Homework 7

Max marks: 60

Problem 1 Consider the timing diagram in

Figure 1. Assuming that the D and Clock inputs shown are applied to the circuit in Figure 2,

draw waveforms for the Qa , Qb , and Qc signals.

(10 marks) [1, Prob 5.1]

Figure 1: Inputs for Prob 1

Figure 2: Circuit for Prob 1. Recall that Clk

with a “.” symbol indicates rising-edge (positiveedge) triggered flip-flop. Clk without “.” symbol

indicates a level-triggered latch. Clk with “◦.”

symbol indicates a falling-edge (negative-edge)

triggered flip-flop.

Problem 2 Figure 3 shows a S-R latch built

with NOR gates. Draw a similar latch using

NAND gates. Derive its characteristic table and

show its timing diagram. Assume that S¯ and R¯

are available. (10 marks) [1, Prob 5.2].

Figure 3: Circuit for Prob 2

Problem 3 An SR flip-flop is a flip-flop that

has set and reset inputs like a gated SR latch.

Show how an SR flip-flop can be constructed

using a D flip-flop and other logic gates. (10

marks) [1, Prob 5.5]

Problem 4 Show how a JK flip-flop can be constructed using a T flip-flop and other logic gates

(10 marks) [1, Prob 5.7].

Problem 5 Design a three-bit up/down counter

using T flip-flops. It should include a control

input called Up/Down. If Up/Down = 0, then

the circuit should behave as an up-counter. If

Up/Down = 1, then the circuit should behave as

a down-counter. You can use a 2-1 MUX for the

switching or you can uses basic logic gates (10

marks) [1, Prob 5.15].

Problem 6 The circuit in Figure 4 looks like a

counter. What is the counting sequence of this

circuit (10 marks) [1, Prob 5.17]?

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Figure 4: Circuit for Problem 6.

References

[1] S. Brown and Z. Vranesic. Fundamentals of

Digital Logic with Verilog Design: Third Edition. McGraw-Hill Higher Education, 2013.

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