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This paper realized a serial communication using a pulse counting method. it introduced a call system in which each caller is coded by Quasi-digital and the host computer adopts the time-division process and the cyclic query to deal with signal sent by each caller in order to avoid the signal contention., finally it designed the circuit and implement the system. The wired call system is usually applied in the duty rooms in hospitals and the service counters in hotels to answer the help-seeking calls from the patients and guests respectively.

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