HAL I2C Transmit then Receive without a stop between

[SnoZek]

Hello,

I’m using an STM32WBA65 and trying to communicate with a peripheral (PTX30W) over I2C1.

The peripheral requires the following I²C sequence:

START → WRITE → REPEATED START → READ → STOP

However, using HAL_I2C_Master_Transmit() followed by HAL_I2C_Master_Receive() does not work, because both HAL functions generate a STOP condition, and the PTX30W does not accept a STOP between the write and read phases.

On STM32WBA, I don’t see a HAL equivalent of HAL_I2C_Master_TransmitReceive() that would allow a repeated START without a STOP in between.

My questions are:

• Is there a way to achieve a WRITE + REPEATED START + READ sequence using the HAL on STM32WBA?

• Or is the correct approach to switch to the LL (Low Layer) I2C driver to get finer control over START/STOP conditions?

Any guidance or best practices for this use case would be appreciated.

Thanks in advance.

here is the i2c protocol :

[TDK]

Use HAL_I2C_Mem_Read to write 1-2 bytes, then read a bunch, using a repeated start.

[Andrew Neil]

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@TDK wrote:

Use HAL_I2C_Mem_Read to write 1-2 bytes, then read a bunch, using a repeated start.

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@Emil Damkjaer PETERSEN @Loic CHOSSAT this is particularly poorly described in the HAL documentation:

https://www.st.com/resource/en/user_manual/um3140-description-of-stm32wba-hal-and-lowlayer-drivers-stmicroelectronics.pdf#page=327

I really don't think it's at all clear from this description that "MEM" is the one to use in this application?

Please can we have a clear description like @TDK's in the HAL manuals - this kind of question comes up frequently on the forum!

I suspect that most applications where HAL_I2C_Mem_Read is the correct choice are not actually "memory" devices - as is the case here.

[TDK]

I think the HAL_I2C_Mem_Read naming is appropriate. Most uses of this are for actual memory addresses or register analogs. For example, accelerometers and other sensors, EEPROMs, LCD character displays. Just my opinion.