Problems after switching to new MCU STM32U0-Series

[SamLue]

Hi,

i developed my application with a dev-board STM32F103CB (Bluepill).

Here some facts:
Dev Environment: VS Code + platformio
framework = arduino
platform = ststm32
Hardware: STM32F103CB + sx1262
PINs:
NSS PA4
DIO1 PB12
RESET PB13
BUSY PA8

Everything with RadioLib and the LoRa Communication was fine. I could send Messages to my base station.

I have designed a PCB now with an other MCU. It is also a STM32, but from the newer low energy STM32U0-Series.

After solving some other Problems (e.g. defining i2c PINs) I sill have problems with the communication with my radio chip sx1262.

After checking everything, I found the first issue on my site. I switched NSS and BUSY in PCB design. So I fixed it in Software and File loraWanConfig.h with:

SX1262 radio = new Module(PA8, PB12 , PB13, PA4);

But still no communication. After I enabled debugging, the log says that RadioLib can not find the Module:

Initialise the radio
RLB_DBG: 
RadioLib Info
Version:  "7.1.2.0"
Platform: "Arduino STM32 (official)"
Compiled: "May  7 2025" "18:43:53"
RLB_DBG: SX126x not found! (1 of 10 tries) RADIOLIB_SX126X_REG_VERSION_STRING:
RLB_DBG: 00000320: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff  ................
RLB_DBG: Expected string: SX1261

I found some difference between the STM32F103 und the STM32U0 in the PIN Definition-Files for stm32duino.

Here the Part for STM32F103:

#ifndef PIN_SPI_MOSI
  #define PIN_SPI_MOSI          PA7
#endif
#ifndef PIN_SPI_MISO
  #define PIN_SPI_MISO          PA6
#endif
#ifndef PIN_SPI_SCK
  #define PIN_SPI_SCK           PA5
#endif

And here for STM32U0:

#ifndef PIN_SPI_MOSI
  #define PIN_SPI_MOSI          PA7
#endif
#ifndef PIN_SPI_MISO
  #define PIN_SPI_MISO          PA6
#endif
#ifndef PIN_SPI_SCK
  #define PIN_SPI_SCK           PA1
#endif

I checked the official STM Datasheet. And there I can find in the STM32U073x8/B/C pin/ball definition Table for PIN Name
PA5 SPI1_SCK
PA6 SPI1_MISO
PA7 SPI1_MOS

And thats exact how the sx1262 is wired to the mcu. So I tried to redifine the PINs, but without success.

I tried it with:

    SPI.setMISO(PA6);
    SPI.setMOSI(PA7);
    SPI.setSCLK(PA5);
    SPI.begin();

and

#define PIN_SPI_SCK PA5

and also like it is described in the RadioLib Documentation.

  SPIClass NewSPI(PA7, PA6, PA5);
  SX1262 radio = new Module(PA8, PB12 , PB13, PA4, NewSPI);

But the debug message "RLB_DBG: SX126x not found!" stays.

Has someone an idea to get this up and running?

[jgromes]

It would help us a lot to see your complete initialization. In the last example, you still need to call newSPI.begin() before radio.begin().
In general, the radio seems to only return 0xFF bytes, which is characteristic of incorrect SPI wiring/setup or the radio being unpowered.

[SamLue]

Thank you!
With this information I could determine the problems.
Because of the wrong PIN Defintion I had to define newSPI and I forgot the newSPI.begin() - Thanks for this hint.
And I also found a wiring-issue in my PCB-Design.