TMR1 & Button - long delay (1 min) before starting

[HenrikOlsson]

Define "best".
Accuracy, long time stability, resolution, power consumption, ease of use, what?

You can either run the PIC off of an external 4MHz (or whatever you need) x-tal and derive the TMR timebase from the main oscillator. You won't get as slow as 1Hz but you can get, lets say, 100Hz and keep counting interrupts. Or you can use the TMR1 oscillator with a separate (32768Hz ) x-tal. Since it's a 16bit timer it will overflow every 2 seconds if you let it freerun.

/Henrik.

[flotulopex]

When timing is in the game, for me "best" is "accurate".

Does a higher crystal frequency mean more accuracy?

Is it best to choose 4'194'304MHz (32'768kHz*128) crystal and lots of interrupts (if used) or a 32'768kHz one (less interrupts - plenty of time to do "things")?

[HenrikOlsson]

Doesn't really matter as far accuracy goes. Look at the frequency tolerance of the crystals you're considering, the one with the lowest value will be the most accurate one. But keep in mind that the TMR1 oscillator is designed specifically for low frequency crystals, typically a 32.768kHz. The datasheet for the 16F690 says DC to 200kHz.

/Henrik.

[flotulopex]

Thanks a lot, Henrik.