Hi, Another problem, with my filter program, the ISR never gets called! Its supposed to be called every 1/300 s, at which PORTB is to be read. [I have used a intial TMR0 value of 47 and a prescaler of 16 to get the 1/300 s delay.] Any ideas?? Thanks for your replies. [past & future] Regards, Saurabh Content-Type: application/octet-stream; name="latest.asm" Content-Disposition: attachment; filename="latest.asm" Attachment converted: growth:latest.asm (????/----) (00008E12)