1756-PM003H-EN-E, SFC and ST Programming Languages ...

Design a Sequential Function Chart 4-11
Organize the Steps
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
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
Execute 2 or more steps at the same time.
All paths must finish before continuing the
SFC
Selection Branch
Simultaneous Branch
• 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.
• RSLogix 5000 software lets you change
the order in which the SFC checks the
transitions.
• 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.
Loop back to a previous step Wire to a Previous Step • Connect the wire to the step or
simultaneous branch to which you want
to go.
• Do not wire into, out of, or between a
simultaneous branch.
Publication 1756-PM003H-EN-E (excerpt from 1756-PM001H-EN-P) - August 2005