CSc 343
Computer Organization and Programming
Spring Quarter 1998
Solutions to Mid-Term Exam (4 May 1998, Monday)
1. Convert the number -117.375 to IEEE single-precision floating point format.
Give your answer in HEX.
C2EAC000
2. What does the following IEEE single-precision floating point
number represent?
FF800000
-infinity
3. Assume that AX = BBBBh and BX = BBBBh. What will be the contents
of the AX register after the instruction:
ADD AL,BL
is executed.
A. BBBBh B. BBF6h C. BB76h D. BB78h E. None of these
Answer: C
What will the condition code bits be after the instruction is
executed.
A. SF=0 ZF=0 OF=0 CF=1 B. SF=0 ZF=0 OF=1 CF=1
C. SF=0 ZF=1 OF=0 CF=1 D. SF=1 ZF=0 OF=1 CF=1 E. None of the above
Answer: B
4. Assume that AX = 11BBh and BX = 44BBh. What will be the contents
of the AX register after the instruction:
SUB AH,BH
is executed.
A. 81BBh B. CFBBh C. C1BBh D. CDBBh E. None of those
Answer: D
What will the condition code bits be after the instruction is
executed.
A. SF=1 ZF=0 OF=0 CF=1 B. SF=1 ZF=0 OF=1 CF=1
C. SF=0 ZF=0 OF=0 CF=1 D. SF=1 ZF=0 OF=1 CF=0 E. None of the above
Answer: E
5. Convert the address EE11:EE22 to a 20-bit address, where EE11 is the
contents of the segment register and EE22 is the offset within the
segment. Express the answer in HEX notation.
FCF32
6. Convert the 20-bit address 00100H to segment:offset notation.
Express the segment and offset as 4-digit HEX numbers.
0001:0010
7. What is the SOURCE ADDRESSING MODE for the instruction: ADD AX,[1000]
A. Register Direct B. Immediate C. Memory Direct
D. Register Indirect E. It can not be determined
Answer: C
8. What is the DESTINATION ADDRESSING MODE for the instruction: ADD AX,[1000]
A. Register Direct B. Immediate C. Memory Direct
D. Register Indirect E. It can not be determined
Answer: A
9. Given these data declaration and instructions and initial hex
value of AX=1234 then what is in AX after the last instruction
completes execution.
LIST DW 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
MOV SI,OFFSET LIST
ADD SI,6
MOV AL,[SI]
A. 1203 B. 1204 C. 1205 D. 1200 E. None of the above
Answer: A
10. Given these data declaration and instructions and initial hex
value of AX=1234 then what is in AX after the last instruction
completes execution.
LIST DW 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
MOV SI,OFFSET LIST
ADD SI,10
MOV AX,[SI]
A. 1205 B. 0005 C. 0500 D. 0050 E. None of the above
Answer: B
11. Given the following data declarations and instructions, how
many characters will be written to the standard output stream
(display or file).
MSG0 DB `HELLO'
MSG1 DB `VAL='
VALUE DB 36D
FIN DB 13,10,`$'
MSG2 DB `DONE',`$'
MOV DX,OFFSET MSG0
MOV AH,9
INT 21H
A. 0 (decimal)
B. 9 (decimal)
C. 11 (decimal)
D. 12 (decimal)
E. The number of characters can not be determined
Answer: B
Questions 12-15 refer to the following code:
MOV AX,0
MOV CX,10
REPEAT: INC AX
SUB CX,1
XXX REPEAT
DONE:
12. If the conditional jump (XXX) is replaced by JNE then what
hex value will be in AX when the loop terminates (we reach the
instruction DONE:)
A. 0000 B. 0001 C. 000A D. 000B E. None of the above
Answer: C
13. If the conditional jump (XXX) is replaced by LOOP then what
hex value will be in AX when the loop terminates (we reach the
instruction DONE:)
A. 0004 B. 0005 C. 000A D. 000B E. None of the above
Answer: B
14. If the conditional jump (XXX) is replaced by JLE then what hex
value will be in AX when the loop terminates (we reach the
instruction DONE:)
A. 0000 B. 0001 C. 000A D. 000B E. None of the above
Answer: B
15. If the conditional jump (XXX) is replaced by JGE then what
hex value will be in AX when the loop terminates (we reach the
instruction DONE:)
A. 0000 B. 0001 C. 000A D. 000B E. None of the above
Answer: D
16. The following instructions use indirect addressing to point
to data that is moved to the AX register. Which of these
instructions refers to data from the Stack Segment that
is moved to AX.
