Change manner and this change manner of the operational mode in the modem the modem null of

摘要

"MODEM WITH LOW PART COUNTAND IMPROVED DEMODULATOR"Abstract of the DisclosureAn FSK modem for coupling a standard dataport (50) to a telephone line (45) in which thesignal path between the phone line and the dataport passes through a processor (55). The samefrequency detection apparatus (83, 192, 180) isused to both demodulate FSK encoded signals anddetect the presence of a telephone ringing signalon the line. A pair of impedances (161, 162)provide alternate paths either through an inputfiltering network (167) or bypassing the network(135, 69) in a manner which allows the ring signalsto pass directly to the input (69) of the frequencydetector while assuring that only filtered FSKsignals reach the input. Also shown is the use ofthe same frequency synthesizing apparatus (86, 253,259) for generating FSK output signals and highgroup DTMF signals with appropriate switchableattenuation (88) provided in this signal path.