Is a 32.768 kHz crystal external to the module required?|FAQ|ROHM Semiconductor

FAQ's

Is a 32.768 kHz crystal external to the module required?
- No. It is not required.
  Since MK71511/MK71521 feature a built-in 32.768 kHz crystal oscillator, no external crystal is required. Although MK71511A/MK71521A do not contain the 32.768 kHz crystal oscillator, the RC oscillator of the on-board SoC (nRF52811/nRF52832) and the like can be used. Note that the frequency deviation when using the built-in RC oscillator is ± 2%, and periodic calibration is required to ensure the frequency deviation of ± 250 ppm.