This is NON-Keil, but part of our "embedded" world. I found this Texas Instruments website for filters that is kind of cool...
www-k.ext.ti.com/.../webcgi.exe(26717),new
I guess, you'll have to copy and paste the URL to get it since it is so long.
Enjoy,
--Cpt. Vince Foster 2nd Cannon Place Fort Marcy Park, VA