American Magnetics 187 Self-Compensating Liquid Level Controller - Manual (Page 48)

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Remote Interface Reference
Command Handshaking
4.2.5.1 Using the *OPC Command
The *OPC command is executed within the normal command queue. Upon
completed execution of the *OPC command, the “Operation Complete” bit
(bit 0) of the Standard Event register will be set.
If the operator has so configured the Standard Event and Status Byte
enable registers, the
*OPC command can generate an IEEE-488 service
request when execution completes (see Figure 4-1). If using the serial port,
the
*OPC? query is a better alternative since a response is returned
directly to the requesting communications interface.
An example of a sequence of commands using the *OPC command to
handshake is the following:
PERCENT; CONF:ALARM:A 50.0; CONF:ALARM:B 20.0; *OPC;
The above example sets the remote units to percent, the “A” alarm to
50.0%, the “B” alarm to 20.0%, and sends
*OPC as the 4th command for
determining when execution all of the commands (including *OPC ) has
completed. If the Standard Event and Status Byte enable registers are
correctly configured, the
*OPC command will then result in an IEEE-488
service request when execution completes. Alternately, the Serial Poll
function of the IEEE-488 bus may be used to determine completion of the
command.
4.2.5.2 Using the *OPC? Query
The *OPC? query is similar to the *OPC command, but instead of setting
the “Operation Complete” bit of the Standard Event register, the *OPC?
query returns a “1” (plus termination characters) to the requesting remote
interface when executed. Using
*OPC? is often the most straightforward
solution for determining completed command execution. It is also
unambiguous since the result is returned directly to the requesting remote
communication interface.
4.2.6 Remote Units
The Model 187 supports a remote units setting that is maintained
separately from the units selected via the front panel keypad. The remote
units setting is retained between power-ups. If the
PERCENT command is
sent to the remote interface, the remote units for both remote interfaces is
set to percent. All alarm values should then be sent as a percent value, and
all return level data and alarm queries are returned in units of percent.
The UNITs? query returns the currently selected remote units, e.g. the
percent setting would return 0,”PERCENT” .