Advertisement
system setup date and so on are stored in the RAM (IC3). / The
RTC continues functioning, even when the power switch is OFF,
backed up by a lithium battery.
2. Circuit Operation
When the power is turned ON, power is supplied RAM (IC3) and
RTC (IC1). / At this time, the voltage at pin 28 of RAM is +5V and
pin 3 of RTC (IC1) is +3.3V. When the power is turned OFF, the
battery supplies the power to RAM and RTC through J1, R14,D1 or
D7. At that time, the voltage at pin 28 of RAM and pin 3 of IC1 are
about +2.5V. When the power is OFF and the +5V and +3.3V
voltages decrease, IC4 detects them and LOW is input to pin 17 of
IC1. Pin 16 of IC1 outputs the reset signals. Pin 28 of RAM (IC3)
and pin 3 of RTC (IC1) become low, then RAM and RTC (IC1) go
into the back up mode, when the power consumption is lower.
129
Advertisement
