EE101 - Digital Electronics Laboratory

Laboratory Exercise 4. Flip Flops



bulletTo study the fundamentals of basic memory units
bulletTo become familiar with various types of flip-flops
bulletTo implement a data register.


In this laboratory we will build on concepts that we examined in the previous laboratory sessions. We are now examining flip-flops. It is likely that we have not examined flip-flops in lectures at this point, but hopefully the laboratory exercise will help explain the concepts as we go along. This laboratory will examine your interpretation of what is occurring after you connect up the circuits. 


The equipment you require is as follows:

bulletYour lab notebook
bulletYour own lab kit (bought from the technicians).
bulletMinilab set, including Digital voltmeter (available at the desks)
bulletCollect hook-up wire and ICs from demonstrator.


The task that you must perform prior to sitting this laboratory:

bulletRead the laboratory assignment in full.

The Laboratory:

Section 1. The Asynchronous RS Flip-Flop

(a) Connect the two NOR gates as shown in Figure 1.

Figure 1. An RS Flip-Flop created using NOR gates.

(b) Vary the inputs R and S (i.e. 0 and +5V) to obtain all the possible combinations for Q and /Q.


(c) In your opinion why is there a Q and /Q output? In your opinion how does this circuit work?


Section 2. The Synchronous Flip-Flop

(a) Synchronous means that this flip-flop is concerned with time! Digital circuits can have a concept of time using a clock signal. The clock signal simply goes from low-to-high and high-to-low in a short period of time.

Figure 2. A typical clock signal.

Figure 3. The Synchronous Flip Flop.

Implement the circuit in Figure 3. You can simulate a clock signal by moving the clock line from low to high and back again to low.

(b) Vary inputs R and S and apply the clock pulse. Write the output states into a table as below:

Qn /Qn R S Qn+1 /Qn+1
0 1 0 0    
1 0 0 0    
0 1 0 1    
1 0 0 1    
0 1 1 0    
1 0 1 0    
0 1 1 1    
1 0 1 1    


(c) Convert the circuit into a D-type flip flop (as shown in Figure 4.)

Figure 4. The D-type flip-flop

Draw up the truth table for a D-type flip flop. In your opinion how does it work? what could this circuit be useful for?


Section 3. The J-K Flip-Flop

(a) Connect one of flip flops as shown in Figure 5. 

Figure 5. The JK flip-flop

Examine the operation of this flip-flop giving its outputs. 


Section 4. The Four Bit Data Register

(a) Connect up the four bit data register as shown in Figure 6. A JK Flip-flop can be used as a 1-bit memory by applying the bit to be stored to J, and its inverse to K. An n-bit binary word can be stored by n such flip-flops; called a n-bit register.

Figure 6. The 4-bit Data register

Connect the four flip-flops as shown in Figure 6. Connect a binary word to the data registers by connecting the inputs to lows and highs to insert whatever word you desire. Use a clock pulse to store this word. Reset the data register and store a new word. Describe what you did and what occurred?


(b) Is it possible to store a new word without resetting the register first? Why, or why not?


Section 5. Conclusions

(a) State briefly, but clearly, what you have gained from this laboratory. Outline aspects that you have noted within the experiment outside of the questions asked. Make comments on the procedure of the lab - Is there anything that you could have done differently? How did you split the work between group members? Did you have a plan of action? What else would you suggest that should be added to this lab session? What are flip-flops useful for (in your opinion)?


(b) Comments: Please write any comments that you may have here. Did you enjoy the lab? State one thing you would change? State one thing that you liked? Were there any problems during the laboratory session?





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EE101 Digital Electronics - Design and content developed by Derek Molloy. All documents and images ęDerek Molloy 1998-2006. Please do not reproduce anything from these pages without his expressed permission.