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*When an intercom transmission is not in use, the waveform of (D) becomes the same burst signal as (C). 2. Data Reception The data that is transmitted to the telephone line from another set is input via T701 in reverse order of the data transmission (D). This burst signal passes BPF701 to separate from the audio signal and then only 455 kHz is extracted (E) at pin 5 of IC701. This burst signal is amplified and demodulated at pin 4 of IC701 (I). The amplified burst signal (J) is input to pin 32 of the microcomputer IC801.