# PLC Program to Implement 8 to 3 Encoder

This is a PLC Program to Implement 8 to 3 Encoder.

Problem Description

Implement 8 to 3 line encoder in PLC using Ladder Diagram programming language.

Problem Solution
• It has 8 inputs I0 to I7 and 3 outputs Q0 to Q3.
• These inputs I0 to I7 determines which output should be active.
• If I2 is true that means input 2 is selected. Output of 2 is 011 in binary hence outputs Q1 and Q2 will go high and Q0 remains in its low state.
• It does not need K-map and simplification so one step is eliminated to create Ladder Logic Diagram.
• Realize the 8 to 3 line encoder using Logic Gates.

Truth Table can be written as given below.

```Inputs	Outputs
Q0	Q1	Q2
I0=1	0	0	0
I1=0	0	0	1
I2=1	0	1	0
I3=1	0	1	1
I4=1	1	0	0
I5=1	1	0	1
I6=1	1	1	0
I7=1	1	1	1```

Realization of 3 to 8 line decoder using Logic Gates

PLC Program

Here is PLC program to Implement 8 to 3 Encoder, along with program explanation and run time test cases.

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```List of Inputs and Outputs
I0=		I:1/0	(Input)
I1=		I:1/1	(Input)
I2=		I:1/2	(Input)
I3=		I:1/3	(Input)
I4=		I:1/4	(Input)
I5=		I:1/5	(Input)
I6=		I:1/6	(Input)
I7=		I:1/7	(Input)
Q0=		O:2/0	(Output)
Q1=		O:2/1	(Output)
Q2=		O:2/2	(Output)```

Ladder Diagram for 8 to 3 line encoder

Program Description
• As we can see that Q0 O:2/0 is active whenever I4 I:1/4 to I7 I:1/7 inputs are pressed because in 3bit addresses, 1st bit goes high only when “input > integer 3 (011)”.
• Similarly Output Q1 O:2/1 goes high in two conditions, 1 < Input < 4 and 5 < Input < 8.
• And Output Q2 O:2/2 goes high whenever Odd number is given in input, i.e. here 1, 3, 5, 7.
• So basically in I7 I:1/7, all the inputs go true and in I0 I:1/0, all the outputs remain false.
Runtime Test Cases
```Inputs	Outputs
Q0	Q1	Q2
I0=1	0	0	0
I1=1	0	0	1
I2=1	0	1	0
I3=1	0	1	1
I4=1	1	0	0
I5=1	1	0	1
I6=1	1	1	0
I7=1	1	1	1```

Sanfoundry Global Education & Learning Series – PLC Algorithms.
To practice all PLC programs, here is complete set of 100+ PLC Problems and Solutions.

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If you find any mistake above, kindly email to [email protected]

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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