Panasonic KX-FP85 Service Manual

Also see for KX-FP85: Operating instructions Service manual

Contents

6.6.2. MODEM CIRCUIT OPERATIONThe modem (IC505) has all the hardware satisfying the CCITT standards mentioned previously.When the ASIC IC501 (77) is brought to a low level, the modem (IC505) is chip-selected and the resistors inside IC are selectedby the select signals from ASIC (IC501) ADR0-ADR4. The commands are written through the data bus, and all the processing iscontrolled by the ASIC (IC501) according to CCITT procedures. The INT signal dispatched from IRQ1, 2 (pins 108 and 121 ofIC505) to ASIC (IC501) when the transmission data is accepted and the received data is demodulated, the ASIC (IC501)implements post processing. This modem (IC505) has an automatic application equalizer.With training signal 1 or 2 during G3 reception, it can automatically establish the optimum equalizer. The modem (IC505) operatesusing the 32.256 MHz clock (X503).1. Facsimile TransmissionThe digital image data on the data bus is modulated in the modem (IC505), and sent from pin 69 via amplifier IC101 and theNCU section to the telephone line.Refer to 2.3.7.1 CHECK SHEET(P.76).2. Facsimile ReceptionThe analog image data which is received from the telephone line passes through the NCU section and enters pin 60 of themodem (IC505). The signals that enter pin 60 of the modem (IC505) are demodulated in the board to digital image signals, thenplaced on the data bus.In this case, the image signals from the telephone line are transmitted serially. Hence, they are placed on the bus in 8 bit units.Here, the internal equalizer circuit reduces the image signals to a long-distance receiving level.This is designed to correct the characteristics of the frequency band centered about 3 kHz and maintain a constant receivingsensitivity. It can be set in the service mode.Refer to 2.3.7.1 CHECK SHEET(P.76).3. DTMF Transmission (Monitor tone)The DTMF signal generated in the modem (IC505) is output from pin 69, and is then sent to the circuit on the same route asused for facsimile transmission.Refer to 2.3.7.1 CHECK SHEET(P.76).(DTMF Monitor Tone)Refer to 2.3.7.1 CHECK SHEET(P.76).4. Call Tone TransmissionThis is the call signal which is generated in the ASIC (IC501) and sent to the speaker.Refer to 2.3.7.1 CHECK SHEET(P.76).5. Busy/Dial Tone DetectionThe path is the same as FAX receiving. When it is detected, the carrier detect bit of the resistor in the modem (IC505) becomes1, and this status is monitored by the ASIC (IC501).165KX-FP85