csmstr - Omega Engineering

PROGRAM PROPERTIES
CRIMSON USER MANUAL - MODULAR CONTROLLER
the value of that calculation to the user. Programs that return values are
described in more detail below.
• The Run In Background property is used to indicate whether Crimson should
wait for the program to complete execution before continuing with processing
whatever task invoked the program. For example, if this property is set to No,
running a program in response to a key being pressed will result in a pause in
display updates until the program completes. (Since most programs take very
little time to execute, this may not even be noticeable.) If this property is set to
Yes, display updates will continue immediately, and the program will execute at
a lower priority in the background. Only one background program will run at
once, so subsequent requests are queued for later execution. Note also that
programs that return values cannot be run in the background, as their return
value would then not be available for the caller to use!
• The External Data and Timeout properties are used to control how the program
interacts with Crimson’s communication infrastructure with respect to external
data items to which the program makes reference. You will recall that Crimson
only reads data items when they are used. This property is used to control the
exact interpretation of this rule with respect to programs…
MODE
Read When Referenced
Read Always
Read When Executed
Read But Run Anyway
BEHAVIOR
External data used by the program will be added to the
comms scan whenever the program is referenced. If the
program is referenced by a display page, the data will be
read when that page is displayed; if the program is
referenced by a global action or a trigger, the data will be
read at all times. This is the default mode, and is
acceptable for all programs, except those that use very
large amounts of external data.
External data used by the program will be read at all
times, whether or not the program is referenced. This
means that the program will always be ready to run, and
that the operator will not see the “NOT READY” message
that might otherwise occur when the program is first
referenced. The downside of this mode is that comms
performance may be reduced if large amounts of data are
referenced by the program.
External data used within the program will be read only
when the program is invoked. The program will wait for
the period defined in the timeout property for such data to
be available. If the data cannot be read—perhaps because
a device is offline—the program will not execute. This
mode is typically used with globally-referenced programs
that consume large amounts of data that would otherwise
slow down the communications scan.
External data will be treated as described for Read Always
mode, but the program will execute whether or not the
data has been read successfully. The operator will
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