C8051F970-A-GM Datasheet, PDF (253/454 Pages) Silicon Laboratories – Low Power Capacitive Sensing MCU with up to 32 kB of Flash

C8051F97x
25. SmaRTClock (Real Time Clock, RTC0)
C8051F97x devices include an ultra low power 32-bit SmaRTClock Peripheral (Real Time Clock) with alarm. The
SmaRTClock has a dedicated 32 kHz oscillator that can be configured for use with or without a crystal. No external
resistor or loading capacitors are required. The on-chip loading capacitors are programmable to 16 discrete levels
allowing compatibility with a wide range of crystals. The SmaRTClock can operate directly from a 0.9–3.6 V battery
voltage and remains operational even when the device goes into its lowest power down mode. C8051F97x devices
also support an ultra low power internal LFO that reduces sleep mode current.
The SmaRTClock allows a maximum of 36 hour 32-bit independent time-keeping when used with a 32.768 kHz
Watch Crystal. The SmaRTClock provides an Alarm and Missing SmaRTClock events, which could be used as
reset or wakeup sources. See Section “27. Reset Sources and Supply Monitor” on page 323 and Section
“16. Power Management” on page 94 for details on reset sources and low-power mode wake-up sources,
respectively.
XTAL4
XTAL3
SmaRTClock
Programmable Load Capacitors
SmaRTClock Oscillator
LFO
32-Bit
SmaRTClock
Timer
Power/
Clock
Mgmt
SmaRTClock State Machine
Wake-Up
Interrupt
Internal
Registers
CAPTUREn
RTC0CN
RTC0XCN
RTC0XCF
ALARMn
Interface
Registers
RTC0ADR
RTC0DAT
Figure 25.1. SmaRTClock Block Diagram
254
Rev 1.0