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Instructor: Dr Konstantinos Katzis
Tel: 22-713296
e-mail: [email protected]
Fall Semester 2009
80x86
Assembly Language
Revision Exercises
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1) What is the function of the CPU the instruction set? List 3 CPU components and
briefly describe Machine Cycle.
2) Example: Suppose that EAX= 00002000h, EBX=00001000h, ESI=00002000h, EDI
=00003000h and the memory locations 00001000h, 00002000h, 00003000h contain the
values 00001BACh, 000020FEh and 0000031Dh respectively. For each of the following
instruction write down the contents of the memory and the registers EBX,ECX,ESI,EDI.
EBX
EXC
ESI
EDI
0000
1000h
?
0000
2000h
0000
3000h
0000
1000h
0000
1BACh
0000
2000h
0000
3000h
0000
20FEh
0000
031Dh
mov EBX,[EBX]
mov ECX,[ESI]
mov EBX,[EAX]
add [ESI],[EDI]
inc EDI
inc [ESI]
3) Fill in the following registers
Address
000010F0
000010F1
000010F2
000010F3
000010F4
000010F5
000010F6
000010F7
mov ESI,000010F2h
mov AH,[ESI]
inc ESI
mov AH,[ESI]
add ESI,4
mov AH,[ESI]
mov AX,ESI
Memory Contents
1Ch
F3h
5Ah
19h
67h
42h
23h
45h
; AH now contains 5Ah
; ESI now contains __________
; AH now contains __________
; ESI now contains __________
; AH now contains __________
; AX now contains ___________
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4) Write code to define two arrays. The first one should be an array of bytes contain the
values A0h, 2Ah, 0Dh and F0h. The second one should contain 3 un- initialized double
words. Use a table to show the memory contents after the declarations.
5) Show how the following items will be stored in memory
var1 BYTE 00001111b
var2 BYTE 10
var3 BYTE “hello”
var4 WORD 20
var5 DWORD 20
var6 BYTE –3
var7 WORD 2, 5h, 3, 001b
6) Answer the following questions related to the code listed below.
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6a) Number1,number2 are double words. Number1 and Number 2 are saved in in
memory locations 00000000 and 00000004. Why?
6b) Prompt1 starts at memory location _ _ _ _ _ _ _ _ and prompt2 start at memory
location 0000001E
6c) Draw a table showing the contents of the memory after the declarations show in the
data segment of exercise 6.
Address
Contents
Address
Contents
Address
Contents
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7) Write a program in assembly to add three numbers input by the user, and output the
result.
8) Explain the actions taking place in each of the following operations. Indicate any
illegal operations
.data
b1 BYTE 4Fh
b2 BYTE 3Ah
w WORD 2048
.code
mov bl,dh
mov ax,w
mov ch,b1
mov b2, b1
mov al,255
mov al, w
mov w,-100
mov b,0
9) Fill in the following comments:
Examples:
.data
b
w
ww
BYTE 03
;____________
WORD
08
;____________
DWORD 12 ; _ _ _ _ _ _ _ _ _ _ _ _
.code
mov ax, 05
add ax, w
mov bl, 23
add w, bl
mov EAX, 0
add EAX, ww
;____________
;____________
;____________
;____________
;____________
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10) Fill in the flag status:
11) Write code to calculate the expression:
res=-2*(num1+num2-num3) +1
(Note: res, num1, num2 and num3 are WORDS stored in memory).
12) Describe the use of the following directives - part of an assembly code:
a. .386
b. .MODEL FLAT
c. .DATA
13) Fill in the following:
Before
AX: 00 05
BX: 00 02
DX: ?? ??
Instruction Executed
imul bx
After
DX: __ __
AX: __ __
CF, OF: __
AX: ?? 05
Factor = FF
imul Factor
AX: __ __
CF, OF: __
EBX: 00 00 00 0A
imul ebx,2
EBX : __ __ __ __
CF, OF: __
ECX: FF FF FF F4 imul ecx,Factor
Factor=FF FF FF F2
ECX : __ __ __ __
CF, OF: __
Value= 00 F2 (242d) imul bx,Value, 2
BX: ?? ??
BX : 01 E4
CF, OF: __
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14) Write a program that calculates 1+2+3+4+5+6. . .
The result (sum is saved in memory in a location shown by the label SUM)
15) Write the output of the following programs. (assume that the user inputs the numbers
3, 5 and 4 when requested)
.DATA
sum
prompt
number
countLabel
sumLabel
avgLabel
value
nextPrompt
.CODE
_start:
forever:
; reserve storage for data
DWORD ?
BYTE "number? ",0
BYTE 16 DUP (?)
