# 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

your program as follows:

(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

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

your program as follows:

(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