Abstract: A technique for converting a sequence of binary digits into a sequence of signalling alphabets of a modulated carrier signal for data transmission. By differentially encoding incoming data, non-linearly encoding the differentially encoded output in a state-dependent sequential manner and mapping the non-linearly encoded output into an expanded set of signalling alphabets having 90, 180 and 270 degree phase ambiguities, enlarged minimum Euclidean distance between possible sequences of signalling alphabets is achieved while the effect of the phase ambiguities of the expanded set of signalling alphabets can be removed in the receiver. This results in a reduced error probability when maximum likelihood decoding and differential decoding are applied in the receiver.

Abstract: A frequency and phase comparator circuit for determining the frequency difference between a reference signal of a known frequency and a variable signal of unknown frequency. The subject circuit monitors the two signals and detects the occurrence of phase shifts between the two signals. In particular, this circuit detects phase shifts of 180 degrees and 360 degrees and records a full slip indication with each occurrence of a 360 degree phase shift. These phase shifts indicate that at some point in time during transmission, the two signals were out of phase and not of exact frequency. In addition, the subject circuit provides a direction of drift indication with each 180 degree shift. These direction indications are output following a 360 degree phase shift or full slip and are determinative of the relative frequencies of the two signals by designating whether the frequency of the variable signal is higher or lower than that of the reference signal over the duration of the full slip.

Abstract: There is disclosed a control channel interface circuit for interfacing a port processor of a distributed multiprocessor communication system to a common time division multiplexed bus. The detection, extraction and synchronization of control messages passed between a central processor and port processor via a TDM bus are handled by the interface unit thereby relieving a port processor of this burden. A group of control time slots within a system frame are dedicated for the transfer of control messages between port processors and a central processor. The interface unit also monitors the operability of a respective port processor and automatically disables a faulty processor.

Abstract: There is disclosed a processor controlled digital communication device which accepts message commands from a communication system as part of a communication protocol. These command messages are stripped from the protocol and combined within the communication device to control signaling thereat. Multi-bit time separated information (I) fields are used together with a single bit signaling (S) field. The S field bits are compiled over several frames to become the command messages.

Abstract: There is disclosed a digital telephone having dual voice and data handling capability over a single communication line. Time separated information channels are used to transport the voice and data information between the terminal and the main processor. A separate signaling channel is shared between the two information channels and information on the signaling channel is accumulated for distribution to either the voice device or the data device in accordance with address information contained within the accumulated signaling channel message.

Abstract: In the disclosed coded telephone ringing signal method and circuitry, audibly distinguishable ringing codes are generated by alternately shifting between at least a pair of single frequency tones at different modulation rates. Other distinguishable ringing codes are generated by changing both the modulation rates and tone frequencies utilized.

Abstract: There is disclosed a speakerphone circuit employing precision peak detectors in which the processing of talk down signals and switch guard signals is partitioned in order to accurately control complementary switched gain in the transmit and receive channels to achieve improved sensitivity to talk down switching action by setting a low switching threshold.

Abstract: A technique for converting a sequence of binary digits into a sequence of signalling alphabets of a modulated carrier signal for data transmission. By introducing additional redundant signalling alphabets and differentially coding incoming data in a state-dependent sequential manner, enlarged minimum Euclidean distance between possible sequences of signaling alphabets is achieved while phase ambiguity of the expanded set of signalling alphabets is removed. This results in a reduced error probability when maximum likelihood decoding is applied in the receiver.

Abstract: A circuit for maximizing power transfer from a station to an interactive memory card via a capacitive interface. A reader system in the station generates an ac signal which provides operating power that is transferred to the card through the capacitive interface formed when the card is placed against a window on the station. The ac signal from the station is directed through a series resonant circuit to the card. The capacitive interface between the station and card make up the capacitive element of the resonance circuit while the series combination of the secondary of a transformer and an electrically variable inductor form the inductive element. Use of the variable inductor allows the station to tune the circuit to resonance and cancel the capacitive element, thereby maintaining maximum power transfer to the card.