The profile of the chip looks like RAM, but check this out:
COM20020P
Category: Communication => Network => ArcNet/CAN
Description: Ulanc Universal Local Area Network Controller With 2k X 8 On-board RAM
Company: Standard Microsystems Corporation
Edit: DigiChip has the datasheet for the SMC chip.
This may be newer than the A560 ArcNet controller, but I would hazard to wager that it may have been an update to the A560. BBoAH says the A560 has a SANA-II driver and, "AS255r TCP/IP stack has built-in support," as does the A2060.
Now, this has mini-DIN and two RCA jacks, which appear much different than the coax/BNC connectors I have seen referenced for ArcNet. I did not get involved with networking (other than the huge token ring stuff on the System/34) until after Ethernet had been well established so I cannot make any historical reference from experience.