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Lab 4

Lab 4. Logic Instructions, Shift Instructions and Rotate Instructions. Logic Instructions. AND destination, source Can be used to clear(0) specific destination. Ex: b AND 1 = b b AND 0 = 0 OR destination, source Can be used to set(1) specific destination. Ex: b OR 0 = b b OR 1 = 1

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Lab 4

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  1. Lab 4 Logic Instructions, Shift Instructions and Rotate Instructions

  2. Logic Instructions • AND destination, source Can be used to clear(0) specific destination. Ex: b AND 1 = b b AND 0 = 0 • OR destination, source Can be used to set(1) specific destination. Ex: b OR 0 = b b OR 1 = 1 • XOR destination, source Can be used to complement(opposite) specific destination. Ex: b XOR 0 = b b XOR 1 = ~b

  3. Cont. Logic Instructions • NOT destination Performs one’s complement (opposite) on destination. • TEST destination, source Performs AND operation but does not change the destination contents.

  4. Example 1 • Enter an ascii digit, convert it to a number then display the ascii of it in a new line. org 100h MOV AH, 1 INT 21H ;a function to input a ascii number from user AND AL,0FH ;converting to a number MOV BL,AL MOV AH,9 LEA DX,NEWL INT 21H ;printing a newline MOV AH,2 MOV DL,BL INT 21H ;printing the converted number in ascii code ret NEWL DB 0DH,0AH,"$"

  5. Example 2 • MOV number 5 in BL register and display it as an output. org 100h MOV BL,5 ;assign 5 to BL OR BL,30H ;convert it to an ascii character ;so it can be printed as 5 MOV AH,2 MOV DL,BL INT 21H ;print the number ret

  6. Clearing • Clear AX MOV AX, 0 or SUB AX, AX or XOR AX,AX • Clear MEM • MOV MEM,0

  7. Shift Instructions • SHL destination, numberOfShifts • Shifts the bits in destination to the left. • numberOfShifts must be a direct value or a value in CL register. • Inserts 0 to the rightmost bit. • Loses the leftmost bit and adds to CF. • Every left shift is a multiplication by 2 • SHR destination, numberOfShifts • Shifts the bits in destination to the right. • numberOfShifts must be a direct value or a value in CL register. • Inserts 0 to the leftmost bit. • Loses the rightmost bit and adds to CF. • Every right shift is a division by 2

  8. Example 3 • Multiply 8 by 8 and divide 65 by 4. org 100h MOV BL,8 MOV CL,3 SHL BL,CL MOV BH,65 MOV CL,2 SHR BH,CL ret

  9. Rotate Instructions • ROL destination, numberOfRotations • Shifts the bits in destination to the left. • numberOfShifts must be a direct value or a value in CL register. • The leftmost bit is inserted in the rightmost bit. • Adds to CF. • ROR destination, numberOfRotations • Shifts the bits in destination to the right. • numberOfShifts must be a direct value or a value in CL register. • The rightmost bit is inserted in the leftmost bit. • Adds to CF.

  10. Example 4 • Assign 55 to BX register then count the number of 1 bits and display it on screen. org 100h MOV BX,55 XOR DX, DX ; AX counts bits MOV CX, 16 ; loop counter TOP: ROL BX, 1 ; CF = bit rotated out JNC NEXT ; 0 bit INC DX ; 1bit, increment total NEXT: LOOP TOP ; loop until done OR DX,30H MOV AH,2 INT 21H ret

  11. Example 5 • Input a binary number then display it in a newline. org 100h XOR BX,BX ; CLEAR BX MOV AH,1 INT 21H ; Input character WHILE_: CMP AL, 0DH ; CR? JE END_WHILE ; YES, DONE AND AL, 0FH ; CONVERT TO BINARY VALUE SHL BX,1 ; MAKE ROOM FOR NEW VALUE OR BL,AL ; PUT VALUE IN BX INT 21H ; READ A CHARACTER JMP WHILE_ ; LOOP BACK END_WHILE:

  12. Cont. Example 5 mov ah,9 lea dx,newl int 21h MOV CX,16 MOV AH,2 TOP_: ROL BX,1 ;content in BX JC display_one ; print bit ‘1’ MOV DL,"0" ; else Print bit ‘0’ JMP display display_one: MOV DL,"1" Display: INT 21H ; Print bit either ‘0’ or ‘1’ LOOP TOP_ ; LOOP BACK ret newldb 0ah,0dh,"$"

  13. Exercise 1 • Let the user enter 2 numbers 4 and 5 then display the sum of them. • org 100h • ;prepare to read first number • MOV AH,1 • INT 21H • ;save the number in other register • MOV BL,AL • ;convert the number to its decimal value • AND BL,0FH • ;display addition symbol • MOV AH,2 • MOV DL,2BH • INT 21H • ;prepare to read second number • MOV AH,1 • INT 21H • ;convert the number to its decimal value • AND AL,0FH

  14. Cont. Solution • ;add the two numbers • ADD BL,AL • ;convert the number so it would be printed as its symbol • OR BL,30H • ;display a newline that is saved in a variable • MOV AH,9 • LEA DX,NWL • INT 21H • ;display the result • MOV AH,2 • MOV DL,BL • INT 21H • ret • NWL DB 0DH,0AH,"$"

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