The system requirements of the physical layer of a star-connected local area network (StarLAN) are examined. The network forms a 1-Mb/s component of the IEEE 802.3 CSMA/CD (carrier-sense multiple-access with collision detection) system. The new standard allows CSMA/CD network protocols to be used over telephone twisted pairs for office or industrial digital communications. The use of this protocol means that existing local area network controllers and their higher level operations will be immediately compatible with StarLAN operation. The philosophy and functionality of the AM7961 StarLAN coded data transceiver is discussed in the context of the StarLAN environment and multipoint extension (MPE), a bus-oriented extension. MPE is a demanding requirement which needs special consideration in the collision detection system used by the chip. It is graphically shown why these requirements cannot easily be met by conventional techniques. The results on the test demonstrate that the overvoltage sensing system used in the chip overcomes the difficulties encountered.>