Abstract: An interface system having a single detector to detect incoming signalling including ringing, tip ground, forward loop current, and reverse loop current. Relays and bias control are utilized to perform outgoing signalling and for configuring the system to defect the various incoming signalling states with a single detector.

Abstract: A high-speed digital transceiver is provided for use in a PBX environment comprising twisted-pair wire cables interconnecting like transceivers, each transceiver being operative to exchange voice, data and control information in a packetized format over a common twisted-pair cable. Specifically, each transceiver communicates packetized pulse code modulated information in pure Alternate Mark Inverted (AMI) coding, that is, without the introduction of bipolar violation pulses to provide timing. Frame synchronization is acquired on the first pulse by the use of a digital circuit deriving synchronization from a local high-speed clock. The use of a high-speed clock-driven digital circuit for synchronization acquisition eliminates the need for a phase-locked loop synchronization scheme and its concomitant finite acquisition delay.

Abstract: A system for connecting printed circuit boards to card cages. In addition to a conventional pin-and-socket connector arrangement for making signal and main power connections, the printed circuit board has a conducting pad coupled to the power traces of the board. A clip mounted in the card cage and connected to a first power source isolated from the main power source engages the pad before the conventional connectors make contact. Thus, the board is powered up first. As the board is fully seated and the conventional power and signal connections made, the power clip slides off the pad to break contact, leaving the main power source supplying power to the board.