=========================preview======================
(ELEC151)[2009](f)midterm~cs_fmh^_10279.pdf
Back to ELEC151 Login to download
======================================================
Name: Student J.D. Number: _
ELEC 151: Digital Circuits and Systems
(Fall 2009)
Mid-term Examination
Date: 30/10/2009 (Friday)
Time: 7:00 -8:30 p.m.

1.
There are~questions in this examination. Answer all questions in this question booklet.

2.
Write down your name and student 10 number in this page and put your student 10# at the upper left comer of each page in this booklet.

3.
Answer all the questions in the space provided.


Question Number Total Marks Score
1 8
2 26
3 20
4 26
5 20
Total 100

1. (8 marks) True and False Questions
a. (1 mark) A4-to-l mux has 4 inputs and 1 output.
-c
Answer: L_
b. (l mark) An even parity bit checker can detect even number of bit error.
Answer: r
c. (1 mark) We can just use only 2-input NAND gate to implement any combinational
Boolean function. Answer: l: _
d. (1mark) Ifx=10010,Y= 10110andz= x+y=11000,thenx,yandzarerepresented using signed magnitude format.
Answer: -r
e. (1 mark) When the enable input to the tri-state buffer equals to zero, the output of the tri-state buffer is O.
Answer: T"--_
f. (1 mark) Ifx, y and z are three consecutive numbers represented in Gray code, x and z are different in only 2 bit locations.
Answer: T_
g. (1 mark) One ofthe advantages of using 2s complement number is that an adder can be used to execute both addition and subtraction oftwo numbers.
Answer:
T----
h. (1 mark) The following is a transmission gate because the pmos transistor and nmos transistor are both turned on when signal S is 1 and they are both turned off when signal S is O.
Answer: F_-_ 2) Short question (26 marks)
a) (4 marks) The following are two 6-bit 2's complement numbers: 101010, 110100. Add them
up and detennine whether there will be overflow problem.

10/0 10

+ I I 0 I 00
I 0 II 110

1

~ral. ~ M<6B c~~~ ~ 0 to I) w~~ ~ "t~4t 9. ~
1'\J.n\\m.. o.dd ~1kt ~ 0. f~itW. nVI7lb?r , o~.fh.J O..\Jr
b) (2 marks) For a decoder that has 8 inputs, how many outputs does it have?
c) (4 marks) List the range of number (in decimal) that can be represented by i) a 16-bit unsigned number
o -7 }/b_ \
::: 0 ~ 6553S-
ii) a 16-bit 2's complement number
15' 15
-2 ~ 2-1
-t>11b8 ~ ;))=tbt

d) (4 marks) Given the following K-map, write down the function F in minimum product-of-sum form.

F= ~D+f\c.+~D1BC-
=-(7\0)( AC )(BD)( Be. ) :: (AtD)(f\\-c:) (B-tD)(B+c)
e) (2 marks) A 5-input XOR gate has 5 inputs (A,B,C,D,E) and 1 output (Out). What is the value of Out when ABCDE =01011?
AIDB@c E9 D$ E
::.o@I~O&/~1
-:: I
f) (2 marks) Show how to implement an inverter using a 2-input NAND gate.
AVB
g) (2 marks) Show how to implement a 2-input NOR gate using 2input NAND gates and inverters.
::.
c

h) (6 marks) Use 2-input NAND gate only to implement the following circuit. a =='"'T"==!'o..
b ..,.,....",..,.,....",.,-,1
C "=""".,.",..,.,.-"t

:~'"""""',.~................. ....
......