D Flip Flop PLC Ladder Logic

This is the PLC Program to implement D flip flops in PLC. Learn PLC programming based on simple digital electronics examples.

D Flip Flop PLC Ladder Logic

Problem Description

Implement D flip flop in PLC using ladder language programming.

Problem Diagram

Problem Solution

D flip flop has one input which denoted with D. D latch is simple flip flop with NAND gate circuit between S and R input.

In SR flip flop when S=R=1 and S=R=0, outputs either do not change or they are invalid (no action).

As we can see in diagram in D flip flop S and R inputs always be the complements of each other. Hence S=R=1 and S=R=0 conditions will never occur.

This disadvantage of the SR flip flop can be overcome by using D flip flop.

Truth Table for the D Latch

List of inputs and outputs

Digital Inputs

• SET/RESET :- I0.0

Digital outputs

• Q output :- Q0.0
• Q^ output :- Q0.1

M memory

• Relay coil 1 :- M0.0
• Relay coil 2 :- M0.1

PLC Ladder Diagram for D-Flipflop

Program Description

For this application, we use S7-300 PLC and TIA portal software for programming. We can implement this logic by using other PLC also.

Network 1:

Here we used NO contact of SET/RSET input (I0.0) and in parallel connection we used NC contact of relay coil 2 (M0.1) to operate relay coil 1 (M0.0).

Network 2:

Here we used NC contact of SET/RSET input (I0.0) and in parallel connection we used NC contact of relay coil 1 (M0.0) to operate relay coil 2 (M0.1).

Network 3:

When relay coil 1 (M0.0) is ON, Q output (Q0.0) will be ON.

Network 4:

When relay coil 2 (M0.1) is ON, Q^ output (Q0.1) will be ON.

As per D flip flop, a condition of Q=1 and Q^=0 is set and a condition of Q=0 and Q^=1 is reset.

Here we can see in diagram as well as in ladder diagram, difference in D flip flop and SR flip flop is that it uses inverted value of S input.

So in D flip flop we are using only one in put for SET/RESET.

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 D flip flop.

All parameters considered in example are for explanation purpose only, parameters may be different in actual applications.

Result

Author: Bhavesh

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