C8051F980-C-GM Datasheet, PDF (5/325 Pages) Silicon Laboratories – Ultra Low Power, 8-2 kB Flash, Capacitive Sensing MCU

C8051F99x-C8051F98x
19.2.Low Power Internal Oscillator......................................................................... 189
19.3.External Oscillator Drive Circuit...................................................................... 189
19.3.1.External Crystal Mode............................................................................ 189
19.3.2.External RC Mode.................................................................................. 191
19.3.3.External Capacitor Mode........................................................................ 192
19.3.4.External CMOS Clock Mode .................................................................. 192
19.4.Special Function Registers for Selecting and Configuring the System Clock 193
20. SmaRTClock (Real Time Clock) .......................................................................... 197
20.1.SmaRTClock Interface ................................................................................... 198
20.1.1.SmaRTClock Lock and Key Functions................................................... 198
20.1.2.Using RTC0ADR and RTC0DAT to Access SmaRTClock Internal Registers
..................................................................................................... 199
20.1.3.RTC0ADR Short Strobe Feature............................................................ 199
20.1.4.SmaRTClock Interface Autoread Feature .............................................. 199
20.1.5.RTC0ADR Autoincrement Feature......................................................... 200
20.2.SmaRTClock Clocking Sources ..................................................................... 203
20.2.1.Using the SmaRTClock Oscillator with a Crystal or External CMOS Clock
..................................................................................................... 203
20.2.2.Using the SmaRTClock Oscillator in Self-Oscillate Mode...................... 204
20.2.3.Using the Low Frequency Oscillator (LFO) ............................................ 204
20.2.4.Programmable Load Capacitance.......................................................... 205
20.2.5.Automatic Gain Control (Crystal Mode Only) and SmaRTClock Bias Dou-
bling ..................................................................................................... 206
20.2.6.Missing SmaRTClock Detector .............................................................. 208
20.2.7.SmaRTClock Oscillator Crystal Valid Detector ...................................... 208
20.3.SmaRTClock Timer and Alarm Function ........................................................ 208
20.3.1.Setting and Reading the SmaRTClock Timer Value .............................. 208
20.3.2.Setting a SmaRTClock Alarm ................................................................ 209
20.3.3.Software Considerations for using the SmaRTClock Timer and Alarm . 210
21. Port Input/Output.................................................................................................. 215
21.1.Port I/O Modes of Operation........................................................................... 216
21.1.1.Port Pins Configured for Analog I/O....................................................... 216
21.1.2.Port Pins Configured For Digital I/O....................................................... 216
21.1.3.Interfacing Port I/O to 5 V Logic ............................................................. 217
21.1.4.Increasing Port I/O Drive Strength ......................................................... 217
21.2.Assigning Port I/O Pins to Analog and Digital Functions................................ 217
21.2.1.Assigning Port I/O Pins to Analog Functions ......................................... 217
21.2.2.Assigning Port I/O Pins to Digital Functions........................................... 218
21.2.3.Assigning Port I/O Pins to External Digital Event Capture Functions .... 218
21.3.Priority Crossbar Decoder .............................................................................. 219
21.4.Port Match ...................................................................................................... 225
21.5.Special Function Registers for Accessing and Configuring Port I/O .............. 227
22. SMBus ................................................................................................................... 235
22.1.Supporting Documents ................................................................................... 236
22.2.SMBus Configuration...................................................................................... 236
Rev. 1.2
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