A microprocessor is an electronic component that is used by a computer to do its work. It is a central processing unit on a single integrated circuit chip containing millions of very small components including transistors, resistors, and diodes that work together. Some microprocessors in the 20th century required several chips. Microprocessors help to do everything from controlling elevators to searching the Web. Everything a computer does is described by instructions of computer programs, and microprocessors carry out these instructions many millions of times a second. [1] Microprocessors were invented in the 1970s for use in embedded systems. The majority are still used that way, in such things as mobile phones, cars, military weapons, and home appliances. Some microprocessors are microcontrollers, so small and inexpensive that they are used to control very simple products like flashlights and greeting cards that play music when you open them. A few especially powerful microprocessors are used in personal computers.

1. Logical Instructions
–These are the instructions used for basic
logic operations such as AND, OR, NOT and
XOR.
–These are also used for carrying out bit by
bit operations such as shift (SHR,SHL) or
rotate (ROL,ROR,RCR,RCL).
– One more Instruction under this category is
TEST instruction.

2. AND (Logical AND)
Syntax :-- AND destination, source
• This instruction is used to bit by bit AND the
contents of source to the destination.
•The result is stored in the destination.
•The source operand can be a immediate, a
register or a memory location.
•The destination can be a register or a memory
location, but not an immediate data.
•Both operands cannot be immediate data or
memory location.
•Flags affected : OF = 0 ,CF = 0 , AF is undefined.
• And other flags (SF, ZF, PF) are affected based on
the AND operation.

3. • Operation Performed :--
• Destination  Destination AND source
• Examples :--
1. AND BH,CL ;AND byte in CL with Byte in BH,
result in BH.
2. AND BX,00FFH ;AND word in BX with immediate
data 00ffH
3. AND [5000H], DX ;AND word in DX with a
word in memory with offset
5000 in DS.
AND (Logical AND) contd..

4. Numeric Example
If AX = 3F0F,
After Instruction,
AND AX,9078H ; AX  AX AND 0008H
;AX  3F0F AND 0008
3F0F  0011 1111 0000 1111
AND
9078  1001 0000 0111 1000
-------------------------------------
= 0001 0000 0000 1000
1008H in AX register

5. OR (Logical OR)
Syntax :-- OR destination, source
• This instruction is used to bit by bit OR the
contents of source to the destination.
•The result is stored in the destination.
•The source operand can be a immediate, a
register or a memory location.
•The destination can be a register or a memory
location, but not an immediate data.
•Both operands cannot be immediate data or
memory location.
•Flags affected : OF = 0 ,CF = 0 , AF is undefined.
• And other flags (SF, ZF, PF) are affected based on
the OR operation.

6. • Operation Performed :--
• Destination  Destination OR source
• Examples :--
1. OR BH,CL ;OR byte in CL with Byte in BH,
result in BH.
2. OR BX,00FFH ;OR word in BX with immediate
data 00ffH
3. OR [5000H], DX ; OR word in DX with a
word in memory with offset
5000 in DS.
OR (Logical OR) contd..

7. Numeric Example
If AX = 3F0F,
After Instruction,
OR AX,9078H ; AX  AX OR 9078H
;AX  3F0F OR 9078
3F0F  0011 1111 0000 1111
OR
9078  1001 0000 0111 1000
-------------------------------------
= 1011 1111 0111 1111
BF7FH in AX register

8. XOR (Logical XOR)
Syntax :-- XOR destination, source
• This instruction is used to bit by bit XOR the
contents of source to the destination.
•The result is stored in the destination.
•The source operand can be a immediate, a
register or a memory location.
•The destination can be a register or a memory
location, but not an immediate data.
•Both operands cannot be immediate data or
memory location.
•Flags affected : OF = 0 ,CF = 0 , AF is undefined.
• And other flags (SF, ZF, PF) are affected based on
the XOR operation.

9. • Operation Performed :--
• Destination  Destination XOR source
• Examples :--
1. XOR BH,CL ;XOR byte in CL with Byte in BH,
result in BH.
2. XOR BX,00FFH ;XOR word in BX with immediate
data 00ffH
3. XOR [5000H], DX ; XOR word in DX with a
word in memory with offset
5000 in DS.
XOR (Logical XOR) contd..

10. Numeric Example
If AX = 3F0F,
After Instruction,
XOR AX,9078H ; AX  AX XOR 0008H
;AX  3F0F XOR 0008
3F0F  0011 1111 0000 1111
XOR
9078  1001 0000 0111 1000
-------------------------------------
= 1010 1111 0111 0111
AF77H in AX register

11. NOT (Logical Invert )
Syntax :-- NOT destination
• This instruction complements (inverts) each
bit of the byte or word stored in the
destination.
•The result is stored in the destination.
•The destination can be a register or a memory
location.
•No Flags affected

12. • Operation Performed :--
• Destination  NOT Destination
• Examples :--
1. NOT BH ;Complement byte in BH, result in BH.
2. NOT BX ; Complement word in BX, result in BX.
3. NOT BYTE PTR [5000H] ; Complement byte
in memory with offset 5000 in DS.
NOT (Logical Invert ) contd..

