# Study of Flip Flops

Prior to the lab session:

1. Study the operation and working principle of RS, JK, D and T flip-flops.
2. Study the procedure for conducting the experiment in the lab.

Objectives:

To construct RS, JK, D and T flip-flops and verity their truth tables.

Apparatus:

1. IC 7476                                     -           1No.
2. IC Trainer kit                              -           1No.
3. Connecting patch chords

Theory:

In digital circuits, a FIip-FIop is a term referring to an electronic circuit (a bistable multivibrator) that has two stable states and thereby is capable of serving as one bit of memory. A flip-flop is usually controlled by one or two control signals and /or a gate or clock signal. The output often includes the complement as well as the normal output.

SR FIip-FIop:

The fundamental latch is the simple SR  flip-flop, where S and R stand for set and reset respectively. It can be constructed from a pair of cross-coupled NOR logic gates. The stored bit is present on the output marked Q.

Normally, in storage mode, the S and R inputs are both low, and feedback maintains the outputs in a constant state, with Q and the complement of Q. If S (Set) is given with high while R is held low, then the Q output is forced high, and stays high even after S returns low; similarly, if R (Reset) is given with high while S is held low, then the Q output is forced low, and stays low even after R returns low.

JK-FIip-FIop:

The JK flip-flop augments the behavior of the SR flip-flop (J = Set, K = Reset) by interpreting the S = R = 1 condition as a “flip“ or toggle command. Specifically, the combination J = 1, K = 0 is a command to set the flip-flop; the combination J = 0, K = 1 is a command to reset the flip-flop; and the combination J = K = 1 is a command to toggle the flip-flop, i.e., change its output to the logical complement of its current value.

D-FIip-FIop:

The Q output always  takes on the state of the D input at the moment of a rising clock edge. (or falling edge if the clock input is active low) It is called  the D flip-flop for this reason, since the output takes the value  of  the D input or Data input,  and Delays it by one clock count. The D flip-flop can be interpreted as a primitive memory cell, zero-order hold, or delay line.

T-FIip-FIop:

If the T input is high, the T flip-flop changes state (“toggles“) whenever the clock input is strobed. If the T input is low, the flip-flop holds the previous value. This behavior is described by the characteristic equation: A T flip-flop can also be built using a JK flip-flop (J & K pins are connected together and act as T) or D flip-flop.

Circuit diagrams:

RS FIip FIop Truth table
Inputs Outputs
R S Q
0 0 Indeterminate
0 1 1
1 0 0
1 1

Q0

(Previous state)

Fig.6.1 RS Flip-Flop basic version

Inputs Outputs
R S CLK Q
0 0 Q0
0 1 1
1 0 0
1 1 Indeterminate state
Fig.6.2 RS Flip-Flop Clocked version

Symbol:

JK FIip-FIop:

 Fig.6.3 JK Flip Flop using IC 7476(Power connection, ground connection, the above are two JK Flip-Flops in a single IC)

Truth table:

Inputs Outputs
Preset Clear Clock J K Q $\fn_cm \bar{Q}$
0 0 x x x 1 1
0 1 x x x 1 0
1 0 x x x 0 1
1 1 0 0 0 $\fn_cm \bar{Q}$
1 1 1 0 1 0
1 1 0 1 0 1
1 1 1 1 Toogle state
1 1 0 x x Q $\fn_cm \bar{Q}$

Symbol:

D-FIip-FIop using JK FIip-FIop:

Inputs Outputs
Preset Clear Clock D Q $\fn_cm \bar{Q}$
L H X X H L
H L X X L H
L L X X H H
H H H H L
H H L L H
H H L X Q0 $\fn_cm \bar{Q}_{0}$
Fig.6.4 D-Flip-Flop using JK Flip-Flop & its Truth table

Symbol:

T-FIip-FIop using JK FIip-FIop:

Inputs Outputs
Preset Clear Clock T Q $\fn_cm \bar{Q}$
L H X X H L
H L X X L H
L L X X H H
H H H Toogle state
H H L H L
H H L X Toogle state
Fig.6.5 T-Flip-Flop using JK Flip-Flop & its Truth table

Symbol:

Procedure:

1. Construct the RS flip flop as shown in figures 6.1 & 6.2.
2. Feed the logic signals from the logic input switches observe the logic outputs on the logic Level LED indicators.
3. Verify the corresponding truth tables.
4. Construct JK - flip flop (fig 6.3) and repeat step 2 and 3.
5. Construct D - Flip flop (fig 6.4) and repeat step 2 and 3.
6. Construct T - Flip flop (fig 6.5) and repeat step 2 and 3.

Inference:

Different types of Flip flops (RS, Clocked RS, JK, D, T) are Constructed using IC 7476 and hence their truth tables are verified.

Viva Questions:

1. Difference between latch and flip-flop.
2. List the applications of flip-flops.
3. Explain the operation of JK master slave flip-flop.
4. What is the difference between SR-flip flop  and clocked SR-FF.
5. What is meant by level triggering and edge triggering in flip-flops.
6. Explain the difference between +ve edge and -ve edge triggering.
7. Which type of edge triggering is used in IC 7476 J-K MIS Flip-flop?
8. Explain the preset and clear inputs of a flip-flop and why are these Called asynchronous Inputs.
9. What is meant by toggle and where do  the T-FF’s are used.
10. Where do the D-FF’s are used and why it is called a delay flip flop.
11. Explain the race around problem in JK-FF and how it is eliminated in master slave JK- FF.

Outcomes:

After finishing this experiment students are able to construct RS, JK, D and T flip-flops and verity their truth tables.

• Updated
Jan 07, 2014
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32,607
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