Is there no CCP module on this PIC where you can use the "compare" function? That will create the interrupt and you can update the compare value with the number of ticks to the next compare. Leave Timer1 freerunning. Regards, Gordon Williams ----- Original Message ----- From: "Mark Rages" To: "Microcontroller discussion list - Public." Sent: Wednesday, May 21, 2008 7:59 PM Subject: Re: [PIC]: 32.768Hz operation : On Wed, May 21, 2008 at 6:48 PM, Rolf wrote: : > The simplest thing is to set the most significant bit of the TMR1H byte : > very soon after the TMR1 interrupt.... (to be absolutely safe, it must : > be within 256 ticks of TMR1 or 7.8ms). : > : > bsf TMR1H,7 : > : > What this does is cause the interrupt to happen in exactly 1 time per : > second .... ;-) : : Good idea (update only the high byte, let the low one run) but it won't work. : : >From the datasheet: : : The Timer1 high byte is updated with the contents of TMR1H when a : write occurs to TMR1L. : : Regards, : Mark : markrages@gamil : -- : Mark Rages, Engineer : Midwest Telecine LLC : markrages@midwesttelecine.com : -- : http://www.piclist.com PIC/SX FAQ & list archive : View/change your membership options at : http://mailman.mit.edu/mailman/listinfo/piclist : -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist