AVR-Chat

At 06:32 PM 12/3/2004, John Samperi wrote:


>At 10:54 AM 3/12/04 -0000, you wrote:
> >
> >Ok, and the final soloution is ;-
> >
> >mov r30, step
> >ldi r31, high(array<<1)
> >add r31, num
> >lpm r18, z
> >out portd, r18
> >
> >As I'm only using Bytes not Words, I didn't need to left shift the ZL (r30)
> >value.
>
>But DOES IT WORK? :-) The flash is in 2 byte lots (16 bit) that is the reason
>you need to multiply by 2 to get to the address.

Doesn't look entirely sane to me..

 >mov r30, step
 >ldi r31, high(array<<1)

Not sure what step is, but we are now pointing at high(Array*2)+Step

 >add r31, num

Ok, adding offset, but this assumes that Step + num will never be > 255.

 >lpm r18, z
 >out portd, r18

Conventional..


What I would do, is this:

ldi     zl,low(Array*2) ;Point at the array
ldi     zh,high(Array*2)

clr     TEMP2 ;or any suitable register
add     zl,step         ;16 bit op
adc     zh,TEMP2

add     zl,num          ;16 bit op
adc     zh,TEMP2

lpm     r18,z
out     portd,r18

But I'm not sure how step is used here, so the first 16 bit add might not 
really be the right thing.