(oops...sorry forgot tag) Using w98; MPLAB 5.40.00 I need an accurate time period on a 12C509 and testing code on a JW device. Made a note of the internal calibration value before erasing. Using TMR0 and internal oscillator for timing - set the up the calibration constant in the Calibration window in MPLAB. Here is my problem....when I test on MPLAB simulator the timing period if fine and correct for a time period of 1 second I get 999.94 mS. But when I programme the JW device the actual timing period is out by 10%. Is this what I should expect? Should I use delay timer rather than TMR0? TIA for any replies. z -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body