RTC Setting of Nrf51822

[BK]

Hi, I'm using Nrf51822 to implement a RTC(200ms tick) I connect a external 16MHz crystal to the MCU. I use the S110 softdevice with BLE function enabled, so it's in ble_stack_init() where to setup the crystal, right?

My question is which crystal option should I select? (below table)

I once tried to use NRF_CLOCK_LFCLKSRC_XTAL_20_PPM, but I found that it seems a coule of seconds faster than the real time after a couple of hours...

Or am I suppose to use NRF_CLOCK_LFCLKSRC_SYNTH_250_PPM?

[Jørn]

Hello BK

When the 32.768 kHz crystal is not present you can choose between two low frequency clock sources. Either the internal RC oscillator, or a synthesized low frequency clock created from the high frequency clock. Do note that the synthesized clock has a higher current consumption, and the high frequency clock must be running at all times. You can read more about these choices here.

Best regards

Jørn Frøysa