SEL

SEL selects one of two input values and writes it to Result according to the state of Selector.

Ladder Representation

Variable Table

Variable Type	Name	Data Type	Description
VAR_INPUT	EN	BOOL	Enables block execution.
VAR_INPUT	Selector	BOOL	Selects which input is copied to the output.
VAR_INPUT	Value0	BYTE USINT SINT WORD UINT INT DWORD UDINT DINT REAL STRING	First input value.
VAR_INPUT	Value1	BYTE USINT SINT WORD UINT INT DWORD UDINT DINT REAL STRING	Second input value.
VAR_OUTPUT	ENO	BOOL	Indicates the end of the operation.
VAR_OUTPUT	Result	BYTE USINT SINT WORD UINT INT DWORD UDINT DINT REAL STRING	Selected output value.

Operation

When EN is TRUE, SEL writes Value0 to Result when Selector is FALSE. When Selector is TRUE, SEL writes Value1 to Result.

When EN is FALSE, Result remains unchanged.

ENO passes the EN value to the next Ladder block after the operation finishes.

Execution Flowchart

Examples

Ladder Example

In this example, SELECTOR is FALSE, so RESULT receives VALUE0. The block finishes successfully and activates ENO.

This example also uses SELECTOR as the selection input. With SELECTOR at FALSE, RESULT receives VALUE0. The binary pattern is preserved even though the decimal representation is not valid for negative values in DWORD.

In this example, SELECTOR is TRUE, so RESULT receives VALUE1. The binary pattern is preserved even though the decimal representation is not valid for negative values in DWORD.

Structured Text Example

The following Structured Text example applies the same selection logic.

Structured Text

VAR
    SELECTOR : BOOL := FALSE;
    VALUE0 : SINT := _52;
    VALUE1 : INT := _985;
    RESULT : INT;
END_VAR

RESULT := FB_SEL(
    EN:=DI1,
    Selector:=SELECTOR,
    Value0:=VALUE0,
    Value1:=VALUE1,
    ENO=>DO1);