Thanks for the reply.

I have some projects where the inputs are optoisolated, outputs are relays and analog drive directly the PIC inputs through some sort of zener diode protection.

For the digital part I use the Parallel input-Serial Output and the reverse, Serial Input-Parallel Output registers like the 4021 and 4094 or the A6841/MIC6841 that drives relays directly. Especially the latter is a good IC and drives relays with no need for other components. I wonder if there is an equivalent in I2C.

This registers need at least 5 lines for data-in, data-out, clock, strobe and load. That is why I think to jump into I2C.

Regards,
Ioannis