Each recognized command is immediately
transferred to the data set but not executed immediately.
The command recognition detects syntax errors in the commands and transfers them to the status
reporting system. The rest of a command line after a syntax error is ignored.
If the command recognition detects a delimiter or a DCL, it also requests the data set to perform the
necessary instrument hardware settings. Subsequently it is immediately prepared to process further