8086 MASM Assembly Program for Addition of Two 8-bit Numbers

This blog post will guide you through a MASM (Microsoft Macro Assembler) program that performs the addition of two 8-bit numbers. While this is a fundamental operation, it demonstrates crucial assembly programming concepts such as data handling, register usage, and memory storage. Let’s dive in!

Assembly Code

    .model small
    .data
    a db 09h
    b db 02h
    c dw ?
    
    .code
    main proc
        mov ax, @data
        mov ds, ax
        
        mov al, a
        mov bl, b
        add al, bl
        
        mov ah, 0
        mov c, ax
        
        int 3  ; Breakpoint interrupt
        
        mov ax, 4C00h  ; Exit program
        int 21h
    main endp
    
    end main

Understanding the Code

The program consists of two main sections: the data segment and the code segment.

Data Segment:

a db 09h → Defines an 8-bit variable a with the value 09h.
b db 02h → Defines an 8-bit variable b with the value 02h.
c dw ? → Defines a 16-bit variable c to store the result, ensuring space for potential overflow.

Code Segment:

mov ax, @data → Loads the address of the data segment into the ax register.
mov ds, ax → Sets the ds (Data Segment) register to access the defined variables.
mov al, a → Loads the value of a into the al register.
mov bl, b → Loads the value of b into the bl register.
add al, bl → Adds the value of bl to al, storing the sum in al.
mov ah, 0 → Clears the upper byte to store the result correctly in ax.
mov c, ax → Stores the computed sum in the memory location c.
int 3 → Interrupt for debugging purposes.
mov ax, 4C00h → Terminates the program cleanly using DOS interrupt 21h.

Flowchart

High-Level Overview

Data Initialization: Declares two 8-bit variables (a and b) and reserves memory for the sum (c).
Segment Setup: Loads and configures the data segment to access variables.
Value Loading: Retrieves values of a and b into CPU registers.
Addition Operation: Computes the sum using the ADD instruction.
Result Storage: Saves the sum in a memory location.
Program Termination: Stops execution using int 3 and DOS exit call.

Running the Program

To assemble, link, and execute the program, follow these steps:

Assemble the Code:masm masm_add.asm;
Link the Object File:link masm_add.obj;
Run in Debugger:debug masm_add.exe

Memory Dump Analysis

After running the program, inspecting the memory reveals:

09 02 0B 00 00 00 00 00-00 00 00 00 00 00 00 00

09: Represents a.
02: Represents b.
0B: Represents the computed sum 0Bh stored in c.

Conclusion

This MASM assembly program demonstrates the core concepts of handling 8-bit arithmetic in assembly language. Though simple, it forms the foundation for more complex operations in low-level programming.

Happy coding! ⚡

@ankurm