User Manual DDS200 Digital Demodulation System 070-9952-00

Remote ControlInstrument Model and Command ProcessingThe instrument model shown in Figure 3–2 is configured under the aspect ofprocessing IEC/IEEE-bus commands. The individual components operateindependently of each other and simultaneously. They communicate with eachother by means of messages.IEC/IEEE–BusInput unit withinput bufferCommandidentificationData setDevice hardwareStatus reportingsystemIEC/IEEE–BusOnput unit withonput bufferFigure 3–2: Instrument model with remote control via IEC/IEEE busInput UnitThe input unit receives the commands in the form of characters from theIEC/IEEE bus and collects them in the input buffer. The input buffer has acapacity of 1024 characters. The input unit sends a message to the commandidentification as soon as the input buffer is full or as soon as it receives aterminator as defined by IEEE488.2 or the interface message DCL.If the input buffer is full, the data transfer from the IEC/IEEE bus is stopped andthe data received so far are processed. Data transfer from the IEC/IEEE bus isthen continued. If the buffer is not yet full when a terminator is received, theinput unit can receive the next command while the previous command isidentified and executed. Reception of a DCL command clears the input bufferand immediately causes a message to be sent to the command identification.Command IdentificationThe command identification analyzes the data received from the input unit,proceeding in the order in which the data are received. Only a DCL commandwill be given priority, whereas a GET (Group Execute Trigger) command will beprocessed when the previous commands have been executed. Each identifiedcommand will immediately be transferred to the data set, however, without beingimmediately executed there.3–16 DDS200 Digital Demodulation System User Manual