Conversion of Flip Flops

Contents

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Key learnings:

Flip Flop Conversion Definition: Flip flop conversion is defined as the process by which one type of flip flop is modified to perform as another type, involving adjustments to its circuitry and logic.
Truth Table Role: Understanding the truth table of both the original and target flip flops is crucial as it dictates the necessary inputs and expected outputs.
Excitation Table Usage: The excitation table reveals the required inputs to achieve specific states, facilitating the conversion process.
Logical Simplification: Simplifying the input expressions, often using K-maps, is essential for efficiently converting flip flops.
Practical Conversion Steps: The steps include designing truth tables, creating excitation and conversion tables, simplifying logic, and finalizing the circuit design, demonstrating the methodical approach to the conversion of flip flops.

Flip-flop conversion is the process of making one type of flip-flop behave as another by adding input gates or new connections. The five steps below convert a JK cell to an SR cell. The same method is used for the other pairs later on this page.

Conversion of JK Flip-Flop to SR Flip-Flop

Step 1: Write the Truth Table of the Desired Flip-Flop
To build an SR flip-flop from a JK flip-flop, write the SR flip-flop truth table first.

Step 2: Obtain the Excitation Table for the given Flip-Flop from its Truth Table
An excitation table lists the inputs that take a flip-flop from the present state Q_n to the next state Q_n+1.

The JK truth table shows Q_n+1 stays 0 when Q_n = 0 if (i) J = K = 0 or (ii) J = 0 and K = 1 (blue entries in the first and third rows).

So to get Q_n+1 = 0 from the current state Q_n = 0, J must be 0. K may be 0 or 1.

That is the first excitation-table row (blue entries): K is written as X, a don’t-care. To go from 0 to 1, J must be 1 and K may be 0 or 1 (green truth-table entries).

The second excitation-table row (green) is therefore Q_n = 0, Q_n+1 = 1, J = 1 and K = X. The pink and dark-red rows are filled the same way.

Step 3: Append the Excitation Table of the given Flip-Flop to the Truth Table of the Desired Flip-Flop Appropriately to obtain Conversion Table
Fill J and K for each Q_n and Q_n+1 from the excitation table. That combined sheet is the conversion table.

Step 4: Simplify the Expressions for the Inputs of the given Flip-Flop
Express J and K in terms of S, R and Q_n. A K-map is the usual tool.

Step 5: Design the Necessary Circuit and make the Connections accordingly
JK already covers every SR input pair, so this conversion needs no extra gates.
The same five steps convert the other flip-flop pairs shown below.