CMU Instrument Model and Command Processing
1100.4903.12 5.15 E-8
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 sends error message "Query UNTERMINATED" to the status
reporting system. No data are sent on the GPIB bus, the controller waits until it has reached its time
limit. This behavior is specified by SCPI.
Command Sequence and Command Synchronization
What was said above makes clear that overlapping execution is possible in principle for all commands.
Equally, setting commands within one command line are not absolutely serviced in the order in which
they have been received.
In order to make sure that commands are actually carried out in a certain order, each command must
be sent in a separate command line, that is to say, with a separate IBWRT()-call.
In order to prevent an overlapping execution of commands, one of commands *OPC, *OPC? or *WAI
must be used. All three commands cause a certain action only to be carried out after the hardware has
been set and has settled. By a suitable programming, the controller can be forced to wait for the re-
spective action to occur (cf. Table 5-1).
Table 5-1 Synchronization with *OPC, *OPC? and *WAI
Com-
mand
Action after the hardware has settled Programming the controller
*OPC Setting the operation-complete bit in the ESR - Setting bit 0 in the ESE
- Setting bit 5 in the SRE
- Waiting for service request (SRQ)
*OPC? Writing a "1" into the output buffer Addressing the instrument as a talker
*WAI Executing the next command
Note: The GPIB bus handshake is not stopped
Sending the next command
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