Sorry I meant timer 1! Thanks Graham Hi, Could someone please give me some help on hoe to work out TMR1H and TMR1L so that I get an interupt on rollover every 2.275ms on a 16F877. Does someone have a formula that you can 'plug' values into. Thanks Graham North _________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics _________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics