On Sat, Jul 11, 2009 at 13:17, Heinz Czychun wrote: > Tried your suggestion and yes it didn't hurt, but also > didn't change the situation. Weird. A workaround for this is to rewrite your ISR. If you are never going to use the Timer0-interrupts you could simply ignore them. They will, in the strange environment of yours, trigger the IF of Timer0. What you can do in the ISR is clearing T0IF. So, your ISR could be rewritten to this: iServ movwf w_temp ; save off current W register contents movf STATUS,w ; move status register into W register movwf status_temp ; save off contents of STATUS register bcf INTCON, T0IF ; clear Timer0-IF btfsc PIR1,T1IF ; check Timer1-IF goto ServiceTimer1 goto iServ_Exit You will waste some cycles when Timer0 triggers but in case you cannot disable T0IE this could be a solution. -- - Rikard - http://bos.hack.org/cv/ -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist