STM32 Scan I²C bus

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Scanning an I2C bus using HAL is really simple. First configure I²C in STM32CubeMX:

I2c Config.png

Once the I²C has been configured, scanning the bus for slaves become a simple matter:

// Go through all possible i2c addresses
  for (uint8_t i = 0; i < 128; i++) {

	  if (HAL_I2C_IsDeviceReady(&hi2c1, (uint16_t)(i<<1), 3, 5) == HAL_OK) {
		  // We got an ack
		  printf("%2x ", i);
	  } else {
		  printf("-- ");
	  }

	  if (i > 0 && (i + 1) % 16 == 0) printf("\n");

  }

  printf("\n");

The HAL_I2C_IsDeviceReady will return HAL_OK if it receives an ACK or an error if not.

With a DFRobot 10 DOF hooked up to the I²C bus, the output from above could be:

-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
-- -- -- -- -- -- -- -- -- -- -- -- -- -- 1e -- 
-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
-- -- -- 53 -- -- -- -- -- -- -- -- -- -- -- -- 
-- -- -- -- -- -- -- -- 68 -- -- -- -- -- -- -- 
-- -- -- -- -- -- -- 77 -- -- -- -- -- -- -- -- 

Notice that I²C addresses are a bit peculiar.

I²C 7-bit Addresses.png

The address itself is shifted 1 bit left and the last (LSB) bit indicates read or write.

If, for example, we look at the ITG-3200, the datasheet states the following:

ITG-3200 I2C address.png

Binary 01101000 = 0x68, so the 68 in the above output is this particular sensor. However, the HAL_I2C functions will expect the address shifted left:

0x68<<1