Safe temperature range for nRF52840 - nRF9160 UART 115200 without external crystals for HF clocks

[Michal Mühlpachr]

Hi,

what is safe temperature range for nRF52840 - nRF9160 UART communication on 115200 baudrate without external crystals for HF clocks please ?

Thank you.

[Simonr]

Hi

As long as the other components you're using supports these temperatures the nRF52840 and nRF9160 are both able to operate safely from -40°C to 85°C.

Best regards,

Simon

[Michal Mühlpachr]

Hi,

thank you, that is clear.

But we need to now, whether UART clocked from internal RC (without external crystal) in both chips will not mismatch each other to inject bit errors between TX and RX on 115200 baudrate 8N1 in whole temperature operating range from -40°C to 85°C.

Regards,

Michal

[Simonr]

Hi

As stated in the UART peripheral chapter of the product specification of both the nRF52840 and nRF9160: The external crystal oscillator must be enabled to obtain sufficient clock accuracy for stable communictation. So no, the UART clocked from the internal RC oscillator will not be sufficient to ensure stable UART communication at any temperature. The RC oscillator also uses the external HF clock to calibrate and is prone to temperature changes, so this would be a bad idea.

Best regards,

Simon

[Michal Mühlpachr]

Thank you. Why then in Serial LTE modem is CONFIG_SLM_EXTERNAL_XTAL=n as default ?

[Simonr]

Hi

This config was temporarily disabled for current consumption reasons in a previous release, and has not yet been resolved. We are currently working on a fix to enable the XTAL while the current consumption stays at the desired level. We have not seen any issues with UART instability while this config has been disabled, but we can't guarantee stable communication I'm afraid.

Best regards,

Simon