Design a sequential function chart
Rockwell Automation Publication 1756-PM006I-EN-P - February 2018 23
This diagram shows the relationship of the X, FS, SA, and LS bits.
Once you define the steps of your process, organize them into sequences,
simultaneous branches, selection branches, or loops.
To Use this structure With these considerations
Execute 1 or more steps in sequence
• One executes repeatedly
• Then the next executes repeatedly
Sequence on page 25
The SFC checks the transition at the end of the step.
• If TRUE the SFC goes to the next step.
• If FALSE, the SFC repeats the step.
• Choose between alternative steps or groups of steps
depending on logic conditions
• Execute a step or steps or skip the step or steps
depending on logic conditions
Selection Branch on page 25
• It is OK for a path to have no steps and only a transition.
This lets the SFC skip the selection branch.
• By default, the SFC checks from left to right the transitions
that start each path. It takes the first TRUE path.
• If no transitions are TRUE, the SFC repeats the previous
step.
• The Logix Designer application lets you change the order in
which the SFC checks the transitions.
Execute 2 or more steps at the same time. All paths must
finish before continuing the SFC
Simultaneous Branch on page 26
• A single transition ends the branch.
• The SFC checks the ending transition after the last step in
each path has executed at least once. If the transition is
FALSE, the SFC repeats the previous step.
Organize the steps
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