You know I wondered about this too. It is particularly odd considering that the circuit shown implements nothing but a 16 bit output / input scheme. Due to how it works it is not possible to use the circuit in conjunction with other standard I²C devices. In addition to that, this circuit strays from any semblance of I²C standards because it does not implement addressing and the R/W bit nor is it provisioned with the 9^th bit ACK pulses.

When one realizes this you see that there is literally no advantage to this circuit over an SPI type scheme. Some may have thought, "Oh I can use my existing I²C bit bang driver software", but due to the non standard (a.k.a. non existant protocol) not even that is feasible.

Michael Karas