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U
KX-F1200
_-2. MODEM
CIRCUIT
OPERATION
] he modem (IC405) has all the hardware satisfying the CCII I sta_ldards mentioned previously.
When the gate array IC404 (73) is brought to low level, the modem (IC405) is chip-selected
and resistors inside IC are se-
lected by seleot signals from gate array (IC404) LAO-LA4, commands are written through data bus, and all processing is con-
trolled at the CPU (IC401) according to ITU-T procedures. Here the signal INT dispatched from IRQ (pin 52 of IC405) to the
CPU (IC401) and gate array IC404 is output when preparation for acceptance of transmission data is OK and when demodu-
lation of reception data is complete; the CPU (IC401) implements post processing.
This modem (IC405) has an automatic application equalizer. With training signal 1 or 2 at time of G3 reception, it can auto-
matically establish the optimum equalizer. Also, the modem (IC405) generates an internal clock of 24.00014 MHz by means
of an external crystal oscillator (Xl).
1) Facsimile Transmission
The digitalimage data on the data bus is modulated in the modem (IC405), and sentfrom pin 44 via amplifier IC413 (6--,7),
the NCU sectionto the telephoneline.
IC405(44) --* C508, C509 --, R502, R503 --* IC413(6 --* 7) --, CN401(1) _ C146 --, R192 _ IC7(3 --, 2) -* NCU Section
[R30 _ C29 --* IC14 (6 --* 7) -* R20 -* T1] -* Line1
._Line2 is the same. (IC7 ---*IC15 --* T2 --* Line2)
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 (IC5). The signals that enter pin 45 of the modem (IC5) 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, internal the equalizer circuit reduces the image signals to the long-distance
receiving level.
It is designed to correct the characteristics
of the frequency band centered about 3 KHz and maintain a constant receiving
sensitivity.
It can be set in the service mode.
TEL. Line _ NCU Section -* CN401(2) --, C521 _ R509, R508 --, IC413(2 --* 1) -* C519 -* R507 --* IC405(45)
3) DTMF Transmission
(Line send)
When dialing with handset or speaker-phone, DTMF signal is output from DTMF generator [IC4 (Analog Board)]. When dial-
ing with FAX, DTMF signal is output from Modem [IC405 (Digital Board)].
4) BusylDial Tone Detection
The path is the same as for FAX receiving. When it is detected, the carrier detect bit of the resistor in the modem (IC405) be-
comes 1, and this status is monitored by CPU (IC401). (Auto FAX dialing only)
When dialing with handset or speaker-phone,
it is detected by IC13 (Analog Board) and it is output to I/O port [IC1 (Analog
Board).
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