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6.6.2. 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.
[IC1 → IC5 → IC5(3) → C48 → R37 → R38 → IC9 (2) → IC9 (1) → C53 → IC6 (2) → IC6 (1) → C58 → R49 → IC9 (6) → IC9
(7) → CN10 (1)] → CN202 (1) → C106 → R103 → R102 → T101 → C8 → Q4 (C) → Q4 (E) → D1 → TEL LINE
[ ]: Digital section
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).
TEL LINE → D1 → Q4 (E) → Q4 (C) → C8 → T101 → R104 → C107 → R112 → IC101 (6) → IC101 (7) → C127 → IC103
(11) → IC103 (10) → CN102 (10) → [CN9 (10) → IC6 (10) → IC6 (11) → R33 → C43 → IC5 (15) → IC5 → IC1]
[ ]: Digital section
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.
(DTMF Monitor Tone)
[IC1 → IC5 → IC5(3) → C48 → R37 → R38 → IC9 (2) → IC9 (1) → C54 → R44 → IC8 (2) → IC8 (1) → C27 → R13 → IC1
(62) → IC1 (63) →C62 → IC8 (5) → IC8 (7) → C67 → CN10 (9)] → CN202 (9) → R122 → IC102 (4) → IC102 (5) → SPEAKER
[ ]: Digital section
4. Call Tone Transmission
This is the call signal which is generated in the ASIC (IC1) and sent to the speaker.
[IC1 (59) → R28 → C45 → R35 → IC8 (2) → IC8 (1) → C27 → R13 → IC1 (62) → IC1 (63) → C62 → IC8 (5) → IC8 (7) →
C67 → CN10 (9)] → CN202 (9) → R122 → IC102 (4) → IC102 (5) → SPEAKER
[ ]: Digital section
5. Busy/Dial Tone Detection
The path is the same as FAX receiving.
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KX-FT21RS