PCA10040 v1.2.4 suitable clock accuracy

[MohamedElnaggar]

Hello All,

I am currently working with two boards of PCA10040

One of them is v1.1.1 and the other one is v1.2.4

My code must connect with other nrf52 boards to exchange data with it 

when flashing the code in v1.1.1 the two devices are connected correctly and exchange data and terminate connection correctly

and when burning the same code on the v1.2.4 they are connected correctly but the connection timeout fire, so there is no any data exchange

I searched for the problem and this link solved my problem https://devzone.nordicsemi.com/f/nordic-q-a/29786/ble_hci_connection_timeout-and-nrf_clock_lf_xtal_accuracy_xx_ppm

So using the NRF_CLOCK_LF_XTAL_ACCURACY_250_PPM instead of NRF_CLOCK_LF_XTAL_ACCURACY_20_PPM solved my problem 

My QUESTION is why this happened?? 

I tried to see the schematics of the version 1.2.4 but the site shows only the documentation until 1.2.1

So please, Can any one confirm that this is  a mandatory accuracy ? or this is just an issue in my board?

Thanks in advance

[Einar Thorsrud]

Hi,

All nRF52832 DK versions have a 20 ppm 32.768 kHz LF crystal. It might be that there is a problem with your DK. You can check the accuracy of the LFCLK for instance by using a RTC to toggle a GPIO via PPI and connect it to a frequency counter.

An alternative explanation could be if you have modified the example to use the internal RC oscillator instead? If so, this has a 500 ppm accuracy (instead of the specified 250 ppm due to erratum xxx). If you use a recent SDK you need to set the accuracy correctly when using the PPM. With older SDKs accuracy was always set high when using RC.