My two don't. It was a feature Apple made a fairly big deal about in the early days of LocalTalk; but I think once Ethernet became the obvious successor, Apple stopped bothering with LocalTalk. Which is funny, because you'd think that would be EXACTLY when the external-clock feature would be most useful! After all, LocalTalk's externally-clocked maximum was 2 Mbps, which happens to be the same speed as coax Ethernet. That would seem to be a perfect pairing for LocalTalk-to-Ethernet adapters.