Cannot run at -20 degree C for Murata CMWX1ZZABZ-078 Lora module and I-CUBE-LRWAN firmware.

[Steve5]

Hi,

We are using Murata CMWX1ZZABZ-078 Lora module and I-CUBE-LRWAN firmware for our IOT project development. There is another host ( STM32) MCU sending AT command at 115200 baud rate to control murata lora module and it works fine at room temperature. But when we test at -20 degree C temperature, the Lora module cannot respond correctly. We capture the uart waveform from Lora module and find that the baud rate look like at very high speed.

Since the setting of STM32L MCU inside murata module is using internal RC oscillator, will it be problem at -20 degree temperature? Do you have any recommendation of setting at very low temperature?

Regards

[Peter BENSCH]

Welcome, @nonesuchi​, to the community!

The internal RC oscillator is only suitable for communication with UARTs within a limited temperature range, as its tolerance becomes too great at temperatures below -10°C (see data sheet, table 44).

I don't have detailed documentation of the CMWX1ZZABZ-078, but the TCXO is probably only used by the included SX1276 and is not available for the STM32 as a clock, right?

Maybe you should switch from control by UART to synchronous transmission with e.g. SPI, where the clock accuracy is negligible?

Regards

/Peter

[Steve5]

Hi Peter,
Thanks for your prompt response. Enclosed, pls find the datasheet of the murata module. and there is any option to connect TCXO to STM32L PH0_OSC_IN externally. When it is working for Sigfox, it is suggested to connect these signals externally.
But for Lora, the reference design is using internal RC, is there any reference to use external TCXO so to have accurate clock?
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Regards
Steve Li

[Peter BENSCH]

Unfortunately, you have not inserted the pictures in such a way that they can be seen here. However, I can't say much about the Murata module - despite the STM32L082 it contains, the module is not an ST product.

If no one here in the community has experience with it, maybe there is help in the Murata forum?

Good luck!

Regards

/Peter

[Tesla DeLorean]

The DISCO board provides a solder bridge to get the crystal clock. Probably need to check the build options in the code. The plumbing and TCXO power should be the same as SigFox.

Don't use email methods to respond to forum posts, don't recall images and attachments working.