Panasonic KX-FP101AL Service Manual page 157

6.6.2. MODEM CIRCUIT OPERATION
The 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 selected
by the select signals from ASIC (IC501) ADR0-ADR4(pin 107~111). Commands are written through the data bus, and all
processing is controlled by the ASIC (IC501) according to CCITT procedures. Here, the INT signal dispatched from IRQ (pin 52 of
IC505) to the ASIC (IC501) implements post processing.
This modem (IC505) has an automatic application equalizer. With training signal 1 or 2 at the time of G3 reception, it can
automatically establish the optimum equalizer. The modem (IC505) clock is supplied by pin 70 of ASIC (IC501).
1. Facsimile Transmission/DTMF Line Send
The digital image data on the data bus is modulated in the modem (IC505), and sent from pin 44 via amplifier IC511 (24→25),
and the NCU section to the telephone line.
Refer to 2.3.3.5. Analog Board Section.
2. Facsimile Reception
The analog image data which is received from the telephone line passes through the NCU section and enters pin 45 of the
modem (IC505). The signals that enter pin 45 of the modem (IC505) are demodulated in the board to digital image signals, then
placed 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 around 3 kHz and maintain a constant receiving
sensitivity.
It can be set in the service mode.
Refer to 2.3.3.5. Analog Board Section.
3. DTMF Transmission (Monitor tone)
The DTMF signal generated in the modem (IC505) is output from pin 44, and the NCU section to the telephone line the same
as facsimile transmission signals.
(DTMF Monitor Tone)
Refer to 2.3.3.5. Analog Board Section.
4. Call Tone Transmission
This call signal is generated in the ASIC (IC501) and sent to the speaker.
5. Busy/Dial Tone Detection
The path is the same as FAX receiving. When it is detected, the carrier detect bit of the resistor in the modem (IC505) becomes
1, and this status is monitored by ASIC (IC501).
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