B&K Precision MDL Series - Programming Manual - Manual (Page 25)

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that contains four single item query commands:
0; 1; 1; 0
Response Message Terminator (RMT)
Each response is terminated with an LF (line feed) and EOI (end or identify). The following example
shows how a multiple response message is terminated:
0; 1; 1; 0;
Message Exchange Protocol
Two rules summarize the message exchange protocol:
Rule 1. You must always tell the electronic load what to send to the computer.
The following two steps must always be performed to send information from the
computer to the instrument:
1) Send the appropriate query command(s) in a program message.
2) Address the electronic load to talk.
Rule 2. The complete response message must be received by the computer before another
program message can be sent to the electronic load.
2.4 SCPI Command Completion
SCPI commands sent to the electronic load are processed either sequentially or in parallel. Sequential
commands finish execution before a subsequent command begins. Parallel commands allow other
commands to begin executing while the parallel command is still executing. Commands that affect
trigger actions are among the parallel commands.
The *WAI, *OPC, and *OPC? common commands provide different ways of indicating when all
transmitted commands, including any parallel ones, have completed their operations. The syntax and
parameters for these commands are described in Chapter 4. Some practical considerations for using
these commands are as follows:
*WAI This prevents the electronic load from processing subsequent commands until all pending
operations are completed.
*OPC? This places a 1 in the Output Queue when all pending operations have completed. Since it
requires your program to read the returned value before executing the next program
statement, *OPC? can be used to cause the controller to wait for commands to complete
before proceeding with its program.