Robust protocol for sending synchronisation pulse and RS-232 communication over single low quality twisted pair cable

This paper describes a protocol designed and implemented for use in a marine application. It provides robust multi-channel bidirectional communication over a single low-quality shielded twisted pair cable that is generally used for power, rather than communication. In addition, line continuity is not guaranteed. The system also transmits a time-critical synchronisation pulse over the same twisted pair. The protocol is quick and easy to implement on inexpensive hardware. Each side of the communication system makes use of a standard RS-485 driver and a Microchip PIC micro-controller. Laboratory-based test results are presented.