Abstract: A modem enabling multi-point networks to be established over power lines emulating the RS-485 electrical interface standard for data transmissions. The modem includes a data terminal interface unit for exchanging data with a data terminal, a power line interface unit for placing data onto and taking data off of the power line, and a parallel I/O interface connecting the two units and including a network processor implementing a network protocol for sending and receiving messages. The parallel I/O interface provides for very fast data transfers across the parallel I/O interface compared with the rates at which the modem receives data from the power line and from the data terminal. In addition, at least the outgoing data is transferred across the parallel I/O interface in a form intermediate between the serial RS-485 data stream from the data terminal and the message packet that is sent over the power line by the power line interface unit.