STM32C0 SDA signal on PC14

[rnicolas]

Hi,

I'm trying to configure pin PC14 to be used as SDA signal as it stated in the datasheets STM32C031C6 and STM32C031G4:

To configure the pin (and the the I2C) I am using:

void SDK_I2C_Init(SDK_I2C_HandleTypeDef *hi2c) {
  LL_I2C_InitTypeDef I2C_InitStruct = {0};
  LL_GPIO_InitTypeDef GPIO_InitStruct = {0};

  LL_RCC_SetI2CClockSource(LL_RCC_I2C1_CLKSOURCE_PCLK1);
  LL_IOP_GRP1_EnableClock(LL_IOP_GRP1_PERIPH_GPIOB);
  LL_IOP_GRP1_EnableClock(LL_IOP_GRP1_PERIPH_GPIOC);
  /**I2C1 GPIO Configuration
  PB8   ------> I2C1_SCL
  PC14   ------> I2C1_SDA
  */
  GPIO_InitStruct.Pin = LL_GPIO_PIN_8;
  GPIO_InitStruct.Mode = LL_GPIO_MODE_ALTERNATE;
  GPIO_InitStruct.Speed = LL_GPIO_SPEED_FREQ_HIGH;
  GPIO_InitStruct.OutputType = LL_GPIO_OUTPUT_OPENDRAIN;
  GPIO_InitStruct.Pull = LL_GPIO_PULL_UP;
  GPIO_InitStruct.Alternate = LL_GPIO_AF_6;
  LL_GPIO_Init(GPIOB, &GPIO_InitStruct);

  GPIO_InitStruct.Pin = LL_GPIO_PIN_14;
  GPIO_InitStruct.Mode = LL_GPIO_MODE_ALTERNATE;
  GPIO_InitStruct.Speed = LL_GPIO_SPEED_FREQ_HIGH;
  GPIO_InitStruct.OutputType = LL_GPIO_OUTPUT_OPENDRAIN;
  GPIO_InitStruct.Pull = LL_GPIO_PULL_UP;
  GPIO_InitStruct.Alternate = LL_GPIO_AF_14;
  LL_GPIO_Init(GPIOC, &GPIO_InitStruct);

  LL_APB1_GRP1_EnableClock(LL_APB1_GRP1_PERIPH_I2C1);

  I2C_InitStruct.PeripheralMode = LL_I2C_MODE_I2C;
  I2C_InitStruct.Timing = I2C_TIMING;
  I2C_InitStruct.AnalogFilter = LL_I2C_ANALOGFILTER_ENABLE;
  I2C_InitStruct.DigitalFilter = 2;
  I2C_InitStruct.OwnAddress1 = 180;
  I2C_InitStruct.TypeAcknowledge = LL_I2C_ACK;
  I2C_InitStruct.OwnAddrSize = LL_I2C_OWNADDRESS1_7BIT;
  LL_I2C_Init(I2C1, &I2C_InitStruct);
  LL_I2C_EnableAutoEndMode(I2C1);
  LL_I2C_SetOwnAddress2(I2C1, 0, LL_I2C_OWNADDRESS2_NOMASK);
  LL_I2C_DisableOwnAddress2(I2C1);
  LL_I2C_DisableGeneralCall(I2C1);
  LL_I2C_EnableClockStretching(I2C1);

  LL_I2C_Disable(I2C1);
  LL_I2C_SetTiming(I2C1, I2C_TIMING);
  LL_I2C_Enable(I2C1);
}

 which is almost the same code that we can find here.

If I configure another pin to work as SDA (PB9 or PB7) the system works perfectly and I can communicate using the I2C protocol.

Is there any configuration that I am missing for that specific pin?

[Andrew Neil]

What board are you running on?

Are you sure that there's no external hardware issues that would prevent PC14 to be used as SDA?

eg, is the pullup present on PC14?

Have you used an oscilloscope to see what, if anything, is happening externally on the pin?

[rnicolas]

For the most basic test I'm using the Nucleo-C031C6. The configuration is that one I already sent, and I see if I configure and connect other pins everything works fine, but not PC14. I'm doing the connection with jumper wires. There is nothing else connected between the two components. This setup does not include pull-ups and I rely on the internal pull-ups as described in the pin configuration

For the STM32C031G4 I'm using a propriertary board with 4k7 external pull-ups, and then configuring the pins with 

GPIO_InitStruct.Pull = LL_GPIO_PULL_NO;

lines are directly connected between the two components, no switching between boards, nothing.

In both cases, PC14 does not seem to work as SDA. 

[Andrew Neil]

Again, check that there's no external hardware issues that would prevent PC14 to be used as SDA.

I2C needs pullups - it won't work without them. Internal microcontroller pullups are seldom suitable.

See: https://community.st.com/t5/stm32-mcus-boards-and-hardware/i2c-between-two-nucleo-f446re-boards/m-p/769665/highlight/true#M23992

[Andrew Neil]

---

@Andrew Neil wrote:

Again, check that there's no external hardware issues that would prevent PC14 to be used as SDA.

---

eg, take look at the User Manual:

https://www.st.com/resource/en/user_manual/um2953-stm32-nucleo64-board-mb1717-stmicroelectronics.pdf#page=18

[KnarfB]

Scan the ref.man. RM0490 Rev 5 for PC14. Especially 4.7.6 FLASH option register (FLASH_OPTR) HSE_NOT_REMAPPED bit. Don't know if this applies to your case.

hth

KnarfB

[rnicolas]

This does not really apply in the second board that I described, I see from the schematics those are 0 ohm resistors that need to be placed and removed to actually access to PC14 on the pin header and disconnect the LSE. On my second board, there is literally a track that connects the two devices, and no LSE placed on that pin, so my question still stands.

[rnicolas]

Just checked, I see the value of FLASH_OPTR is 11111111111111111111111010101010, so I can see it is disabled, and still, there is no communication.