@6018.ADF Gateway Communications G/Ethernet Controller
3Com Drivers Page for David Systems Products (archived)
(Look for "6500/6501/6502" items, these seem to be relevant.)
Based on content by William R. Walsh (original HERE).
David Systems Ether-T Controller
F1,2,3,4 Blue potted parts
JP1 AUI or RJ45 select
LINK Unknown (set to "on" on my)
M1 Valor PT3785
P1 AUI connector
P2 RJ45 connector
U1 Ethernet Address
U3,4 Samsung KM62256ALP-10
U12 NS DP8390DN
U29 AT&T T7220PC
X1 20.000 MHz
3Com bought David Systems as far as I can tell. The official name for this particular adapter is "David Systems Ether-T Controller". It was actually manufactured by Gateway Communications for David Systems. The Gateway Communications version of the adapter is built a little differently but is functionally identical to this one. I don't know what became of Gateway Communications. The ADF above is for the David Systems variant.
What is the AT&T T7220PC used for? I see it on a quite a few older Ethernet adapters. Has anyone got a copy of the datasheet or other information regarding this IC?