Rockwell Automation Logix5000 Controllers Sequential Function Charts Programming Manual - Manual (Page 33)

Design a sequential function chart Chapter 1
Call a subroutine.
Check for the required conditions. When those conditions are TRUE, turn on a BOOL tag.
Use an EOT instruction to set the state of the transition equal to the value of the BOOL tag. When the BOOL tag
is on (TRUE), the transition is TRUE.
Each step of the SFC includes a millisecond timer that runs whenever the step is
active. Use the timer to for these situations.
• Signal when the step has run for the required time and the SFC should go
to the next step.
• Signal when the step has run too long and the SFC should go to an error
step.
The following shows the action of a timer and associated bits of a step.
Description
Step becomes active.
X bit turns on.
Timer (T) begins to increment.
Timer reaches the Preset (PRE) value of the step.
DN bit turns on.
Timer continues to increment.
Step becomes inactive.
X bit turns off.
Timer retains its value.
DN remains on.
Transition after a specified
time
Rockwell Automation Publication 1756-PM006F-EN-P - October 2014 33