Rockwell Automation Logix5000 Controllers Add-on Instructions Programming Manual - Manual (Page 53)

Defining Add-On Instructions Chapter 2
Postscan routine
Postscan mode occurs only for logic in a Sequential Function Chart Action when
the Action becomes inactive and the SFC language is configured for Automatic
Reset (which is not the default option for SFC). When an SFC Action becomes
inactive, then the logic in the Action is executed one more time in Postscan mode.
This mode is similar to Prescan in that most instructions simply execute as if they
have a false condition. It is possible for an instruction to have different behavior
during Postscan mode than it has during Prescan mode.
When an Add-On Instruction is called by logic in an SFC Action or a call resides
in a routine called by a JSR from an SFC Action, and the Automatic Reset option
is set, the Add-On Instruction executes in Postscan mode. The primary logic
routine of the Add-On Instruction executes in Postscan mode. Then if it is
defined and enabled, the Postscan routine for the Add-On Instruction executes.
This could be useful in resetting internal states, status values, or de-energizing
instruction outputs automatically when the action is finished.
Tip: Because safety Add-On Instructions cannot be called from an SFC Action, this option is disabled for safety
Add-On Instructions.
Follow these steps to create a postscan routine.
1. In the Controller Organizer, right-click an instruction and select Open
Definition.
2. Click the Scan Modes tab.
3. Click New for Postscan Routine.
Rock well Automati on Publication 1756- PM010F-EN-P - Oct ober 2014 53