Network interface units and communication system using network interface

Abstract

A network interface unit couples a lattice communication network and at least one token ring network. The network interface unit includes a sequence controller which controls a token detector and a reception register so that message information received from the lattice communication network via a node apparatus connection port is looped back from the token ring network via a terminal connection port and output from the node apparatus connection port when an address detector detects that a destination address matches a stored source address, and absorbed when the address detector detects that the destination address does not match the stored source address. The network interface unit also includes a phantom signal part which outputs a detection signal via the terminal connection port when a phantom signal has been received, the phantom signal part including a set of resistors coupled to the terminal connection port, each of the resistors having a resistance that produces a detection signal having an appropriate level.