# Computer Architecture And Organization Question Paper

Computer Architecture And Organization

Course:Bachelor Of Science In Telecommunication And Information Technology

Institution: Kenyatta University question papers

Exam Year:2009

KENYATTA UNIVERSITY
UNIVERSITY EXAMINATIONS 2009/2010
FIRST SEMESTER EXAMINATION FOR THE DEGREE OF BACHELOR OF
SCIENCE IN TELECOMMUNICATION AND INFORMATION TECHNOLOGY
SPH 312: COMPUTER ARCHITECTURE AND ORGANIZATION

DATE: Wednesday 23rd December, 2009 TIME: 11.00 a.m. – 1.00 p.m.

INSTRUCTIONS
Answer question ONE and any other TWO questions. Question ONE carries 30 marks
while each of the other TWO questions carries 20 marks. The 3085 instruction set is
appended.

1.
(a)
(i)
Perform the following arithmetic

I
CDF + ABC

[2 marks]
II
00001000

00000011 [2
marks]
(ii)
Convert
(15.625)10
into
binary [2
marks]

(b)
(i)
State De Morgan’s theorem of two variables.
[2 marks]

(ii)
Obtain the output logic expression of the given logic diagram.

[3 marks]

Page 1 of 6

(iii)
Using De Morgan’s and Boolean theorem’s simplify the output
logic expression in (ii) above and draw a logic circuit for the
simplified
function.
[3
marks]
c)
(i)
What
is
a
logic
gate?
[1
mark]
(ii)
State
two
available
universal logic gates.

[2 marks]

(iii)
Show using a diagram how you can use a NAND gate to
implement an AND function and an OR function. [4 marks]
d)
(i)
What
is
a
microprocessor?
[1
mark]
(ii)
Explain the functions of the following 8085 microprocessor
components.
[3
marks]
I.
Stack
pointer
II.
Timing
and
control
III.
Program
counter
e)
(i)
What
is
memory?
[1
mark]
(ii)
State two groups of classifying memories. State one example of
each
class
of
memory.
[2
marks]
(iii)
Differentiate between algorithm and program.
[2 marks]

Q2.
a)
(i)
Draw a logic symbol for a NOR gate.

[1 mark]
(ii)
Outline the procedure that should be followed if a logic function is
to be implemented using NOR gates only.
[3 marks]
(iii)
Manipulate the given logic expression into a form which can be
implemented using only NOR gates and draw the logic diagram of
the
resulting
function.
[5
marks]
Y
=
B
A

C +

AC

+ B

b)
(i)
Design a two bit comparator circuit that will produce a logic output
1 when the two input signals are identical.
[3 marks]
(ii) Manipulate
the
logic
expression of the two bits circuit in (i) into a
form which can be implemented using NAND gates only. Draw
the circuit diagram of the manipulated function.
[3 marks]

Page 2 of 6

c)
(i)
Prepare K-map for the given Boolean function

Y = B + AC

[2 marks]

(ii)
Write down the simplest logic expression for the given K-map.

[3 marks]

Q3.
(a)
State and explain two modes of operation of 8255 PP1.
[2 marks]

(b)
Present the control word format for the 8255 PPI.
[3 marks]

(c)

(i)
A Microprocessor based system uses 8255 PPI as its I/O device. If
this system is to be used to read bit pattern at port C and output the
same to port A and B continuously and endlessly write an
assembly language program to perform this operation using
appropriate 8085 instruction set mnemonics. Take the first
memory location to be 6EFDH and use delay constant of 25510 in
register pair B.

[6 marks]

(ii)
State the memory address of the last byte of the program in (i)
above.
[1
mark]

(d)
(i)
Hand assemble the following using 8055 instruction set assuming
that the first memory location is 52EFH.

[6 marks]

Page 3 of 6

START:
LXI SP, 0F00H
LXI
H,

065DH

MVI C, 6BH
XRA
A

MOVB, A
AGAIN: CALL
DEL

INX H

DCR C
JNZ
AGAIN
LX1H,
00FFH

CALL DEL
MOV
A,
B
JMP
START
DEL:
LX1
D,
EDFFH
BACK: DCX
D
MOV
A,
E
OR
A,
D
JNZ
BACK:

RET.
(ii)
State the address of the following in the hand assemble program in
(i)
above.
[2
marks]
I.
AGAIN
label
II.
JMP
instruction

Q4.
(a)
What
is
analog
interfacing?
[1
mark]
(b)
Explain why input/output devices cannot be interfaced directly to a
microprocessor. [2
marks]
(c)
State and explain two types of interfaces.

[4 marks]
Page 4 of 6

(d)
Write an algorithm for adding odd numbers between 20 and 50 and
display (show) sum in port 01H using the 8085 instruction set. Develop

(i)
Outline the procedure followed, use registers A, B and C.

[4 marks]
(ii)
Assuming that the first memory location is 25EEH, write an
assembly language program to perform this operation using
appropriate 8085 mnemonics. Show also the memory contents in
hex
codes.
[6
marks]
(iii)
Simplify your program in (ii) using a flow chart.
[3 marks]

Q5.
(a)
State and explain the functions of the four fields of assembly language
program.

[4 marks]

(b)
State and explain three classifications of 8085 instruction sizes.

[3 marks]
(c)
Write a program of subtracting two numbers; 58H from 82H using 8085
assembly language and display the results in part 02H.
[3 marks]

(d)
Consider the following 8085 assembly language program of a
microprocessor-based system using 8255 PPI.

MV1A, 80H

OUT
03H

BACK:
MVI A,
55H

OUT
00H

OUT
01H

OUT
02H

CALL
SUBRONTINE

MVIA,
AAH

OUT
00H

OUT
01H