UART heat problem

[Astalos]

Hi I have working module which communicates via uart with another module. It works good, unless it is heated to 40C. After that temperature UART communication is not correct, there are framing errors etc. What might be wrong with temperature there? Is it something about hardware?

[Turbo J]

Did you check the UART data lines with an oscilloscope?

[Turbo J]

Try using the HFCLK crystal oscillator - the quarz is much more stable across the temperature range.

You can use the sd_clock_hfclk_request() softdevice call or NRF_CLOCK->TASKS_HFCLKSTART=1; if you don't use a softdevice.

[Astalos]

Does it mean that I should provide some external cristal oscillator? Or this is just swicthing some internal oscillator mode?

[Turbo J]

The correct crystal must be present for BLE to work at all - so it will be there in case you used any kind of OEM module. Note that the NRF51x defauls to the internal (R/C?) oscillator which is less precise but also uses less run current.