Abstract: An expandable repeater controller for a local area network. The expandable repeater controller has with three expansion ports. An interface signal is transmitted through an EXPOUT port when the expandable repeater controller is going to transmit data through a DAT port. The interface signal is received through an EXPIN port if the expandable repeater controller is required to receive data through DAT port. The operational status of the expandable repeater controller is determined by logic levels of ports EXPOUT and EXPIN. The repeater controller of the invention is provided with an expansion port circuit which includes means for generating synchronous clock signals, means for dealing with data collision conditions and means for transmitting and receiving data as well as the interface signals. The repeater controller further includes an arbiter if more than two repeater controllers are connected for expansion.