FIBER OPTIC COMMUNICATION OF THREE-LEVEL ELECTRONIC SIGNALS

摘要

A fiber optic extender system (Fig. 6) is disclosed in which messages are transferred by fiber optic lines between remotely located electronic units. The electronic units (e.g., transformer-isolated) have three signal levels: positive voltage, negative voltage, and zero voltage (Fig. 13). Because the fiber optic system can conveniently handle only two signal levels -on and off- potentially serious communication problems are avoided by generating and transmitting a short end-of-message pulse (282) whenever the transmitting electronic unit is at zero voltage level. This end-of-message pulse (282) is detected at the remote electronic unit, and the line is cleared for the next message.