Reading I2C bits with STM32F4Discovery

[BKem.1]

Hello. I have the following scheme for reading the output of humidity sensor that communicates via I2C:

How would I execute this sequence with STM32CubeMX IDE and HAL libraries? The output of the sensor is as follows:

All I have now is this code:

 

uint8_t buf[2]; // 2 bytes? how to get 14 bits?

while (1)

 {

 if (HAL_I2C_IsDeviceReady(&hi2c1, 78, 5, 10) == HAL_OK){

  res = HAL_I2C_Master_Transmit(&hi2c1, 78, 0, 2, 5); // start the writing cycle with bit 0;

  if (res == HAL_OK){

  res = HAL_I2C_Master_Receive(&hi2c1, 78, buf, 2, 10);

  if (res == HAL_OK){

  val = ((int16_t)buf[0] << 4) | (buf[1] >> 4); // how to combine these bytes?

   if ( val > 0x7FF ) {

       val |= 0xF000;

      }

  }

  }

  }

 HAL_Delay(100);

 }

[Tesla DeLorean]

val = ((int16_t)(buf[0] & 0x3F) << 8) | ((int16_t)buf[1] ); 

if (val & 0x2000) val |= 0xC000; // Sign Extend

[TDK]

Humidity can't be negative. I don't think the "sign extend" line is desired.

[BKem.1]

This seems to work, although the final measurement value is a bit off from what we have in the room. Could You explain, what You did with the first line of code? Thank You very much

[BKem.1]

Especially, where is the 0x3F byte from? What would happen, if I Would change its value?

[Piranha]

It should be noted that these separate write+read operations put stop-start bit sequence in the middle. HAL_I2C_Mem_Read() can do a complete sequence, but it works only with memory/register addresses. HAL has those "Seq" functions - probably you can cobble it together with that crap. But all of this is ridiculous for a "high-level" library...