Instruction Set and Assembler Directives in Assembly Language

Instruction Set and Assembler Directives in Assembly Language (MASM) When you're learning assembly language programming, it's important to understand the Instruction Set and Assembler Directives. These are the fundamental parts of an assembly program. The Instruction Set is a collection of commands (instructions) that a processor can execute. Each instruction includes an opcode (operation code) and, sometimes, one or more operands. It's worth noting that the instruction set is specific to a particular architecture, such as x86 for MASM. Categories of Instructions The instruction set can be categorized into several groups based on the function of the instructions: 1. Data Transfer Instruction 2. Arithmetic Instructions 3. Logical Instructions 4. Control Transfer Instructions 5. Bit Manipulation Instructions 1. Data Transfer Instructions These instructions move data between registers, memory, and I/O devices. Instruction MOV Syntax MOV dest, source PUSH POP PUSH reg/mem/imm POP reg/mem XCHG IN OUT XCHG reg, reg/mem IN AX, DX OUT DX, AX Description Moves data from the source to the destination Pushes the operand onto the stack Pops the top of the stack into the operand Exchanges the contents of two operands Reads data from an I/O port Sends data to an I/O port Example: MOV AX, BX ; Moves data from BX to AX PUSH AX ; Pushes AX onto the stack POP CX ; Pops the top of the stack into CX XCHG AX, BX ; Exchanges the values of AX and BX 2. Arithmetic Instructions** These perform basic arithmetic operations like addition, subtraction, multiplication, and division. Instruction ADD SUB MUL DIV INC DEC Syntax ADD dest, source SUB dest, source MUL reg/mem DIV reg/mem INC reg/mem DEC reg/mem Description Adds source to destination Subtracts source from destination Multiplies unsigned AX by the operand Divides AX by the operand Increments the operand by 1 Decrements the operand by 1 Example ADD AX, BX ; Adds BX to AX SUB AX, 1 ; Subtracts 1 from AX MUL BX ; Multiplies AX by BX, result in DX:AX DIV BX ; Divides AX by BX, quotient in AX, remainder in DX 3. Logical Instructions These instructions perform bitwise logical operations like AND, OR, XOR, and NOT. Instruction AND Syntax AND dest, source OR OR dest, source XOR XOR dest, source NOT TEST NOT reg/mem TEST dest, source Description Performs bitwise AND between dest and source Performs bitwise OR between dest and source Performs bitwise XOR between dest and source Inverts the bits of the operand Performs AND but doesn't store result Example: AND AX, BX OR AX, 1 XOR AX, BX NOT AX TEST AX, BX ; Bitwise AND between AX and BX ; Bitwise OR between AX and 1 ; Bitwise XOR between AX and BX ; Bitwise NOT of AX ; Tests if any bit in both AX and BX is set 4. Control Transfer Instructions These instructions control the flow of the program, like jumping to different parts of the code or calling procedures. Instruction JMP JE/JZ JNE/JNZ CALL RET INT Instruction JMP JE/JZ JNE/JNZ CALL RET INT Syntax JMP label JE/JZ label JNE/JNZ label CALL label RET INT n Syntax JMP label JE/JZ label JNE/JNZ label CALL label RET INT n Description Unconditional jump to label Jump if equal/zero flag is set Jump if not equal/zero flag is clear Calls a procedure Returns from a procedure Software interrupt Description Unconditional jump to label Jump if equal/zero flag is set Jump if not equal/zero flag is clear Calls a procedure Returns from a procedure Software interrupt Example: CMP AX, BX ; Compare AX with BX JE EQUAL ; Jump to label EQUAL if AX == BX JMP NEXT ; Unconditionally jump to NEXT EQUAL: MOV CX, 0 ; If AX == BX, execute this NEXT: 5. Bit Manipulation Instructions These instructions shift and rotate bits within a register or memory operand. Instruction SHL/SAL SAL Syntax SHL dest, count SAL destination, count Description Shift logical left Shift Arithmetic Left