BYTE "count",0
BYTE "
sum",0
BYTE "
average",0
BYTE 11 DUP (?), 0
BYTE cr,Lf,Lf,"next ",0
; start of main program code
mov sum,0
mov ebx,0
; sum := 0
; count := 0
output prompt
input number,16
atod number
add sum,eax
inc ebx
; prompt for number
; read ASCII characters
; convert to integer
; add number to sum
; add 1 to count
dtoa value,ebx
output countLabel
output value
; convert count to ASCII
; display label for count
; display count
dtoa value,sum
output sumLabel
output value
mov eax,sum
cdq
idiv ebx
dtoa value,eax
output avgLabel
output value
; convert sum to ASCII
; display label for sum
; display sum
; get sum
; extend sum to 64 bits
; sum / count
; convert average to ASCII
; display label for average
; output average
output nextPrompt
jmp forever
PUBLIC _start
END
; skip down, start next prompt
; repeat
; make entry point public
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16) Write down the values of the ZF, CF and SF after each of the following instructions
is executed. Indicate any illegal instructions
.data
num1 BYTE 30h
num2 BYTE FFh
.code
ZF
CF
SF
mov ah, 31h
;
cmp ah, num1 ;
cmp ah, 31h
;
cmp num2, F0h
;
cmp 40h, ah
;
cmp ah, ‘A’
;
17) Write code to add 50 to the current value of the ax register. If the result of the
addition is positive set in the bx register the value 1. If the result of the addition is
negative set in the bx register the value -1.
18) Write a program to compare the values in the AX and BX registers, and set the
biggest value (among the two) in the CX register.)
19) Write assembly language code for the following statements, using Conditional
JUMPS
a=5
for i=0: until i=50 do
a:=a+1
end
20) Write code to for performing the following actions:
If AX < 0
then
Set the number 5h in the BX register
Else
Set the number 22h in the BX register
21) Write code to calculate the sum of the following series:
1 + 4 + 7 + 10 + . . . ., until the sum becomes greater than 100.
22) Write code for the following statements
if (value >=30) or (value<10)
then
value = 100
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23) Write code for the following statements
if (value >=30) AND (rate>10)
then
value = value-1
24) Describe in words the functionality of the following program.
mov
mov
ADD_ONE: add
add
mov
loop
AX,00h
ECX 20d
AX,01h
BX,01h
ECX, 05h
ADD_ONE
; reset AX
; set counter to 20
; repeated 20 times
25) Write code to define two arrays of double words of 50 elements each. Also write
code to copy the contents of the first array to the contents of the second array.
26) Write code to define an array of double words with the following items.
f304, 00f5, 143d, c4f2. Also write code to calculate the sum of all array items and store
the result in a variable called SUM.
27) Initially BX=6DA4, EAX=FD347CCC and ESP=000F1007. Show the contents of the
stack and the ESP after the following instructions are executed.
push BX
push EAX
Address
000F1008h
000F1007h
000F1006h
000F1005h
000F1004h
000F1003h
000F1002h
000F1001h
000F1000h
000F1008h
Contents
23h
FDh
ESP=000F1007h
28) Let ESP=000F1000. Show the contents of the ax and ebx registers when the
following instructions are executed
pop AX
pop EBX
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Address
000F1008h
000F1007h
000F1006h
000F1005h
000F1004h
000F1003h
000F1002h
000F1001h
000F1000h
Contents
23h
FDh
43h
F5h
Dah
AAh
6Dh
65h
09h
29) Write a procedure called swap that accepts the address of two words in the stack and
swaps their values
30) Write code to move 20 bytes from STRING1 to STRING2 without using string
operations.
31) Write a program to check whether a 10 character password entered by a user is the
same with a pre-stored 10 character password. Assume that the pre-stored and entered
passwords are already available in memory with the names passw and str.
32) Write a procedure that accepts a word in the AX register and returns in the EBX
register the number of one’s in the word given.
33) Fill in the following:
mov
mov
sal
sar
AH,01101101b
CL,2
AH,1
AH,CL
; AH now contains ____________
; AH now contains ____________
;AH now contains ____________
; AH now contains ____________
34) Fill in the following:
mov
mov
rol
ror
AH,01101101b
CL,2
AH,1
AH,CL
; AH now contains ____________
; AH now contains ____________
;AH now contains ____________
; AH now contains ____________
35) Write a procedure to output on the screen the contents of the AH register in binary
format. (Hint convert the contents of AH into an 8 byte string containing ‘0’ or ‘1’
characters.
36) What is RISC and CISC. List their advantages and disadvantages and compare the
two.
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37) List three advantages and three disadvantages of assembly.
38) Find the word-length 2’s complement representation of each of the following
DECIMAL numbers:
845, 15000, -923
39) Perform each of the following operations on word-size 2’s complement numbers. For
each, find the specified sum or difference. Determine whether overflow occurs.
Depending on the operation, determine whether there is a carry or a borrow. Repeat the
following operations in decimal.
a. 8E3D + C3A9
b. 00C3 – 026A
c. E9FF + 8CF0
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