How to calculate the oscillator limiting resistor

[federico.massimi]

Hi, I need some help with designing an oscillator for an STM32, I have some questions:

1.      I use the 32KHz oscillator only for the watchdog, so I don't need much precision, but is it still necessary or advisable to use an external crystal or is there no big difference compared to the internal oscillator? If the answer is that it is necessary, the second question also covers this.

2.      As for the HSE oscillator, I think it makes sense to use an external oscillator, but I haven't figured out how to calculate the limiting resistor to put in series. This:

 I've read the application note, but it talks about using probes to make measurements, I would like to understand how to calculate this resistance or if there are standard values to use. I have seen that often it is not put at all, other times a resistance in the order of 100 ohms is added.

For now I have select these two crystals: 830108288709 and an ECS-.327-12.5-34QS-TR, but I don't know if they are suitable for STM32 MCU.

Do you have any part number to recommend for which the value of the series resistor is well known.

PS: my micro is an STM32L476

[AScha.3]

so....