Rtc Backup Circuit; Modem Circuit Operation - Panasonic UF-5500 Service Manual

UF-5500 / 4500
6.3.2.

RTC Backup Circuit

1. Function
This unit has a lithium battery (BAT300) which works in 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 AF3 of the
IC300 is +3.3V. When the power switch is turned OFF, the BAT300 supplies power to RTC through DA300.
When the power switch is OFF and the voltage of +3.3V decreases, pin AF3 of RTC (IC300) becomes roughly the same volt-
age 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*
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.
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* DAA : Direct Access Arrangement
Circuit Diagram
+3.3V/BATT
R388
IC303
1
2
C322
+3.3V
IC300
AD4 NBATRST
C319
AD5 VDD2RTC
3
C327
4
AF3 VDDIO33OSC
AF4 RTCCLKIN
AE4 RTCCLKOUT
X303
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