Panasonic KX MC6020 Service Manual - Page 51
RTC Backup Circuit, Modem Circuit Operation
UPC - 037988840441
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KX-MC6020HX PIN NO. T9 T12 T13 T15 PinName GND_37 GND_38 GND_39 GND_40 I/O - Power SUPPLY VOLTAGE GND GND GND GND GND GND GND GND EXPLANATION 6.3.2. RTC Backup Circuit 1. Function This unit has a lithium battery (B300) which works for the Real Time Clock IC (RTC: inside IC300). The RTC continues to work, backed up by a lithium battery even when the power switch is OFF. 2. RTC Inside (IC300) Backup Circuit Operation When the power switch is turned ON, power is supplied to the RTC (inside IC300). At this time, the voltage at pin B22 of the IC300 is +3.3V. When the power switch is turned OFF, the B300 supplies power to RTC through D300. When the power switch is OFF and the voltage of +3.3V decreases, pin B22 of RTC (IC300) becomes roughly the same voltage as the battery voltage. RTC goes into the backup mode, in which the power consumption is lower. 6.3.3. Modem Circuit Operation The modem (Included IC300) has all the hardware satisfying the CCITT standards mentioned previously. ALL processing is controlled by the SOC (IC300) according to CCITT procedures. This modem (Included IC300) has an automatic application equalizer. With training signal 1 or 2 at the time of G3 reception, it can automatically establish the optimum equalizer. Facsimile Transmission/DTMF Line Send The digital image data sent on ATXD line from modem (Included IC300) . DAA IC100(6→9,10), Line side DAA IC101 and the NCU section to the telephone line. Facsimile Reception The analog image data which is received from the telephone line passes through the NCU section and enters line side DAA*1 IC100. The signals are changed to digital data in IC101 (5,6) ,IC100 (9,10→5) and IC300. In this case, the image signals from the telephone line are transmitted serially. 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. Busy/Dial Tone Detection The path is the same as Facsimile Reception. Call Tone Transmission This is the call signal which is generated the SOC (IC300) and sent to the speaker. *1 DAA : Direct Access Arrangement 51