Abstract: A train communication and control system is described having the cars of the train connected by a two-wire train line running continuously from car to car. Each car has a transmitting circuit and a receiving circuit connected across the line. Any car may be selected to be a master unit. The selection of one car as a master unit disconnects the power sources of all other cars from the train line, leaving the master unit power source as the sole power source for the line. The master unit or any other car unit communicates with each other car by causing a high voltage ("mark" state or logic one) or a low voltage ("space" state or logic zero) to be on the train line. Each non-master car can receive a communication from a transmitting circuit, or can transmit to another car by applying a low impedance across the train line to change from a "mark" state to a "space" state. The power source consists of a voltage regulator with precision constant current limit.

Abstract: A train communication and control system is described having the cars of the train connected by a two-wire train line running continuously from car to car. Any car may be selected to be a master unit. The selection of one car as a master unit disconnects the power sources of all other cars from the train line, leaving the master unit power source as the sole power source for the line. The master unit communicates with each other car by causing a high voltage ("mark" state or logic one) or a low voltage ("space" state or logic zero) to be on the train line. Each non-master car can receive a communication from the master unit, or can transmit to another car by applying a low impendance across the train line to change from a "mark" state to a "space" state. The power source consists of a voltage regulator with precision constant current limit.

Abstract: A memory transfer unit is provided which permits replacing messages stored in a message display system with a different set of messages stored in the memory transfer unit. A circuit is provided for supplying power from the message display system to the memory transfer unit and for inhibiting operation of the memory transfer unit unless the power supply to it has a proper operating voltage level. Pulses produced in the message display system are counted to determine the sequential locations of data in the memory transfer unit to be transferred to the message display unit for substitution for data stored in the message display unit.