Fault-tolerant communications controller system

The present invention relates to a system for controlling multiple communications lines, so that a computer system can operate with a single component failure. Two processors are used to control two communications controllers and each of the controllers control up to 15 line controllers. Each line controller has two ports and each port is connected to a communications controller thereby providing two communications paths toeach processor. Two power supplies are also used to provide single failure fault-tolerance. Additionally, the disclosure relates to providing a downloadable microprocessor board in combination with, but separate from, an interface board that is designed to meet various communication format specifications and the line controller comprises the two boards. The use of a single microprocessor board improves produceability, maintainability and diagnostic capabilities.