As shown in Figure 8-67, a single-byte data write transfer begins with the controller device transmitting a start condition followed by the I²C device address and the read/write bit. The read/write bit determines the direction of the data transfer. For a write-data transfer, the read/write bit must be set to 0. After receiving the correct I²C target address and the read/write bit, the device responds with an acknowledge bit (ACK). Next, the controller device transmits the register byte corresponding to the device internal register address being accessed. After receiving the register byte, the device again responds with an acknowledge bit (ACK). Then, the controller transmits the byte of data to be written to the specified register. When finished, the target device responds with an acknowledge bit (ACK). Finally, the controller device transmits a stop condition to complete the single-byte data write transfer.

Figure 8-67 I²C Single-Byte Write Transfer