Panasonic KX-FLM652CX Service Manual page 168

KX-FLM652CX
7.3.3. MODEM CIRCUIT OPERATION
The modem (IC607) has all the hardware satisfying the CCITT standards mentioned previously.
When the ASIC IC600 is brought to a low level, the modem (IC607) is chip-selected and the resistors inside IC are selected by the
select signals from ASIC (IC600) A[0]-A[5]. Commands are written through the data bus, and all processing is controlled by the
ASIC (IC600) according to CCITT procedures. Here, the INT signal dispatched from IRQ (pin 1 of IC607) to the ASIC (IC600)
implements post processing.
This modem (IC607) 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 (IC607) operates using the 28.224MHz clock (X604).
1. Facsimile Transmission/DTMF Line Send
The digital image data on the data bus is modulated in the modem (IC607), and sent from pin 25, 26 via modem IC607, Analog
gate array IC209(24→22), amplifier IC204(6→7) and the NCU section to the telephone line.
Refer to CHECK SHEET(P.136).
2. Facsimile Reception
The analog image data which is received from the telephone line passes through the NCU section and enters pin 29 of the
modem (IC607). The signals that enter pin 29 of the modem (IC607) 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 CHECK SHEET(P.136).
3. DTMF Transmission (Monitor tone)
The DTMF signal generated in the modem (IC607) is output from pin 25, 26 and the NCU section to the telephone line the same
as facsimile transmission signals.
(DTMF Monitor Tone)
Refer to CHECK SHEET(P.136).
4. 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 (IC607) becomes
1, and this status is monitored by ASIC (IC600).
5. Call Tone Transmission
This is the call signal which is generated the ASIC (IC604) and sent to the speaker.
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