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]?
1
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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