NRF51822 UART speed 115200 is inaccurate

[VadimSavchuk]

Hello. I tried to use UART speed 115200. But my slave does not response. I connected slave to the arduino and it is working corectly. I got 2 oscillograms . From arduino and from NRF51. And I have seen that signal from NRF51 is inaccurate.

bellow is oscillogram from arduino

and from nrf51

How to encrease accurate for NRF51? Thank you in advance

[Turbo J]

Turn on the crystal oscillator.

[VadimSavchuk]

thank you for your answer. I use ble nano board from “red bear”. On this board I have 32.768 KHz crystal. And I use softdevise. When I config ble stack I use NRF_CLOCK_LFCLKSRC_XTAL_20_PPM define. If I undersood corectly already I have turned on external crystall

[run_ar]

The uart clock is derived from the High frequency clock. Did you also turn on the High frequency crystal?