I'm trying to get a 32768 crystal to drive the RTC module for the QE128 while getting regular interrupts about every ms.
Right now, I have things working correctly using the internal oscillator, but I'd like to improve long term RTC accuracy.
First of all, is this even possible? When I set the prescale value to 0, it appears to disable the RTC clock source (the interrupt vector never runs). So given that it appears I HAVE to use the prescaler, it's not possible for me to set the prescaler to a low value when using an external clock source.
Second, while I'm certain that the crystal and trim capacitors are installed correctly, I cannot get the RTC to use this crystal with any prescale value. Does anyone have any suggestions?