Rtc (Real Time Clock) Circuit - Panasonic JS-170FR Series Service Manual

2.1.2.2

RTC (Real Time Clock) circuit

The FW82371EB incorporates an RTC function.
The RTC includes the hardware for clock and calendar functions and the battery backup type CMOS-RAM that can manage the
hardware setup information.
Operation is compatible with the MC146818.
To actuate the RTC, it is necessary to install the battery and the oscillator externally.
The oscillatory frequency is 32.768kHz, fixed. The clock is also of the backup type.
This system uses a lithium battery to back up the RTC circuit.
The battery (BT_1) is a charge-disabled coin type primary battery that maintain a voltage of about +3.0V.
When the power supply is ON, +3V (+3.3V) is turned to the RTCVCC voltage via D_1. When the power supply is OFF, the
battery voltage is used as the RTCVCC voltage via D_2.
The C_1 capacitor is a backup capacitor to be used during the replacement of battery.
The battery backup time is only about 2 minutes, and therefore care must be taken at the time of replacement.
10M
X2
32. 768KHz
22p
D_1
+3V
M A 704
R_1
1K
D_2
M A704
BT_1
C R 2450
FW82371EB
RTCVCC
L16
VCC(RTC)
N19
RTCX1
R20
RTCX2
RTC
22p
RTCVCC
0. 1u
2-9
TP1
R_2
100
+
C_1
680uF