How To Invert The Logic Of An Output - Alternate Circuit

September 26, 2011
By Anonymous

Inverting The Logic Of An Output

Inverting the logic of an output by using the ON state of an input can simplify programming logic. This allows optimization with only one sensor connected to the PLC. Whenever the leading edge of input signal (X0) is detected, the state of output (Y10) is reversed. The operation can be easily achieved by using Alternative Out (ALT) instruction as follows. Engineers who have used FPWin GR software and now switching to FPWin Pro (IEC 61131-3 Programming System) may have difficulties performing the same alternate instruction. Below are some examples that cover the use of the alternate instruction.


Ladder Logic FPWin GR

FPWin Pro

(direct addressing)

Ladder Logic FPWinPro

Using Global Variables


Global Variables

Time Chart

Time Chart

Please note:

Alternate instruction is not supported for FP0 and older PLC models. (FP1, FP3 and FP-M, etc.) You need to implement the logic below to alternate PLC output.

Alternate Instruction

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