Abstract: A multi-port LAN switch is provided that enables attached network devices to both communicate directly and to insert into a token-ring network through an attached concentrator. Each port of the multi-port LAN switch has a first transformer, a second transformer, and a switching system. The first transformer has a first winding connected to a first connection of the port. The second transformer has a first winding connected to a second connection of the port. The switching system switches to a port mode or an adapter mode as a function of a mode signal transmitted to the port In the adapter mode, the switching system connects a second winding of the first transformer to a transmitter circuit in the port, and its connects a second winding of the second transformer to a receiver circuit in the port.

Abstract: A telephone interface protection circuit and modem incorporating the telephone interface protection circuit. The circuit includes a sensing circuit and a determining circuit. The interface protection circuit checks for an active telephone line and checks the line for over-current conditions caused when a modem designed for the public switched telephone network is plugged into a private digital telephone network. The circuit functions when the modem is operating to provide continuous monitoring. It can be built as a stand-alone device or incorporated into a modem. The circuit notifies the user of the line condition either with LEDs or with a status message sent to the user via the host computer interface.

Abstract: A multi-port LAN switch is provided that enables attached network devices to both communicate directly and to insert into a token-ring network through an attached concentrator. Each port of the multi-port LAN switch has a first transformer, a second transformer, and a switching system. The first transformer has a first winding connected to a first connection of the port. The second transformer has a first winding connected to a second connection of the port. The switching system switches to a port mode or an adapter mode as a function of a mode signal transmitted to the port. In the adapter mode, the switching system connects a second winding of the first transformer to a transmitter circuit in the port, and its connects a second winding of the second transformer to a receiver circuit in the port.