1. Microprocessor and Assembly Language
Lecture-9-Bit Manipulation Instructions
Muhammad Hafeez
Department of Computer Science
GC University Lahore

2. Today’s Agenda Logic Instructions (AND, OR, NOT, XOR)
Shift Instructions (SHL, SHR, SAL, SAR)
Rotate Instructions (ROL, ROR, RCL, RCR)

3. Login Instructions
Usage
To Set Bits
To Clear Bits
To Examine Bits

4. AND, OR, XOR
Peform Bit-Wise Operations on Operands and store result in destination
Sytax
AND Destination, Source
OR Destination, Source
XOR Destination, Source
Destination Must be Register or Memory Location
Source could be immediate, register or memory location
Memory to Memory is not allowed

5. AND, OR, XOR Affect On Flag Rgister
SF, ZF, SF are affected
AF is undefined
CF, OF=0 (since they operate on bits not on numbers)

6. Bit Manipulation Using Mask
We can selectively modify bits in Destination using bitter pattern called ‘mask’
We use following properties of AND, OR and XOR
Y AND 1 = Y, Y AND 0 = 0
Y OR 1 = 1, Y OR 0 =Y
Y XOR 1 = ~Y, Y XOR 0 = 1

7. Bit Encoding and Use of Bit Masks
ASCII is a bit encoding of English Character Set, you can develop encoding at your own
AND can be used to clear bits, prepare a bit pattern (mask) that has a ‘0’ at particular bit position, set ‘1’ at remaining position to preserve them
OR can be used to set bits, prepare a mask that has ‘1’ at particular bit, position, place ‘0’ at other position
XOR can be used to complement specific bit, a ‘1’ mask complement, ‘0’ preserve

8. Examples Prepare following Masks:
Clear the Sign of AL=0E5H using AND Instruction
Set MSB and LSB and clear other bits in BL=0DFH using OR
Change Sign of DL=0FEH using XOR

9. Use in Assembly Language
AND Instruction is used
Convert an ASCII Digit to a Number (Its Reverse)
Convert an Upper Case Letter to Lower Case (Its Reverse)

10. Use in Assembly Language
AND Instruction is used
Convert an ASCII Digit to a Number
Bit mask – b – Hex = 0FH
AND this mask with Destination (Reg/ Mem)
AND AL,0FH
(Its Reverse)
Convert an Upper Case Letter to Lower Case
Bit Mask = d – Clear 5th Bit
AND AL, 0DFH (Its Reverse)

11. Use in Assembly Language
XOR Instruction is used
Clear a Register/ Memory Location
Alternate is MOV AX,0
Or XOR AX,AX
In what condition XOR cannot be used? (m/m)
OR Instruction
OR AL, AL = CMP AL,0
Test a register is zero

12. Use in Assembly Language
NOT Instruction is used
To compliments the bits

13. Test Instruction
Just Like CMP to SUB instruction, TEST instruction is the alternate to AND instruction
Used to Test specific bits, place in ‘1’ at those positions, does not change destination
TEST Destination, mask
The result has 1 in tested position, IF, destination has 1’s in those positions, otherwise, result is zero, ZF=1
(if AL is even, even numbers has 0 at 0 position)
TEST AL,1
JZ Below ;yes

14. Test Instruction
Just Like CMP to SUB instruction, TEST instruction is the alternate to AND instruction
Used to Test specific bits, place in ‘1’ at those positions, does not change destination
TEST Destination, mask
The result has 1 in tested position, IF, destination has 1’s in those positions, otherwise, result is zero, ZF=1
(if AL is even, even numbers has 0 at 0 position)
TEST AL,1
JZ Below ;yes

15. Shift Instructions
Shifts the bits in DESTINATION to Right OR Left, One Place or More Place
There are two types of Shift Instruction
SHL (Shift Left)
SHR (Shift Right)
And
SAL (Shift Arithmetic Left)
SAR (Shift Arithmetic Right)

16. Shift Instructions There are two formats to write shift instruction
Opcode Destination, count OR
Opcode Destination, CL
SHL/SHR/SAL/SAR REG/MEM , count
SHL/SHR/SAL/SAR REG/MEM , CL
Count could be immediate value between 0 and 15

17. Shl Instruction Shift Number of bits to left in the destination
A ‘0’ is placed at LSB, MSB is shifted to CF
If more than 1 bits to be shifted, place value in CL register

18. Shl Instruction Affect on Flag
SF, PF, ZF reflect the result
AF is undefined
CF= last bit shifted out OF
For multishift OF is undefined
For Single Shift OF = 1 if MSB changes after shift

19. Sal Instruction Due to arithmetic nature of SHL, often SAL is used
Both Instructions produces the same result
MOV CL,3
SAL AL,CL
MULTIPLY AL BY 8

20. Shr Instruction Perform right shift on destination Format is:
SHR Destination, count
SHR Destination, 1
SHR Destination, CL
A zero is shift at MSB, LSB is shifted to CF

21. Sar Instruction
Equivalent to SHR instruction

22. Rotate Instructions
Shifts the bits within a register or memory location without discard
Two types of Rotate Instructions
ROL (Rotate Left)
ROR (Rotate Right)
And
RCL (Rotate through Carry Left)
RCR (Rotate through Carry Right)

23. Rotate Instruction
Shifts the bits within a register or memory location without discard
General Syntax Format
ROL/ROR/RCL/RCR REG/MEM , count
ROL/ROR/RCL/RCR REG/MEM , CL

24. Rol Instruction
Rotate Left bits are exited from MSB and entered in LSB, as well as, every bit that leave MSB copies itself in CF

25. Rol Instruction

26. Ror Instruction
Rotate Right bits are exited from LSB and entered in MSB, as well as, every bit that leave LSB copies itself in CF

27. Rcl Instruction
Rotate through Carry Left bits are exited from MSB and entered in CF and from CF entered in LSB, acts as CF is a part of operand

28. Rcr Instruction
Rotate through Carry right bits are exited from LSB and entered in CF and from CF entered in MSB, acts as CF is a part of operand

29. Application of Shifts and Rotate Instructions
Binary Input

30. Application of Shifts and Rotate Instructions
Binary Input

31. Application of Shifts and Rotate Instructions
Binary Output