Timer1 32.768KHz and INTRC_IO

[ljbeng]

Following along the lines of the TIMER LATENCY post by darrepac....

I have a 16F628 using the internal rc oscillator and I want to make Timer1 increment from a 32.768KHz crystal. I use the Timer1 interrupt to increment a real time clock. Since timer 1 would take 2 seconds to overflow, I set timer 1 to 0x8000 at the top of the interrupt, then I increment the time value (sec, min, hour).

What kind of latency should I expect?

The registers are being written from the internal rc of ~4MHz. Timer1 is incremented off the 32.768KHz crystal. Won't the registers be reset a lot faster than the 32.768KHz crystal can increment? My first tests show a reload of 0x8000 is too slow and looses time over a few hours.

[Mark]