LG KG270 Service Manual - Page 24

3. TECHNICAL BRIEF 3.4 RTC(32.768KHz Crystal) 32.768KHZ CRYSTAL 32KIN 32KOUT X100 4 3 1 2 MC-146_12_5PF 32.768KHz C104 18p C105 18p Figure. 3-4 E-Gold Voice RTC Interface The integrated Real Time Clock (RTC) is able to provide programmable alarm functions and external interrupts. Due to its extreme low power consumption the RTC can be supplied from a small backup battery. This allows the generation of external interrupts, even when the main PMB7880 supply voltage is switched off. For this purpose the RTC is powered by own voltage supply pins VDD_RTC and VSS_RTC. The RTC shall be driven by a 32.768 kHz (32k) clock which needs to be applied via the PMB7880 F32K and OSC32K pins. The clock can be fed from either an external clock source or use the on chip 32 KHz oscillator module. The low clock frequency and the optimized low power design give the possibility to run the chip with a minimum of power dissipation. For example, for this specific application the 26 MHz reference oscillator can be switched off during system standby and a lowpower time reference can be kept when the 32k clock is provided to the RTC. The RTC consists of an PMB7880 specific RTC shell, containing the RTC macro, as well as the 32 kHz oscillator, as described in the following sections. The module RTC Shell solely performs level translation of the 32KHz clock to the VDD_LD1 power supply domain, and is not functionally associated with the RTC. - 25 -