13. Numeric Example
If AX = 3F0F,
After Instruction,
NOT AX ; AX  NOT AX
;AX  NOT 3F0F
3F0F  0011 1111 0000 1111
Complement
-------------------------------------
= 1100 0000 1111 0000
C0F0H in AX register

14. TEST (Logical compare )
Syntax :-- TEST destination, source
• This instruction is used to bit by bit AND the
contents of source to the destination.
•The result is not stored in the destination.
•The source operand can be a immediate, a
register or a memory location.
•The destination can be a register or a memory
location, but not an immediate data.
•Both operands cannot be immediate data or
memory location.
•Flags affected : OF = 0 ,CF = 0 , SF, ZF, PF.
•TEST instruction is used to set flags before a
conditional jump instruction

15. • Operation Performed :--
– Flags  set result of Destination AND source
• Examples :--
1. TEST BH,CL ;AND byte in CL with Byte in BH,
no result but flags are affected.
2. TEST BX,00FFH ;AND word in BX with immediate
data 00ffH, no result but flags are
affected.
3. TEST DX, [5000H];AND word in DX with a word in
memory with offset 5000 in DS,
no result but flags are affected.
TEST (Logical Compare) contd..

16. SHL / SAL (Shift Logical/Arithmetic Left)
Syntax :-- SHL/SAL destination, count
• SHL & SAL are the opcodes for the same
operation
•This instruction shifts the destination bit by bit to
the left and insert zeroes in the newly introduced
least significant bits.
•The shift operation is through carry.
•The count can be either 1 or specified by CL
register.
•The destination can be a byte or a word in
register or a memory location, but not an
immediate data.
•Flags affected : OF ,CF, SF, ZF, PF.
•These instructions can be used to multiply an
unsigned number by power of 2.

17. CF BX
0
0
1
CF BX
• Operation Performed :--
–CF  MSB ------------------ LSB  0
• Example :--
– If CF = 0, BX = E6D3H
– After SAL BX, 1 ; Shift the contents of BX
register by one towards left
SHL / SAL (Shift Logical/Arithmetic Left)Cntd..
1 1 1 0 0 1 1 0 1 1 0 1 0 0 1 1
1 1 0 0 1 1 0 1 1 0 1 0 0 1 1 0
BX = CDA6

18. • Example :--
• Use of SHL instruction for Multiplication:-
– If CF = 0, BH = 04H
– MOV CL, 03 ; Load CL register for
the count
– SHL BH, CL ; Shift the contents
of BX register by one
towards left
– BH = 20H (32D) [ 04 * 23 = 32 D]
– Note :-- SHL can be used to multiply a number
with powers of 2.
SHL / SAL (Shift Logical/Arithmetic Left)Cntd..

19. 0 0 0 1 0 0 0 0
CF BH
0
0
0
0
0
0
0
SHL / SAL (Shift Logical/Arithmetic Left)Cntd..
BH = 20H with CF = 0
0 0 0 0 0 1 0 0
0 0 0 0 1 0 0 0
0 0 1 0 0 0 0 0

20. SAR (Shift Arithmetic Right )
Syntax :-- SAR destination, count
• This instruction shifts the destination bit by bit to
the right and MSB position is kept in the old MSB
position
•The shift operation is through carry, LSB is shifted
to CF.
•The count can be either 1 or specified by CL
register.
•The destination can be a byte or a word in
register or a memory location, but not an
immediate data.
•Flags affected : OF ,CF, SF, ZF, PF.
•This instruction can be used to divide an unsigned
number by power of 2.

21. BX CF
0
1
BX CF
1 1 1 1 0 0 1 1 0 1 1 0 1 0 0 1
• Operation Performed :--
– MSB ----------------- LSB  CF
• Example :--
– If CF = 0, BX = E6D3H
– After SAR BX, 1 ; Shift the contents of BX
register by one towards right
SAR (Shift Arithmetic Right)Cntd..
1 1 1 0 0 1 1 0 1 1 0 1 0 0 1 1
BX = F369H

22. • Example :--
• Use of SAR instruction for Division:-
– If CF = 0, BH = 14H
– MOV CL, 02 ; Load CL register for the
count
– SAR BH, CL ; Shift the contents
of BX register by one
towards right
– BH = 05H (20D) [ 20 / 22 = 5D]
– Note :-- SAR can be used to divide a number with
powers of 2 and get the quotient.
SAR (Shift Arithmetic Right )Cntd..

23. 0 0 0 0 0 1 0 1
BH CF
0
0
0
SAR (Shift Arithmetic Right)Cntd..
BH = 05H with CF = 0
0 0 0 1 0 1 0 0
0 0 0 0 1 0 1 0

24. SHR (Shift Logical Right)
Syntax :-- SHR destination, count
•This instruction shifts the destination bit by
bit to the right and insert zeroes in the newly
introduced most significant bits.
•The shift operation is through carry.
•The count can be either 1 or specified by CL
register.
•The destination can be a byte or a word in
register or a memory location, but not an
immediate data.
•Flags affected : OF ,CF, SF, ZF, PF.

25. 1 1 1 1 0 0 1 1 0 1 1 0 1 0 0 1
BX CF
0
0
1
BX CF
• Operation Performed :--
–0  MSB ------------------ LSB  CF
• Example :--
– If CF = 0, BX = E6D3H
– After SHR BX, 1 ; Shift the contents of BX
register by one towards right
SHR (Shift Logical Right)Cntd..
1 1 1 0 0 1 1 0 1 1 0 1 0 0 1 1
BX = F369H