Hello Everyone, I am trying to interface MLX90614 sensor I2C with stm32F401 Discovery board and i have configured stm32 cube MX in standard mode. My sensor works fine and I am using logic analyser to analyse my SCL and SDA signals.

[APand.7]

However, I am getting 0x3A(NACK) in stop condition of my logic analyser. Can anyone help me how i can convert this NACK to ACK. I am attaching my code snippet and my logic analyser signal as well . Thanks for help and support.

uint8_t I2C_ADDRESS = 0x00;

int main (void)

{

HAL_StatusTypeDef status = HAL_ERROR;

uint8_t buf[3] = {0,};

uint32_t temp_data_a;

uint32_t temp_data_o;

__IO float T;

__IO float To;

 status = HAL_I2C_IsDeviceReady(&hi2c1, I2C_ADDRESS, 3, 1000);

while(1)

{

HAL_I2C_Mem_Read(&hi2c1, 0x00, 0x06, 1, buf, 2, 1000); // Read Ambient temperature from Register 0x06

 temp_data_a = buf[1]*256 + buf[0];

 HAL_I2C_Mem_Read(&hi2c1, 0x00, 0x07, 1, buf, 2, 1000); // Read Object temperature from Register 0x07

 temp_data_o = buf[1]*256 + buf[0];

 To = temp_data_o*0.02;

 if(To >= 273.15)

  {

  To = To - 273.15;

  }

  else

  {

  To = -(273.15 - To);

  }

 T = temp_data_a*0.02;

if(T >= 273.15)

{

T = T - 273.15;

}

else

{

T = -(273.15 - T);

}

 HAL_Delay(500);

}

[Foued_KH · Accepted solution]

Hello @APand.7​ ,

The 0x3A means the value of the PEC according to the datasheet.

" The MLX90614 returns PEC after 16 bits data of which only 4 are meaningful and if the

MD wants it, it can stop the communication after the first byte. "

Foued

[APand.7]

Good Morning Foued

Thanks for your help. I do not want to stop the communication and I am more like a beginner, can you please help how i can do this and get ACK with 0x3A.

i want ACK with 0x3A, can you please suggest what should i do.

Thanks for your help and support

[APand.7]

i have simulated this project using SMBUS and I got this siganls.

I want to achieve the same signals.

Can you please help. How i can get the same signals in I2C.

[APand.7]

Hello Foued

Thanks for your reply. Sorry I misinterpret your answer. Actually 0x3A is error code.

Can you please look at my code and please tell me what i need to modify to get ACK

Sincerely Yours

Ashwani Pandey

[Piranha]

Why did you create a duplicate topic? It is forbidden! And why the code is not in a Code Snippet?

Read the I2C specification and you will understand why there is a NACK on the last byte.