Allen-Bradley Logix5000 Reference Manual page 108

Chapter 2 Bit Instructions (XIC, XIO, OTE, OTL, OTU, ONS, OSR, OSF, OSRI, OSFI)
Condition
Prescan.
Rung-condition-in is false.
Storage bit is cleared.
Output bit is set.
Rung-condition-out is
Rung-condition-in is true.
Postscan.
108
Execution:
Relay Ladder Action
The storage bit is cleared to prevent an invalid trigger during the first scan.
The output bit is cleared.
The rung-condition-out is set to false.
Storage Bit = 0
Examine
storage bit.
Storage Bit = 1
set to false.
The storage bit is set.
The output bit is cleared.
The rung-condition-out is set to true.
See rung-condition-in is false above.
Example:
Each time limit_switch_1 goes from set to cleared, the OSF instruction sets
output_bit_2 and the ADD instruction increments sum by 5. As long as
limit_switch_1 stays cleared, sum stays the same value. The limit_switch_1 must
go from set to cleared again for sum to be incremented again. You can use
output_bit_2 on multiple rungs to trigger other operations.
Rockwell Automation Publication 1756-RM003N-EN-P - October 2011
Storage bit remains
cleared.
Output bit is cleared.
Rung-condition-out is
set. to false.
End