A. MOV AX,[SI]
B. MOV AX,[DI]
C. MOV AX,[BX]
D. MOV AX,[BP]
E. None of the above
Answer: D
17. Write a single instruction that clears (sets to 0) the AX register.
Do not use the SUB or the MOV instruction.
XOR AX,AX
18. Name the instruction that could be used to test the bit that was
``shifted off'' during a shift operation.
JC
19. Suppose that AL contains 93H and BL contains 44H. What is the outcome of
the following instructions?
CMP AL,BL
JE A10 Jumps_______ Does not jump__X____
CMP AL,BL
JNZ A10 Jumps___X___ Does not jump_______
CMP AL,BL
JAE A10 Jumps___X___ Does not jump_______
CMP AL,BL
JL A10 Jumps___X___ Does not jump_______
CMP AL,BL
JB A10 Jumps_______ Does not jump__X____
20. List the bytes that would be generated by each of the
following directives. Show byte values in HEX; Write one
byte per line. (You may not need all the lines provided).
Show bytes in the order they will appear in memory.
DB 'Foo','bar' _46_ _6F_ _6F_ _62_ _61_ _72_ ____ ____ ____ ____
DB -128 _80_ ____ ____ ____ ____ ____ ____ ____ ____ ____
DW 0FFFFH,-1 _FF_ _FF_ _FF_ _FF_ ____ ____ ____ ____ ____ ____
DW 4 DUP (1023) _FF_ _03_ _FF_ _03_ _FF_ _03_ _FF_ _03_ ____ ____
21. Write a short program segment that multiplies AL by 12
using shift, move, and add instructions.
mov bl,al
mov cl,3
shl al,cl
mov cl,2
shl bl,cl
add al,bl
22. What will be the contents of AX register after the following
instructions execute?
MOV AX,63h
MOV BL,10h
DIV BL
AX = 0306
23. The following assembler instructions have been partially
translated to machine code. Finish the translation by
filling in the missing words.
Offset Machine Code Source Code
______ _____________ __________________________
0000 .model small
0000 .stack 32
0000 .data
0000 .code
0000 proc1 proc near
0000 E8 0004 call proc2
----
0003 05 0001 add ax,1
0006 C3 ret
0007 proc1 endp
0007 proc2 proc near
0007 03 C0 add ax,ax
0009 C3 ret
000A proc2 endp
000A main proc far
000A B8 0001 mov ax,1
000D E8 FFF0 call proc1
----
0010 E8 FFF4 call proc2
----
0013 B4 4C mov ah,4cH
0015 CD 21 int 21h
0017 main endp
end main
24. What will be the contents of AL after each of the following
instructions is executed? Assume that AL = EAh, CL = 2, and
the Carry Flag is 0 before each instruction is executed.
SHL AL,1 AL = D4
SHL AL,CL AL = A8
ROL AL,CL AL = AB
RCR AL,CL AL = 3A
SAR AL,1 AL = F5
25. Write a procedure that will exchange the high and low halves of
the DL register. Make sure that you push and pop any other registers
you will use in the procedure. Also, DH should remain
unaltered after the procedure is completed.
(Hint: Use the logical operations AND/OR with a mask)
exchangedl proc near
ror dl
ror dl
ror dl
ror dl
exchangedl endp