Why do you care if it gets to 255 or just 254 ?

The error is pretty small.

Tal

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Edson Brusque (listas)
> Sent: Thursday, June 13, 2002 4:54 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [PIC]: Software low pass filtering
>
>
> Hello All,
>
>
>     some months ago Olin posted the formula that changed DSP world: :)
>         Filt <-- Filt + (New - Filt)*FFrac
>
>     Saddly, my 8 bit implementation have a problem that I can't surpass:
>         filt = filt + ((sig16)new - (sig16)filt) / 2;
>
>     The value never goes to 255 because of integer roundings:
>         filt = 254 + (255 - 254) / 2;
>         filt = 254 + (1)/2;
>         filt = 254;
>
>     There's a way to change this? I've tried to raise the
> resolution making:
>         filt = filt + ((sig16)new*2 - (sig16)filt*2 + 1) / 4;
>
>     But got same results because:
>         filt = 254 + ((sig16)255*2 - (sig16)254*2 + 1) / 4;
>         filt = 254 + (510 - 508 + 1) / 4;
>         filt = 254 + (510 - 508 + 1) / 4;
>         filt = 254 + (1) / 4;
>
>     Please, someone help me!!!
>
>     Best regards,
>
>     Brusque
>
> -----------------------------------------------------------------
> Edson Brusque                 C.I.Tronics Lighting Designers Ltda
> Research and Development               Blumenau  -  SC  -  Brazil
> Say NO to HTML mail                          www.citronics.com.br
> -----------------------------------------------------------------
>
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