To write on the I²C bus, the controller sends a START condition on the bus with the address of the target, as well as the last bit (the R/ W bit) set to 0, which signifies a write. The target acknowledges, letting the controller know it is ready. After this, the controller starts sending the control register data to the target until the controller has sent all the data necessary (which is sometimes only a single byte), and the controller terminates the transmission with a STOP condition.

There is no limit to the number of bytes sent, but the last byte sent is what is in the register.

Figure 8-4 shows an example of writing a single byte to a target register.

Figure 8-4 Write to Register