Microprocessors / DEBUG Lab Calculation and Comparisons
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lab_04.docThe Intel Family of Microprocessors
James L. Antonakos
Lab #4: Calculations and Comparisons
Reference: Chapter 4
Introduction
The purpose of this experiment is to see how typical mathematical calculations, as well as numeric and logical comparisons, are performed.
Procedure
1. The sun is 93,000,000 miles from the Earth. The speed of light is 186,000 miles/second. How long does it take a ray of light to reach the Earth? The correct answer is 8 minutes, 20 seconds. Enter and save the file SUN.SCR:
2. Open a DOS window, and enter the following DEBUG command:
DEBUG < SUN.SCR
What is the final value in the AX register? Does it represent some combination of 8 and 20? Hint: Remember that DEBUG only works with hexadecimal numbers.
3. Explain how the calculations were performed in SUN.SCR. For example, were the numbers 93,000,000 and 186,000 represented anywhere? If not, why not?
4. Enter and save the file AVG.SCR and process it using DEBUG. What is the final value in AL? Explain why the value is correct.
5. Enter and save the file CMPUNSGN.SCR. Then open a DOS window and enter the following command:
DEBUG < CMPUNSGN.SCR
Discuss the relationship between the instructions and the results indicated by the flags. Hint: See Example 4.7.
6. Repeat step 5 using the file CMPSIGN.SCR:
7. Enter and save the source file COMPARES.ASM. Assemble, link, and run. Examine the results.
;Program COMPARES.ASM: Compare two words of data different ways.
;
.MODEL SMALL
.DATA
NUM1 DW 25000
NUM2 DW 26000
AXMSG DB 'AX equals$'
BXMSG DB 'BX equals$'
MSG DB ' '
TENTHOS DB ?
THOUS DB ?
HUNS DB ?
TENS DB ?
ONES DB ?
DB 0DH,0AH,'$'
IMSG DB 'Instruction: CMP AX,BX',13,10,'$'
JCTMSG DB 'JC is True',13,10,'$'
JCFMSG DB 'JC is False',13,10,'$'
JZTMSG DB 'JZ is True',13,10,'$'
JZFMSG DB 'JZ is False',13,10,'$'
JATMSG DB 'JA is True',13,10,'$'
JAFMSG DB 'JA is False',13,10,'$'
JLTMSG DB 'JL is True',13,10,'$'
JLFMSG DB 'JL is False',13,10,'$'
.CODE
.STARTUP
LEA DX,AXMSG ;display AX value
MOV AH,9
INT 21H
MOV AX,NUM1
CALL BTOD
LEA DX,MSG
MOV AH,9
INT 21H
LEA DX,BXMSG ;display BX value
MOV AH,9
INT 21H
MOV AX,NUM2
CALL BTOD
LEA DX,MSG
MOV AH,9
INT 21H
LEA DX,IMSG ;show 'CMP AX,BX'
MOV AH,9
INT 21H
MOV AX,NUM1 ;start the comparisons
MOV BX,NUM2
CALL DOJC
MOV AX,NUM1
MOV BX,NUM2
CALL DOJZ
MOV AX,NUM1
MOV BX,NUM2
CALL DOJA
MOV AX,NUM1
MOV BX,NUM2
CALL DOJL
.EXIT
DOJC PROC FAR
CMP AX,BX
JC JCOK
LEA DX,JCFMSG
MOV AH,9
INT 21H
RET
JCOK: LEA DX,JCTMSG
MOV AH,9
INT 21H
RET
DOJC ENDP
DOJZ PROC FAR
CMP AX,BX
JZ JZOK
LEA DX,JZFMSG
MOV AH,9
INT 21H
RET
JZOK: LEA DX,JZTMSG
MOV AH,9
INT 21H
RET
DOJZ ENDP
DOJA PROC FAR
CMP AX,BX
JA JAOK
LEA DX,JAFMSG
MOV AH,9
INT 21H
RET
JAOK: LEA DX,JATMSG
MOV AH,9
INT 21H
RET
DOJA ENDP
DOJL PROC FAR
CMP AX,BX
JL JLOK
LEA DX,JLFMSG
MOV AH,9
INT 21H
RET
JLOK: LEA DX,JLTMSG
MOV AH,9
INT 21H
RET
DOJL ENDP
BTOD PROC FAR
SUB DX,DX
MOV BX,10000
DIV BX ;get 10,000s digit
ADD AL,30H
MOV TENTHOS,AL
XCHG AX,DX
SUB DX,DX
MOV BX,1000 ;get 1,000s digit
DIV BX
ADD AL,30H
MOV THOUS,AL
XCHG DX,AX
MOV BL,100
DIV BL ;get hundreds digit
ADD AL,30H ;convert into ASCII digit
MOV HUNS,AL ;and save
XCHG AL,AH ;get remainder
SUB AH,AH ;prepare for division by 10
MOV BL,10
DIV BL ;get tens digit
ADD AL,30H ;convert into ASCII digit
MOV TENS,AL ;and save
ADD AH,30H ;convert ones digit into ASCII
MOV ONES,AH ;and save
RET
BTOD ENDP
END
8. Choose four additional types of conditional jump instructions and add the appropriate procedures to test the new jump instructions. Your final program will show the results of eight comparisons. Include the list file with your writeup.
9. Write a one-page summary of what you learned during the laboratory.
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