One Shot Falling with Input (OSFI)

This information applies to the
CompactLogix
5370,
ControlLogix
5570,
Compact GuardLogix
5370,
GuardLogix
5570,
Compact GuardLogix
5380,
CompactLogix
5380,
CompactLogix
5480,
ControlLogix
5580, and
GuardLogix
5580 controllers.
The One Shot Falling with Input (OSFI) instruction sets the OutputBit for one execution cycle when the InputBit toggles from false to true.
Available Languages
Ladder Diagram
This instruction is not available in ladder diagram.
Function Block
OSFI_LD_avail_v31
Structured Text
OSFI(OSFI_tag)
Operands
Structured Text
Operand
Type
Format
Description
OSFI tag
FBD_ONESHOT
Structure
OSFI structure
See Structured Text Syntax for operand-related faults
Function Block
Operand
Type
Format
Description
OSFI tag
FBD_ONESHOT
Structure
OSFI structure
FBD_ONESHOT Structure
Input Parameter
Data Type
Description
EnableIn
BOOL
Enable input. If cleared, the instruction does not execute and outputs are not updated.
Default is set.
InputBit
BOOL
Input bit.
Output Parameter
Data Type
Description
EnableOut
BOOL
Indicates if instruction is enabled.
OutputBit
BOOL
Output bit
Description
If InputBit is false, and it was true the last time the instruction was scanned then OutputBit will be set, otherwise OutputBit will be cleared.
Affects Math Status Flags
No
Major/Minor Faults
None specific to this instruction. See for operand-related faults.
Execution
Function Block
Condition / State
Action Taken
Prescan
EnableIn and EnableOut bits are cleared to false.
Tag.EnableIn is false
EnableIn and EnableOut bits are cleared to false.
Tag.EnableIn is true
EnableIn and EnableOut bits are set to true.
The instruction executes
Instruction first run
N/A
Instruction first scan
Previous InputBit history is cleared to require a True to False transition of InputBit.
Postscan
EnableIn and EnableOut bits are cleared to false.
Structured Text
Condition / State
Action Taken
Prescan
See Prescan in the Function Block table.
Normal execution
See Tag.EnableIn is true in the Function Block table.
Postscan
See Postscan in the Function Block table.
Example
When limit_switch1 goes from set to cleared, the OSFI instruction sets OutputBit for one scan.
Function Block
Structured Text
OSFI_01.InputBit := limit_switch1;
OSFI(OSFI_01);
Output_state := OSFI_01.OutputBit;
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