8051 Program – division 16bit

;16bit division
; R1 R0
; / R3 R2
; = R3 R2
; shift left the divisor such that the number of digits
; in the divisor is the same as the number of digits in the dividend
; shift right the divisor and substract this shifted divisor from the dividend
; repeat the process again until the divisor has shifted into its original position
	ORG 0H
MAIN:
	MOV R0,#0B3H	;Load the divident value into R6 and R7
	MOV R1,#00H
	MOV R2,#08H	;Load the divisor value into R4 and R5
	MOV R3,#00H
	LCALL DIV_16
	SJMP MAIN
DIV_16:
	CLR C	;Clear carry initially
	MOV R4,#00h	;Clear R4 working variable initially
	MOV R5,#00h	;CLear R5 working variable initially
	MOV B,#00h	;Clear B since B will count the number of left-shifted bits
lshift:
	INC B	;Increment counter for each left shift
	MOV A,R2	;Move the current divisor low byte into the accumulator
	RLC A	;Shift low-byte left, rotate through carry to apply highest bit to high-byte
	MOV R2,A	;Save the updated divisor low-byte
	MOV A,R3	;Move the current divisor high byte into the accumulator
	RLC A	;Shift high-byte left high, rotating in carry from low-byte
	MOV R3,A	;Save the updated divisor high-byte
	JNC lshift	;Repeat until carry flag is set from high-byte
rshift:		;Shift right the divisor
	MOV A,R3	;Move high-byte of divisor into accumulator
	RRC A	;Rotate high-byte of divisor right and into carry
	MOV R3,A	;Save updated value of high-byte of divisor
	MOV A,R2	;Move low-byte of divisor into accumulator
	RRC A	;Rotate low-byte of divisor right, with carry from high-byte
	MOV R2,A	;Save updated value of low-byte of divisor
	CLR C	;Clear carry, we don't need it anymore
	MOV 07h,R1	;Make a safe copy of the dividend high-byte
	MOV 06h,R0	;Make a safe copy of the dividend low-byte
	MOV A,R0	;Move low-byte of dividend into accumulator
	SUBB A,R2	;Dividend - shifted divisor = result bit (no factor, only 0 or 1)
	MOV R0,A	;Save updated dividend
	MOV A,R1	;Move high-byte of dividend into accumulator
	SUBB A,R3	;Subtract high-byte of divisor (all together 16-bit substraction)
	MOV R1,A	;Save updated high-byte back in high-byte of divisor
	JNC result	;If carry flag is NOT set, result is 1
	MOV R1,07h	;Otherwise result is 0, save copy of divisor to undo subtraction
	MOV R0,06h
result:
	CPL C	;Invert carry, so it can be directly copied into result
	MOV A,R4
	RLC A	;Shift carry flag into temporary result
	MOV R4,A
	MOV A,R5
	RLC A
	MOV R5,A
	DJNZ B,rshift	;Now count backwards and repeat until "B" is zero
	MOV R3,05h	;Move result to R3/R2
	MOV R2,04h	;Move result to R3/R2
	RET
	END

---

<< Previous :: Up :: Next >>

---

Related topics:
8051 Program - arithmetic operation 8bit   |   8051 Program - addition 8bit   |   8051 Program - subtraction 8bit   |   8051 Program - multiplication 8bit   |   8051 Program - division 8bit   |   8051 Program - addition 16bit   |   8051 Program - subtraction 16bit   |   8051 Program - multiplication 16bit   |   8051 Program - addition multibyte   |   8051 Program - multiplication 16bit by 8bit   |   8051 Program - addition 8bit 2digit bcd   |   8051 Program - memory subroutines   |   8051 Program - math subroutines   |   8051 Program - conversion subroutines

---

List of topics: 8051

---