Addition of two 8-bit numbers
data segment
a db 09h
b db 0fh
c dw ?
data ends
code segment
assume cs:code, ds:data
start:
mov ax, data
mov ds, ax
mov al, a
mov bl, b
add al, bl
mov c, ax
mov ah,4ch
int 21h
code ends
end start Understand the code
Data Segment:
data segment: This section defines the variables.
a db 09h: Declares an 8-bit byte variable a initialized to 09h (hexadecimal).
b db 02h: Declares an 8-bit byte variable b initialized to 02h.
c dw ?: Declares a 16-bit word variable c to store the sum. We use a 16-bit variable to handle potential overflow if the sum exceeds 255 (FFh).
Code Segment:
code segment: This section contains the program instructions. ; assume cs:code,ds:data: Tells the assembler that the cs register points to the code segment and the ds register points to the data segment.
start: The label marking the program’s entry point.
mov ax,data: Loads the address of the data segment into the ax register.
mov ds,ax: Sets the ds register to point to the data segment. This is crucial for accessing the variables a and b.
mov al,a: Loads the value of a (09h) into the al register (the lower 8 bits of ax).
mov bl,b: Loads the value of b (02h) into the bl register (the lower 8 bits of bx).
add al,bl: Adds the contents of bl to al. The result (0Bh) is stored in al.
mov c,ax: Moves the contents of ax (which now contains the sum in its lower byte, al) into the variable c.
int 3: The breakpoint instruction halts execution for debugging purposes.
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