Emerson Micro Motion 3711, Configuration And Use Manual, Page: 118 / 234

110 Micro Motion
®
Model 3711 Gas Flow Computers
Function Sequence Tables
11.5 Developing an FST
This section provides instructions for developing an FST.
Before beginning FST development, review the following requirements and guidelines:
• An END command is required at the end of every FST. The END command tells the FST to
return to the top of the first STEP and begin to run from the first line at STEP 0. However, you
can use a branching function to force the FST to return to STEP 0 immediately if you do not
want to wait for the next execution cycle to begin.
• The first blank line found in an FST is treated as an END command. Any commands following
a blank line are lost.
• Only one END command can be present in an FST.
• Use Wait states (the WT command) to suspend operation of the FST whenever possible to
reduce MPU processor overload, especially in a loop in which a condition is being checked
repeatedly.
• When executing a loop repeatedly in an FST, include a timer (the ST and CT commands) so
that the loop executes only once every 100 milliseconds. This prevents the loop from executing
several times within the allotted task period, eliminating unnecessary calculations that could
deprive time from other tasks.
• Be sure to configure the I/O parameters before referencing them in an FST.
• When using any branching command (GO, <, >, <=, >=, ==), make sure that you have defined
the LABEL that you are referencing with the command.
• While developing an FST, save your work to a file at frequent intervals (see Step 6).
• Because of the potential loading increase on the system, it is recommended that you monitor
the Master Processor Unit (MPU) loading to ensure that the FST is not consuming too much of
the MPU's resources (see Section 15.7). It is good practice to insert WT commands or make
sure an END command is encountered to reduce processor loading.
Step 1 Define the FST functions
Define all the functions that will be required by your FST. Each function includes:
• A step number
• A label (optional)
• A command
• Zero, one or two arguments, as required by the command
Each FST must begin with Step 0 and use steps sequentially. A blank step is treated as an END.