Panasonic Panafax UF-4000, Service Manual

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6.2.11 Receive Signal Control Circuit
This circuit consists of operational DAA and its peripheral circuit.
Up to this time, from Primary circuit to Secondary circuit such as Hybrid circuit, Analog circuit, Analog Front
End (AFE : A-D / D-A convertor) and Modem through Line transformer, and all the Received Signals to the
AFE are processed with Analog signals.
However at this time, the Received Signal is converted from Analog to Digital with DAA of Primary circuit,
and the Digital Signal is transferred to DAA (Si3022) of Secondary circuit as serial data. Therefore, unlike
other machine, this machine has No Analog Circuit of Secondary circuit, because of the DAA (Si3022) of
Secondary Circuit is able to transfer the Digital Signals directly to the Modem. Even at standby, this circuit is
connected with the Line via capacitor cutting Direct Current, this means it can be detected any Signals for
Ringer, CNG and DTMF remote commands.