C8051F980-C-GM Datasheet, PDF (197/325 Pages) Silicon Laboratories – Ultra Low Power, 8-2 kB Flash, Capacitive Sensing MCU

C8051F99x-C8051F98x
20. SmaRTClock (Real Time Clock)
C8051F99x-C8051F98x 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 SmaRT-
Clock can operate directly from a 1.8–3.6 V battery voltage and remains operational even when the device
goes into its lowest power down mode. The SmaRTClock output can be buffered and routed to a GPIO pin
to provide an accurate, low frequency clock to other devices while the MCU is in its lowest power down
mode (see “PMU0MD: Power Management Unit Mode” on page 170 for more details). C8051F99x-
C8051F98x 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 “18. Reset Sources” on page 181 and Section
“15. Power Management” on page 162 for details on reset sources and low power mode wake-up sources,
respectively.
XTAL4
XTAL3 RTCOUT
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
RTC0KEY
RTC0ADR
RTC0DAT
Figure 20.1. SmaRTClock Block Diagram
Rev. 1.2
197