User`s manual

In an instrument where the previous commands are coupled, sending the
commands as shown prevents "Settings conflict" errors. The command
settings are not evaluated until the EOL terminator is received after the last
command. If these commands were sent individually (an EOL terminator
after each command), a "Settings conflict" error would occur because of the
coupling between OUTP:EXT1:STAT ON and TRIG:SOUR EXT1.
DEBUG9 : Check for Command Synchronization Errors
IEEE 488.2 specifies that all instruments will have an input buffer and that
execution of these commands does not start until a program message
terminator is received (i.e. Line Feed, Line Feed with EOI, or EOI).
A common problem is the computer will send commands to the input
buffers of two instruments. It is possible that the second instrument may
execute its commands before the first instrument executes the commands.
Thus, instruments may execute their functions in an order that is different
from the command sequence in the computer program.
Synchronization of instrument-to-computer is accomplished by sending a
command that returns data. The computer must wait for the data to be
returned. The *OPC? command defined by IEEE 488.2 was created for this
purpose. *OPC? will return a one (1) when the commands before it have
finished executing.
The following example closes four relays and waits for the command to
complete before continuing with the next command:
CLOSE (@100,101,102,103);*OPC?
/* enter the data returned by *OPC? (1) */
READ?
C-Size Configuration Guide System Programming and Debugging 6-13