Design a sequential function chart
Rockwell Automation Publication 1756-PM006I-EN-P - February 2018 49
If the stop element is at the end of a Then
• Selection branch
The entire SFC stops
Path within a simultaneous branch
Only that path stops while the rest of the SFC continues to
execute.
Example
Use a stop element on page 48
When the SFC reaches last_step and process_done is TRUE, the execution of the
SFC stops.
Once at the stop element, you have several options to restart the SFC.
If the SFC is
And the Last Scan of the Active Steps
option is
Then
Nested (i.e., another SFC calls this SFC as a
subroutine)
Automatic reset
At the end of the step that calls the nested SFC, the nested SFC automatically resets.
• The nested SFC resets to the initial step.
• The X bit of the stop element in the nested SFC clears to zero.
Programmatic reset
• Don’t scan
1. Use an SFC Reset (SFR) instruction to restart the SFC at the required step.
2. Use logic to clear the X bit of the stop element.
Not nested (i.e., no SFC calls this SFC as a
subroutine)
-------------------------------> 1. Use an SFC Reset (SFR) instruction to restart the SFC at the required step.
2. Use logic to clear the X bit of the stop element.
Example
This example shows the use of the SFC Reset (SFR) instruction to restart the SFC
and clear the X bit of the stop element (see Restart (reset) the SFC on page 49).
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