University of Waterloo
Department of Electrical and Computer Engineering
ECE 223 Digital Circuits and Systems
Final Examination
Winter 2000
Duration 3 hours Instructor: M. Sachdev Date April 12, 2000
Name .......................................................... Student ID ..........................................
1 2 3 4 5 6 7 8 9 Total
Notes
1. Attempt all problems.
2. If information appears to be missing make a reasonable assumption, state it and proceed.
3. Calculators are not needed and are not allowed.
4. No additional material is allowed.
Name:.................................................... Student id:.....................................................
Problem 1
(A): Convert following number from one radix to another [4]
(127.094)10 to radix 5
(B): Write a 4-bit gray code. In what applications usage of gray code is desirable? [4]
Name:.................................................... Student id:.....................................................
Problem 2
(A): What is the difference between Mealy and Moore machines [4]
(B): Highlight two major differences between a Programmable Logic Array (PLA) and a Programmable
Array Logic (PAL) devices [4]
Name:.................................................... Student id:.....................................................
Problem 3
Simplify the following Boolean function by means of Quine-McCluskey tabulation method [12]
P(A,B,C,D,E,F) = Σ ( 6, 9, 13, 18, 19, 25, 27, 29, 41, 45, 57, 61 )
Name:.................................................... Student id:.....................................................
Problem 4
Design a combinational circuit that converts a binary number of 4 bits (WXYZ) to a binary coded decimal
(BCD) format. Show the logic level implementation. [12]
Name:.................................................... Student id:.....................................................
Problem 5
Give a logic diagram of a level sensitive, master-slave flip-flop. Why edge triggered flip-flops are gener-
ally preferred in digital designs? Give a logic level diagram for an edge triggered flip-flop. [12]
Name:.................................................... Student id:.....................................................
Problem 6
A sequential circuit is shown in the figure. Derive the state table and state diagram of the circuit [12]
J Q A J Q B
B’
K Q’ K Q’
CP
y
x
Name:.................................................... Student id:.....................................................
Problem 7
Design a 4-bit ripple counter with Toggle flip-flops. What is the disadvantage of a ripple counter? [12]
Name:.................................................... Student id:.....................................................
Problem 8
Construct an ASM chart for a digital system that counts the number of people in a room. People enter the
room from one door with a photocell that changes a signal x from 1 to 0 when the light is interrupted. They
leave the room from a second door with a similar photocell with a signal y. Both x and y are synchronized
with the clock but may stay on or off for more than one clock pulse period. The data processor subsystem
consists of an up-down counter with a display of its contents. [12]
Name:.................................................... Student id:.....................................................
Problem 9
Derive the transition table for the asynchronous sequential circuit shown in the figure. Determine the
sequence on internal states Y1Y2 for the following sequence of inputs, x1x2 : 00, 10, 11, 01, 11, 10, 00 [12]
x
1
Y
1
x2
Y
2
