Abstract: A set of operating parameters that define the functions of a data unit interfacing a subscriber's terminal to a 2-wire telephone loop and which are stored in a volatile memory of a microcomputer in the data unit may be changed or periodically refreshed from the same parameter set stored in a volatile memory of a microcomputer in a data line card that functions as a datapath interface of a central data and voice communication facility. Bidirectional data transmission on the loop occurs via time compression multiplexing which requires synchronization between the interfaces. Loss of synchronization indicates the likelihood of a power interruption at the data unit and consequent erasure of memory. The presence of synchronization is tested and upon a positive indication the operating parameters are downloaded from the data line card to the data unit.