I²C on STM32C011 using PC14 (SDA) not working

[jack_daniels]

Hello,

I am working on an STM32C011 (Nucleo-like custom board) and trying to use I2C1 with the following pinout:

• PB7 → I2C1_SCL (AF14)

• PC14 → I2C1_SDA (AF14)

According to the reference manual / datasheet, PC14 can be mapped as I2C1_SDA (AF14).
I connected an SHTC3 humidity/temperature sensor (address 0x70) to these lines with 4.7k pull-ups.

Problem:

• My I²C scanner code never detects the SHTC3 (always NACK at 0x70).

• If I configure I²C on PB6/PB7 instead, the scanner works.

• GPIO PC14 seems not to toggle as SDA when I try transactions.

I suspect this might be related to PC14 also being used for LSE (OSC32_IN). In CubeMX, I set LSE = Disabled under RCC.
But I still wonder if PC14 can reliably be used for I²C, or if there are silicon limitations when LSE is involved.

Questions:

1. Is PC14 fully usable as I²C SDA on STM32C0 when LSE is disabled?

2. Has anyone successfully used I²C1 on PB7 (SCL) + PC14 (SDA)?

3. Could this be a hardware limitation / errata, or am I missing a CubeMX clock configuration detail?

Any feedback or working examples would be greatly appreciated 

[TDK]

Configure PC14 as a GPIO output and toggle it. Do you see the signal on a scope?

 

[jack_daniels]

Yes if PC14 configured as GPIO output and if it is toggled , i see the signal

[Andrew Neil]

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@jack_daniels wrote:

custom board 

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So please show your schematic

How to write your question to maximize your chances to find a solution

[STOne-32]

Dear @jack_daniels ,

Can you please share the Firmware code generated for the AF14 selection and the Ports Clock Activation ( C and B)  .  it might be an issue on the Code Generation .  Go to file stm32c0xx-hal_msp.c to check it ?

Thank you

STOne-32.

[WZHaha]

If you configure PC14 using cubemx, you will find that its speed can only be set to low speed. Perhaps this is because your clock speed is not high enough or the resistance value of the pull-up resistor is too high, causing the level to not flip in time. In the Errata Sheet ES0569, you can also find the problem with IIC SDA, which might be related to the issue you raised.