Modem Circuit Operation - Panasonic KX-F900 Service Manual

KX-F900 I
5-2.MODEM CIRCUIT OPERATION
The modem (IC11) has all the hardware satisfying the IIU-I standards mentioned previously.
When the gate array IO1 (116) is brought to low level, the modem (IO11) is chip-selected and resistors inside IC are selected
by select signals from ASlO (IO1) A0-A4, commands are written through data bus, and all processing is controlled at the ASlC
(ICl) according to ITU-T procedures. Here the signal IN"-Tdispatched from _ (pin 52 of I011) to the ASlC (IO1) when
preparation for acceptance of transmission data is OK and when demodulation of reception data is complete, the ASIC (IO1)
implements post processing. This modem (IO11) has an automatic application equalizer. With training signal 1 or 2 at time of
G3 reception, it can automatically establish the optimum equalizer. Also, the modem (IO11) generates an internal clock of
24.00014MHz by means of an external crystal oscillator (Xl).
(1) Facsimile TransmissionlDTMF Line Send
The digital image data on the data bus is modulated in the modem (ICl 1), and sent from pin 44 via amplifier
IO10 (6 -,- 7), the NCU section to the telephone line.
C73- r R90 --* 1010(6-7) _ CNI(10) _ 0N271(10) _ C184 _ R182 -* IC151(73-63)
IC11 (44) -[_ C74-'
[C203 -" R210 ---*IC201(2-1) --* C202 -" R201 _ T101] -* TEL LINE.
[ ]: NCU section
(2) Facsimile Reception
The analog image deta Which is received from the telephone line passes through the NCU section and enters pin 45 of the
modem (IC11 ). The signals that enter pin 45 of the modem (IC11 ) 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 --* T101 -4 R202 --, C205 --* 10201(6-7) --* C210 --* C212 --* R215 --* C213 _ IO202(1-2) --* O217
CN271(9) --* Rll -* IC10(2-1) _ C19 ---* R13 -* IC11(45)
(3) DTMF Transmission (Monitor tone)
The DTMF signal generated in the modem (IC11) is output from pin 44, then passes through the analog G/A IO151, and
the NCU section to the telephone line as same as facsimile transmission signals.
(DTMF Monitor Tone)
IC11 (44) _ 073 _R90 -+ ICl 0(6-7) --, ON1 (10) _ 0N271 (10) --* C184 --* R184 --, I0151 (76-41) --* O158 --,R161 --,
074 -J
IC151 (40-38) --* R245 ---,0245 --, 10241 (4-5,8) _ Speaker
(4) Call Tone Transmission
The call signal which is generated in the ASIC (IC1) passes through analog G/A IC151 and IC241 (4 --, 8, 5) to the speaker.
I01(85,87) -_ R59 -* 056_* 0N2(1) --* 0N272(1) -+ R186 --* O187 _ IO151(78-41) --* C158 _ R161 ---*
R60 ---*C57 -J
IC151 (40-38) --, R245 --* C245 ---,IC241 (4-5,8) _ Speaker
(5) Busy/Dial 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
(IC11) becomes 1, and this status is monitored by the ASIC (IC1).
152