Rockwell Automation Logix5000 Controllers Sequential Function Charts Programming Manual - Manual (Page 19)

Design a sequential function chart Chapter 1
If you want to Then select or set this
member
Data type Details
Do something one time when the step
becomes active
FS 1 BOOL The FS bit is on during the first scan of the step.
Typically, we recommend that you use an action with a P1 Pulse (Rising Edge) qualifier
to accomplish this.
Do something while the step is active,
except on the first and last scan
SA BOOL The SA bit is on when the step is active except during the first and last scan of the step.
Do something one time on the last scan of
the step
LS 1 BOOL The LS bit is on during the last scan of the step.
Use this bit only if on the Controller Properties dialog box, SFC Execution tab, you
set the Last Scan of Active Step to Don’t Scan or Programmatic reset.
Typically, we recommend that you use an action with a P0 Pulse (Falling Edge) qualifier
to accomplish this.
Determine the target of an SFC Reset (SFR)
instruction
Reset BOOL An SFC Reset (SFR) instruction resets the SFC to a step or stop that the instruction
specifies.
The Reset bit indicates the step or stop where the SFC goes to begin executing again.
Once the SFC executes, the Reset bit clears.
Determine the maximum time that a step
has been active during any of its executions
TMax DINT Use this for diagnostic purposes. The controller clears this value only when you set
the Restart Position to Restart at initial step and the controller changes modes or
experiences a power cycle.
Determine if the Timer (T) value rolls over
to a negative value
OV BOOL Use this for diagnostic purposes.
Determine how many times a step has
become active
Count DINT This is not a count of scans of the step.
• The count increments each time the step becomes active.
• It increments again only after the step goes inactive and then active again.
• The count resets only if you configure the SFC to restart at the initial step. With that
configuration, it resets when the controller changes from program mode to run
mode.
Use one tag for the various status bits of
this step
Status DINT For this member Use this bit
Reset 22
AlarmHigh 23
AlarmLow 24
AlarmEn 25
OV 26
DN 27
LS 28
SA 29
FS 30
X 31
(1) The FS and LS bits are only active during a step’s execution. Once a step finishes executing the code within its actions, the FS or the
LS or both bits are reset. If you reference either of these bits in code outside of the SFC routine in a different part of the project, the
bits are always cleared (0).
Rockwell Automation Publication 1756-PM006F-EN-P - October 2014 19