8051 Program to Multiply two 8 Bit numbers

Now we will try to multiply two 8-bit numbers using this 8051 microcontroller. The register A and B will be used for multiplication. No other registers can be used for multiplication. The result of the multiplication may exceed the 8-bit size. So the higher order byte is stored at register B, and lower order byte will be in the Accumulator A after multiplication.

We are taking two number FFH and FFH at location 20H and 21H, After multiplying the result will be stored at location 30H and 31H.  

Program

        MOV R0, #20H;set source address 20H to R0
    MOV R1, #30H;set destination address 30H to R1

        MOV A, @R0;take the first operand from source to register A
        INCR0; Point to the next location
        MOV B,@R0;take the second operand from source to register B

        MUL AB ;Multiply A and B

        MOV @R1, B; Store higher order byte to 30H
        INC R1; Increase R1 to point to the next location
        MOV @R1, A;Store lower order byte to 31H
HALT:   SJMP HALT ; Stop the program

8051 provides MULAB instruction. By using this instruction, the multiplication can be done. In some other microprocessors like8085, there was no MUL instruction. In that microprocessor, we need to use repetitive ADD operations to get the result of the multiplication. 

When the result is below255, the overflow flag OV is low, otherwise, it is 1.

Output

Ankith Reddy

Updated on: 27-Jun-2020

14K+ Views

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