Multiplication

1.  Program for multiplication of two 8-bit numbers stored at memory location 5001H and 5002H.

	;<Program for multipication of two 8-bit numbers
	;stored at memory locations 5001H and 5002H. The
	;result is stored at 5003H and 5004H.>
	jmp start
	;code
	start: lda 5001h
	mov b,a
	lda 5002h
	mov c,a
	mvi a, 00h
	mvi d, 00h
	loop1: add b
	jnc loop2
	inr d
	loop2: dcr c
	jnz loop1
	sta 5003h
	mov a,d
	sta 5004h
	hlt

view raw simple_multiply.asm hosted with ❤ by GitHub

The multiplication of two 8-bit numbers can generate a result of maximum 16-bits. so the final result is stored at 5003H (Lower 8-bit) and 5004H (Higher 8-bit). See the content of the memory locations. The result of operation is 500 (decimal) or 1F4 (Hex) or 256 (Higher 8-bit) + 244 ( Lower 8-bit) = 500.

2.   Program for multiplication of two signed 8-bit numbers. The result should also be in the signed number format. Assume the result is limited to 8-bit only with MSB as the sign bit.

	;<Program for multiplication of two 8-bit signed
	;numbers.>
	jmp start
	;code
	start: lda 5001h
	mov b,a
	ani 80h
	mov d,a
	lda 5002h
	mov c,a
	ani 80h
	mov e,a
	mvi a, 7fh
	ana b
	mov b,a
	mvi a, 7fh
	ana c
	mov c,a
	mov a,e
	xra d
	mov d,a
	mvi a, 00h
	loop1: add b
	dcr c
	jnz loop1
	add d
	hlt

view raw signed_multiplication.asm hosted with ❤ by GitHub

The result is shown for the numbers 84H (-4 in decimal) and 82H (-2 in decimal). See the content of accumulator which is 08H ( -4 x -2 = +8 in decimal). 

Note: The MSB represents the sign of the number. Refer here for more explanation on signed number representation. 

Again, result is shown for the numbers 84H (-4 in decimal) and 02H (2 in decimal). See the content of accumulator which is 88H ( -4 x 2 = -8 in decimal).