> So I would like to implement a running average algorithm, which gives the
> average of the last eight values. It should add up the last eight values
> and divide then by 8. but my values can be everything between 256 and 0.
> If I divide every value before adding them up I get very arbitrary
> averages from low input numbers due to rounding errors. Is there a
> possibility to do 16 bit integer arithmetric with two data registers.


How 'bout something like this?

;initialization
                clrf            sum1
                clrf            sum2

;add in new number (num) - 16 bit addition
                movf            num, W
                addwf           sum1, F
                clrw
                btfsc           STATUS, C
                movlw           1
                addwf           sum2, F
                return

;find average - don't care what's rotated into sum2
                movlw           3
                movwf           temp
loop    rrf                     sum2, F
                rrf                     sum1, F
                decfsz          temp, F
                goto            loop
;sum1 contains the result

15 instructions, 1 non-global temp register, 2 global sum registers, 98
cycles (including calls to addition routine)

By the way, this only works for values 0-255.  I haven't tested this, so
I could be totally wrong.

Jason Harris