From: "Olin Lathrop"
> Two cascaded single pole filters each
> with a filter fraction of 1/256 looks like would work well here
>   new filt val <-- <old filt val> - <old filt val>/256 + <input =
val>/256

Ok, just disregard prev msg. Dunno what I was thinking when I wrote that =
crap.

The filter isnt quite ok. It counts up when I'd expect it do count down, =

and vice versa. The high byte overflows in one direction.
The high byte looks like it basically works as filter output (when =
overflow fixed)

The low byte is just plain nuts... With 0 as sample input it keeps=20
counting in a set speed. With 255 as sample input it it also keep
counting, but the counting freq isnt constant. It looks more like a =
binary
count on the LEDs. I would have expected it to be 0 all the time with
0 as input !


; When we come here we have done 255 samples, 1 byte each for Chan A & =
B.
; The new sample values are available in sampleA & sampleB
; Now calculate the filtered values for both values :=20
;   new =3D old - old/256 + input/256
; Filtered output should be in FilterAH, FilterAL when done here

FILTER_A    ; // Single pole filter //
     ; new =3D old - old/256 + input/256

     ; // calc: 'input/256' //
  movfw sampleA  ; save old value.=20
  movwf tempL  ; move high-byte to low-byte makes /256
  clrf tempH  ; set highbyte to 0
     ; Now 'input/256' is in tempH:tempL

     ; // calc: 'old/256' //
  movfw FilterAH ; get old value.=20
  movwf temp1L  ; move high-byte to low-byte makes /256
  clrf temp1H  ; set highbyte to 0
     ; Now 'old/256' is in temp1H:temp1L
 =20
     ; // calc: 'old' - 'old/256' //
  movf temp1L, W
  subwf FilterAL, F ; *** ska det vara F eller W ???
  movf temp1H, W
  btfss STATUS,C
  incfsz temp1H, W
  subwf FilterAH, F ; *** ska det vara F eller W ???
     ; Now 'old'-'old/256' is in FilterAH:FilterAL

     ; // Calc: 'result above' + 'input/256' //
  movfw tempL  ; get result from 'input/256'
  addwf FilterAL, F ; add to the result from ['old'-'old/256']
  btfss STATUS,C ; any carry ?
  incfsz FilterAH, F ; if carry then high byte +1
     ; Now FINAL RESULT should be in FilterAH:FilterAL !

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