3 to 8 Line Decoder PLC Ladder Diagram

Implement 3 to 8 line decoder in PLC using ladder diagram programming language.

Problem Solution

For this problem, we will use S7-1200 PLC and TIA portal software for programming.

This decoder has three inputs and 8 outputs and these inputs determine which output will be ON.

Here three inputs were used (Input 1-I0.0, Input 2-I0.1, and Input 3-I0.2), and 8 outputs were used (Output 1 to 7, Q0.0 to Q0.7).

If all inputs are OFF, output 1 (Q0.0) will be ON and others are not.

List of inputs/outputs

List of inputs

• Input 1:- I0.0
• Input 2 :- I0.1
• Input 3 :- I1.0

List of outputs

• Output1 :- Q0.0
• Output 2 :- Q0.1
• Output 3 :- Q0.2
• Output 4 :- Q0.3
• Output 5 :- Q0.4
• Output 6 :- Q0.5
• Output 7 :- Q0.6
• Output 8 :- Q0.7

Program Description

For this application, we used S7-1200 PLC and TIA portal software for programming.

Network 1:

If all inputs are OFF (I0.0=0, I0.1=0 and I0.2=0), Output 1 (Q0.0) will be ON.

Network 2:

If input 1 (I0.0) and input 2 (I0.1) are OFF and input 3 (I0.2) is ON, Output 2 (Q0.1) will be ON.

Network 3:

If input 1 (I0.0) and input 3 (I0.2) are OFF and input 2 (I0.1) is ON, Output 3 (Q0.2) will be ON.

Network 4:

If input 2 (I0.1) and input 3 (I0.2) are ON and input 1 (I0.0) is OFF, Output 4 (Q0.3) will be ON.

Network 5:

If input 2 (I0.1) and input 3 (I0.2) are OFF and input 1 (I0.0) is ON, Output 5 (Q0.4) will be ON.

Network 6:

If input 1 (I0.0) and input 3 (I0.2) are ON and input 2 (I0.1) is OFF, Output 6 (Q0.5) will be ON.

Network 7:

If input 1 (I0.0) and input 2 (I0.1) are ON and input 3 (I0.2) is OFF, Output 7 (Q0.6) will be ON.

Network 8:

If input 1 (I0.0) and input 2 (I0.1) and input 3 (I0.2) are ON, Output 8 (Q0.7) will be ON.

Note :- Above application may be different from actual application. This example is only for explanation purpose only. We can implement this logic in other PLC also. This is the simple concept of 3 to 8 line decoder, we can use this concept in other examples also.

All parameters considered in example are for explanation purpose only, parameters may be different in actual applications. Also all interlocks are not considered in the application.

Author: Bhavesh