Select (SEL)
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 Select (SEL) instruction uses a digital input to select one of two inputs.
Available Languages
Ladder Diagram
This instruction is not available in ladder diagram logic.
Function Block
Structured Text
This instruction is not available in structured text.
Operands
Function Block
Operand | Type | Format | Description |
SEL tag | SELECT | structure | SEL structure |
SELECT 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. |
In1 | REAL | The first analog signal input to the instruction.
Valid = any float
Default = 0.0 |
In2 | REAL | The second analog signal input to the instruction.
Valid = any float
Default = 0.0 |
SelectorIn | BOOL | The input that selects between In1 and In2.
Default is cleared. |
Output Parameter | Data Type | Description |
EnableOut | BOOL | Indicates if instruction is enabled. Cleared on overflow. |
Out | REAL | The calculated output of the algorithm. |
Description
The SEL instruction operates as follows:
Condition | Action |
SelectorIn is set | Out = In2 |
SelectorIn is cleared | Out = In1 |
Affects Math Status Flags
No
Major/Minor Faults
None specific to this instruction. See Common Attributes 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 | Out n-1 is set to 0. |
Postscan | N/A |
Example
The SEL instruction selects In1 or In2 based on SelectorIn. If SelectorIn is set, the instruction sets Out = In2. If SelectorIn is cleared, the instruction sets Out = In1. Out becomes an input parameter for function_block_C.
Function Block
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