I'm late to this party, but with regard to the DEC DE500 PCI 
EtherFast NICs, there were three models, in this chronological order:

	DE500-XA	21140
	DE500-AA	21140
	DE500-BA	21143

The precise model can be told from the FCC ID silkscreened on the 
PCB. The XA does not support Nway autonegotiation; the AA and BA do.

In my experience with Alphas, the AA is the one you want if you want 
to reliably netboot an Alpha on a modern 10/100 switch with auto 
negotiation; the SRM support for the 21143 came late enough in the 
game that not all systems got those revs (e.g. PC164).

	Erik <fair@netbsd.org>