Hey Guys.
I want to start with ATSAMD21G18, so I build my own Devboard to get in contact with it. As a reference I use this schematic of Adafruit Industries
My Question is, the crystal oscillator of 32.768kHz for what is it used? I think it's for the built-in realtime clock, isn't it? So as I do not use the rtc I think I do not have to place it. Am I right?
Best regards
Hi @s-fr
Yes you're right, the main use of the external 32.768kHz crystal is to run the built-in real-time clock.
The alternative is to go crystal-less and use the on-chip internal 32.768kHz oscillator instead, however this is significantly less accurate and precise than the crystal. The decision to go crystal-less or not depends on whether your project requires some form of absolute (rather then just relative) timing.
To give you an idea, a typical 32.768kHz external crystal will give you a timing accurate to around ±1.7 seconds per day, whereas the using the internal 32.768kHz oscillator it could be up to ±20 minutes per day.
Note that on the Arduino based SAMD21 boards the 32.768kHz signal (crystal or crystal-less) is used as a clock source that's multiplied up by a digital frequency locked loop that generates the main 48MHz CPU clock. Therefore, if you're going crystal-less it will mean all of microcontroller's other internal TCC/TC timers will be less accurate as well. Again whether this is an issue will depend on your project.
thank you so much for this very detailed explanation
Best regards
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