Hi Bruno,

You don't say whether you are looking for hardware or software I2C routines. I don't know if the '420 has hardware I2C built in, and don't have time to look it up.

Doing software I2C for master by bit-banging is easy, there is example software available, check for apnotes at various vendor websites; I know Atmel has it.

Doing software I2C for slave I wouldn't bother with unless you have a FAST uC and can settle for SLOW I2C.

Dennis