How to quickly add and subtract in AVR

[Noman Yousaf]

in 8051 series there is very easy to add 2 digits in BCD. "DA" instruction is used for this. now in AVR i want to add 10 digits with 5 digits. how that is possible in very low time, just like using DA in 8051. but unluckily there is not any instruction in AVR instruction set. please help me.
i know 1 method.
by using "ADC", do all in "HEX" then convert it in BCD. but here is one more problem, there is not division in AVR so division takes long time by subtracting.

 

[Projetos_afg]

Re: AVR addition problem

You can use the Half Carry to do this. Here an simple code:

;R16 and R17 are bcd digits

	add	R16,R17		;Binary adition betwen R16 and R17
	brhc	No_HalfCarry
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;BCD Adjust
	andi	R16,0xF0	;Clear the low nibble
	ldi	R18,0x10	;
	add	R16,R18		;Add 1 to high nibble
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
No_HalfCarry:
	;code

 

[Noman Yousaf]

Re: AVR addition problem

Hi projetos_afg
i m sorry but it doesn't work. i made a routine. and wrote "ret" after "no_halfcarry:" and loaded 2 bcd values in r16 and r17 and ran this routine, the result was still in HEX, not BCD. please check it yourself and give me the right solution. thanks

 

[Projetos_afg]

Re: AVR addition problem

I'm sorry, I forgot the addiction by 6:

;R16 and R17 are bcd digits

	add	R16,R17		;Binary adition betwen R16 and R17
	brhc	No_HalfCarry
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;BCD Adjust
	ldi	R18,0x06	;
	add	R16,R18		;Add 1 to high nibble
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
No_HalfCarry:
	;code

 

[Noman Yousaf]

Re: AVR addition problem

Sorry
it is still not working