One Shot Falling (OSF)
The OSF instruction sets the output bit for one scan when rung-condition-in transitions from true to false.
Available Languages
Ladder Diagram
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Operands
IMPORTANT:
Unexpected operation may occur if:
- Output tag operands are overwritten
- Members of a structure operand are overwritten
- Except when specified, structure operands are shared by multiple instructions.
Ladder Diagram
Operand | Data Type | Format | Description |
|---|---|---|---|
Storage Bit | BOOL | tag | Stores the rung-condition-in from when the instruction was last executed. There are various operand addressing modes possible for the storage bit, see Bit Addressing for examples. |
Output Bit | BOOL | tag | Bit to be modified. |
Affects Math Status Flags
No
Major/Minor Faults
None specific to this instruction. See Index through arrays for array-indexing faults.
Execution
Ladder Diagram
Condition/State | Action Taken |
|---|---|
Prescan | The storage bit is cleared to false to prevent an invalid trigger during the first program scan. The output bit is cleared to false. |
Rung-condition-in is false | Set Rung-condition-out to Rung-condition-in. See OSF Flow Chart (False). |
Rung-condition-in is true | Set Rung-condition-out to Rung-condition-in. The storage bit is set to true. The output bit is cleared to false. |
Postscan | N/A |
OSF Flow Chart (False)
Example
Ladder Diagram
This example shows how an OSF can be used to make one or more instructions edge-triggered. Each time Limit_Switch_01 transitions from true to false the OSF will set Output_bit_02 to true. Any instruction conditioned by Output_bit_02 will be enabled and, since Output_bit_02 is only true for one scan, will execute once per transition.
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