Database

1. Boolean and Comparison Instructions (AND,
OR, NOT, XOR, TEST, CMP)
COMPUTER ORGANIZATION &
ASSEMBLY LANGUAGE

2. Boolean Instructions
Boolean instructions perform bitwise logical operations
between operands.
Instruction Description Example
AND Bitwise AND AND AX, BX
OR Bitwise OR OR AX, BX
XOR Bitwise Exclusive OR XOR AX, BX
NOT Bitwise NOT (1's complement) NOT AX
TEST Performs AND without storing
result
TEST AX, BX

3. Agenda Today
• Bitwise logical operator in Assembly and Masking
operations
• That is used by processor

4. Logical instructions
• There are 4 logical OP. AND OR XOR NOT
• Logical instructions refer to a set of instructions in
assembly language that perform operations based on
logical conditions.
• These instructions manipulate binary data, typically
expressed as bits (0s and 1s), to make decisions,
compare values, and control the flow of a program.
• Logical instructions are fundamental to constructing
decision structures, implementing conditional
statements, and managing the program's execution

5. AND instructions
• The "AND" operation is used to combine two binary values, typically expressed as bits, and
produces a result based on the logical conjunction of these values.

6. AND instructions
Condition
BOTH X , Y OP =1
OTHERWISE =0 lets, play with Emu8086
mov al, 10
mov bl, 11
AND al,bl
4bit convert into 8 for al and bl as well
0000 1010 = al
0000 1011 = bl
---------------------
0000 1010= AND

7. OR instructions
• The OR logical instruction is a binary operation that operates on
two sets of binary digits or Boolean values.
• In the context of computer programming and assembly language,
the OR instruction combines individual bits to produce a result
based on the logical OR operation.
Condition
IF ANY X , Y OP =1
OTHERWISE =0
Solve the problem
mov al, 8
mov bl, 9
OR al ,bl
4bit convert into 8 for al and bl as well
= al
= bl
---------------------
=OR

8. XOR instructions
• XOR, which stands for "exclusive OR," is a logical instruction and a bitwise operation used in computer
programming and digital logic design. The XOR operation is applied to two binary values, and its result is
determined by the following rules:
• If the two corresponding bits are different (one is 0 and the other is 1), the XOR operation yields 1.
• If the two corresponding bits are the same (both 0 or both 1), the XOR operation yields 0.
Condition
IF X , Y OP same =0
OTHERWISE =1
Solve the problem
mov al, 11
mov bl, 13
xor al ,bl
4bit convert into 8 for al and bl as well
= al
= bl
---------------------
=XOR

9. NOT instructions
• The NOT logical instruction, often represented as "NOT" or "~" in various programming languages and
assembly languages, performs a bitwise negation operation.
• Its primary function is to invert the individual bits of a binary value, changing each 0 to 1 and each 1 to 0.
Here's a simple representation:
If A is a binary value, then NOT A results in a new binary value where each bit of A is flipped (0s
become 1s, and 1s become 0s).
Condition
IF X OP 0=1
IF X OP 1=0
Solve the problem
mov al, 14
NOT al
4bit convert into 8 for al for single input
= al
---------------------
=NOT al

10. Test Instruction
The TEST instruction performs a bitwise AND between two operands,
just like the AND instruction, but it does not store the result. Instead, it
only updates the CPU flags (in the FLAGS register), which can be used
for conditional branching.
Syntex:
TEST destination, source

11. Comparison Instructions (CMP)
• In Assembly language, Boolean and Comparison Instructions (CMP)
are used to evaluate conditions and make decisions in programs.
These instructions are fundamental for implementing loops,
conditional branching, and logic operations.

12. Types of Masking
1. Selective bit clearing
2. Selective bit setting
3. Selective bit inversion
4. Selective bit testing

13. Conclusion
• Bit masking is widely used in programming, especially in low-level and embedded systems,
because it provides a fast and efficient way to manipulate specific bits of data.
Example Use Case: Enabling/Disabling Features in a Device
Suppose a hardware register uses the following bits to control features
Bit 0: Enable LED
Bit 1: Enable
FanBit 2: Enable Motor Using bit masking:
• Enable the LED: OR the register with 0b00000001.
• Disable the Fan: AND the register with 0b11111101.

