I'm using an AT24MAC602 serial EEPROM with a built in factory programmed by Atmel EUI-64. Unfortunately the application needs IPv4 not IPv6 so I need to down-convert the 64-bit EUI to a 48-bit one. How is it done?
Up-converting is easy. Take the first 24-bits of the 48-bit EUI from the AT24MAC402, insert 0xfffe or 0xffff, and append the last 24-bits of the 48-bit EUI. Now it's a 64-bit EUI. The Atmel Xplained boards are the AT24MAC402 48-bit chip.
What about the reverse with Atmel's AT24MAC602? Obviously if the middle bytes are 0xfffe or 0xffff just chop them out and concatenate. Unfortunately the ATMAC602 chips I have are returning 0x0000 in the middle bytes. If I just chop them out is the shorter 48-bit EUI still globally unique?