20.5.4.3.4 7-Bit Address and Client Write with the AHEN and DHEN Bits
The client device reception, with the AHEN and DHEN bits set, operates
with extra interrupts and clock stretching added after the eighth falling edge of SCLx.
These additional interrupts allow the client software to decide whether it wants to
ACK the receive address or data byte rather than the hardware.
Note: The I2CxIF interrupt is still set after
the ninth falling edge of the SCLx clock, even if there is no clock stretching and the
RBF bit has been cleared. The I2CxIF interrupt is not asserted if a NACK is sent to the
host.