Abstract: A data transmission system uses a malfunction detection circuit for detecting malfunction conditions between a data transmitting station and a data receiving station connected with first and second data transmission lines. The malfunction circuit senses a data signal of a first polarity for a preselected duration and provides an output signal when the data signal exceeds the preselected duration. The circuit also supplies a detection signal of a second preselected duration in a polarity opposite the data signal and detects the presence of or the absence of the detection signal. The circuit thereafter provides an output signal indicative of the malfunction condition when the absence of the detection signal exceeds the second preselected duration.

Abstract: An automatic meter reader includes a microprocessor connected through digital logic circuitry and a telephone interface to a metering transducer and a telephone line, to develop modulated signals for reporting of registered meter data and for sampling of received signals to detect a carrier and to effect demodulation and develop control data. A count-down arrangement is used for developing the modulated signals. In sampling received signals, a sample count is developed which is proportional to the duration of one cycle of a received signal and which is compared with stored counts for detection of a carrier and for demodulation. A debounce arrangement is included in the logic circuitry.