14. Compare instruction and its types
• In Assembly, a jump instruction changes the flow of execution to a
different part of the program.
• We can learn compare after learning the jumps.

15. Jump(instruction to control the program flow)
1.Unconditional Jump
• Unconditional Jump jump to label
without any condition
• Syntax
jmp label
L1:
Mov dl, “H”
Mov ah, 02
Int 21H
jmp L1
2.Conditional Jump
• Unconditional Jump jump to label when
condition occur.
• Syntax: Opcode label
L1:
Mov ah, 01
Int 21H
Mov dl, 3
Cmp al,dl
JE L1

16. Unsigned numbers
Conditional jump instructions for unsigned comparisons: explaining the jump
instructions JE, JNE, JB, JA, JAE, JBE

18. Simple Compare example 2
Mov al, 5 ; Load 5 into AL
Mov bl, 5 ; Load 5 into BL
Cmp al, bl ; Compare AL and BL (5 - 5 = 0)
; Zero Flag (ZF) is set to 1 because the result is 0
Mov al, 5 ; Load 5 into AL
Mov bl, 3 ; Load 3 into BL
Cmp al, bl ; Compare AL and BL (5 - 3 = 2)
; Zero Flag (ZF) is set to 0 because the result is not 0

19. 1/JE compared values are equal. ZF=1
otherwise 0
L1:
Mov ah, 01
Int 21H
Mov dl, 3
Cmp al,dl
JE L1
Hint 3 = 3 (Main logic 3-3=0) ZF=1

20. Simple Compare example 3
L1:
Mov ah, 01 ;2
Int 21H ;term
Mov dl, 3 ;3equal in hex 51
Sub al, 48 ;51-48=3
Cmp dl, al ;3-3=
JE L1

21. 2/JNE =Jumps if the two compared values are
not equal Then (ZF=0) otherwise 1
L1:
Mov ah, 01
Int 21H
Mov dl, 51
Cmp al,dl
JNE L1
Hint input 10 ≠3

22. 3/JB =Jumps if the first value is less than the
second value then CF = 1 otherwise 0
L1:
Mov ah, 01
Int 21H
Mov dl, 51
Cmp al,dl
JB L1
Hint input 1 <3

23. 4/JA =Jumps if the first value is greater than
the second. CF = 0 & ZF=0
L1:
Mov ah, 01
Int 21H
Mov dl, 51
Cmp al,dl
JA L1
Hint input 5>3

24. 5/JAE =jumps if the first value is greater than
or equal then CF = 0 otherwise 1
L1:
Mov ah, 01
Int 21H
Mov dl, 51
Cmp al,dl
JB L1
Hint input 3>=3

25. 6/JBE =Jumps if the first value is less than or
equal. CF = 1 & ZF=1
L1:
Mov ah, 01
Int 21H
Mov dl, 51
Cmp al,dl
JBE L1
Hint input 1=<3

26. Brief Recap of Flags
 Carry Flag (CF):
 Set (1): If there is a borrow during an unsigned subtraction (i.e., if the first operand is less than the
second).
 Cleared (0): If no borrow occurs.
 Zero Flag (ZF):
 Set (1): If the result of the operation is zero (operands are equal).
 Cleared (0): If the result is non-zero.
 Sign Flag (SF):
 Set (1): If the most significant bit (MSB) of the result is 1 (negative for signed operations).
 Cleared (0): If the MSB is 0 (positive or zero for signed operations).
 Overflow Flag (OF):
 Set (1): If a signed operation produces a result outside the range of the destination's signed
representation.
 Cleared (0): If no overflow occurs.
 Parity Flag (PF):
 Set (1): If the result has an even number of 1 bits.
 Cleared (0): If the result has an odd number of 1 bits.
 Auxiliary Carry Flag (AF):
 Set (1): If there is a carry/borrow out of bit 3 during the operation.
 Cleared (0): If no carry/borrow occurs.

27. Text Books refrence:
• Assembly Language Step-by-Step: Programming with DOS and Linux
Jeff Duntemann
• Introduction to 80X86 Assembly Language and Computer Architecture
Richard C. Detmer.