Excelsior College
ELEC201 Digital Electronics Module 3: Laboratory 2B: Shift Registers
Objectives The objectives of this experiment are to:

• Examine how flip flops are combined to make shift registers.
Examine the operation of a pseudorandom number generator. Introduction The same flip flops that can be used to make a counter can be used to make a shift register. The
difference is how the flip flops are clocked and what mode they operate in. In this exercise we
will examine several shift register circuits and applications.
Procedure 1. Load the circuit E6B-1.MS7, shown in Figure 6B.1. Figure 6B.1: 4-bit D-type shift register
2. Press the ‘D’ key slowly and irregularly to load different patterns into the shift register. Now
and then press the ‘C’ key and see what happens.
3. How many clock pulses does it take for a bit to move through the shift register?
4. Convert the 4-bit D-type shift register into a 4-bit JK-type shift register. Sme hints:

• Connect Q of one stage to J on the next stage.
Connect Q’ on one stage to K on the next stage.
Page 1 of 4 Module 3: Laboratory 2B: Shift Registers •
• Clock all flip flops at the same time.
The J and K inputs on the first flip flop should always be different. 5. Compare the way data is clocked into the D-type shift register with that of the JK flip flop
shift register.
6. Load the circuit E6B-2.MS7, shown in Figure 6B.2. Figure 6B.2: 74195 parallel-load shift register
7. Simulate the circuit. The shift register should eventually fill with 1s. When this happens, press
‘L’ once. Does the output instantly change to a new pattern? After a few seconds, press ‘L’
again. Now what happens? Examine the help information for the 74195 to see how the shift/load
input operates.
8. Load the circuit E6B-3.MS7, shown in Figure 6B.3. Page 2 of 4 Module 3: Laboratory 2B: Shift Registers Figure 6B.3: Pseudorandom pattern generator
9. Simulate the circuit. Record the output patterns in Table 6B.1.
Pattern ABCD Pattern 0 8 1 9 2 10 3 11 4 12 5 13 6 14 7 15 ABCD Table 6B.1: Pattern generator output patterns
10. Experiment with different feedback inputs for the XNOR gate. What do you find?
Discussion: While reviewing your data and results, provide detailed answers to each of the following: Page 3 of 4 Module 3: Laboratory 2B: Shift Registers 1.
2.
3.
4. Why does the pattern in a shift register shift only one bit position each time it is clocked?
What pattern is not output by the pseudorandom pattern generator?
Which shift registers covered in this experiment require a clock pulse to load data?
Explain how to build a 20-bit shift register. Page 4 of 4 Engineering Technology