The Host Interface allows for complex interactions between an I2C controller and a PD Controller. The I2C Target unique address is used to receive or respond to Host Interface protocol commands. Figure 2-1 and Figure 2-2 show the write and read protocols, respectively. The Byte Count used during a register write can be longer than the number of bytes actually written. In other words, the controller can issue the stop bit without writing N bytes. Similarly, during a register read, the controller can issue the stop bit before reading all N bytes.

When writing a register that has a defined length of N bytes, if the I2C transaction only contains n bytes then the final (N - n) bytes of the register remain unchanged.

When reading a register that has a defined length of N bytes, the I2C controller may terminate the I2C read transaction after the first n bytes.