Changing I2C reading mode

[Fin95]

Hi,

I am trying to create the I2C communication using the format used from the company seller of the device.
I have to follow these steps:

I2CReadFunciton ( uint8_t slAddr,

uint8_t* wrData, int wrLen,

uint8_t* rdData, int rdLen

1. Initiate the bus by issuing a START condition.

2. If there are bytes to write (wrLen > 0):

   • Address the target device with its slave address in write mode.
   • Transmit the wrLen bytes contained in wrData.
   • Without releasing the bus (i.e., do not send a STOP), issue a REPEATED START to transition into the read phase.

3. Begin the read phase:

   • Address the same device with its slave address in read mode.
   • Receive rdLen bytes, storing them sequentially into rdData.

4. Terminate the transaction with a STOP condition.

Key constraints:

• If a write phase occurs, it must be immediately followed by a repeated start—no STOP is allowed between the write and the subsequent read.
• The read always occurs after either the initial START (if no write) or the repeated START (if a write was performed).

My problem is how to not have the stop condition in the write function using the HAL functions.

[TDK · Accepted solution]

Please include your full chip part number in your posts.

What device are you interfacing with?

HAL_I2C_Mem_Read will issue a write then a read with a repeated-start condition. Perhaps use that or look there to see how it is done.

stm32f4xx-hal-driver/Src/stm32f4xx_hal_i2c.c at b0c13b119171025ac8e47d9028032fb7b7f6fd6d · STMicroelectronics/stm32f4xx-hal-driver

[Fin95]

Thanks for the answer!

It's a gas sensor, but it's form the coompetition of ST, so I prefer not to say which is.

I have already used it, but it didn't work because it can happen that in the write part the wrLen cab be bigger than 1 byte, so the HAL_I2C_Mem_Read doesn't work.

In principle, it can happen I need to write 3 bytes and read 5 bytes.

I found the HAL_I2C_Master_Seq_Transmit_IT, but I am not pretty sure how to use it.

Thans in advance for the help