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Real Time Clock (RTC)
The PCH contains a real-time clock functionally compatible with the Motorola* MC146818B. The real-time clock has 256 bytes of battery-backed RAM. The real-time clock performs two key functions—keeping track of the time of day and storing system data even when the system is powered down as long as the RTC power well is powered. The RTC operates on a 32.768 kHz oscillating source and a 3 V battery or system battery if configured by design as the source.
The RTC also supports two lockable memory ranges. By setting bits in the configuration space, two 8 byte ranges can be locked to read and write accesses. This prevents unauthorized reading of passwords or other system security information.
The RTC also supports a date alarm that allows for scheduling a wake up event up to month in advance.
| Acronyms | Description |
|---|---|
| BCD | Binary Coded Decimal |
| CMOS | Complementary Metal Oxide Semiconductor. A manufacturing process used to produce electronics circuits, but in reference to RTC is used interchangeably as the RTC’s RAM i.e. clearing CMOS meaning to clear RTC RAM. |
| ESR | Equivalent Series Resistance. Resistive element in a circuit such as a clock crystal. |
| GPI | General Purpose Input |
| PPM | Parts Per Million. Used to provide crystal accuracy or as a frequency variation indicator. |
| RAM | Random Access Memory |