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5.6.2. MODEM CIRCUIT OPERATION
The ASIC (IC1) has all the hardware satisfying the ITU-T standards mentioned previously. / The
modem is included in IC1. The signal communicates with the TEL line through the analog front
end IC (IC5) of digital/analog, analog/digital convertor. The modem in IC1 is operated using the
20.736 MHz (x2) clock.
1. Facsimile Transmission/DTMF Line Send
The digital image data on the data bus is modulated in the modem
(IC1), and sent to analog front end (IC5) as the digital data, then it
is converted to the analog signal there. Passing through IC9 and
IC6, the signal is sent to NCU section.
Refer to
CHECK SHEET
2. Facsimile Reception
The analog image data which is received from the telephone line
passes through the NCU section and enters pin 15 of the analog
front end (IC5). The signals that enter pin 15 of the analog front
end (IC5) convert the analog signals to the digital signals, then the
data is sent to the modem (IC1).
Refer to
CHECK SHEET
3. DTMF Transmission
The DTMF signal generated in the ASIC (IC1) is sent to the analog
front end (IC5) to perform the digital/analog conversion, then
output from pin 3 of IC5, and is then sent to the circuit on the
same route as used for facsimile transmission.
Refer to
CHECK SHEET
4. Call Tone Transmission
This is the call signal which is generated in the ASIC (IC1) and
sent to the speaker.
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