RTC

Real-Time Clock (RTC) is a clock-based hardware component used in computers and embedded devices to keep track of the current time and date. It typically runs on a low-power oscillator, such as a 32.768 kHz quartz crystal, and is designed to continue running on battery power when main system power is removed.

An RTC maintains calendar and time information including seconds, minutes, hours, day, month, and year, often including leap year handling. Many devices also provide alarm and timer functions and a configurable square-wave output for other components or peripherals. RTCs with temperature compensation improve accuracy over varying temperatures.

Interfaces: RTCs can be standalone chips connected via interfaces such as I2C, SPI, or 1-Wire, or they can be integrated into a microcontroller as an internal peripheral. In desktop and laptop systems, an RTC often accompanies CMOS memory and is powered by a dedicated coin-cell battery. During boot, the operating system reads the RTC to establish the current time; after boot, network time protocols (NTP) may be used to synchronize time and correct drift.

Considerations: Accuracy depends on crystal stability and temperature; some RTCs include calibration features or use temperature-compensated crystals. Battery health affects the ability to retain time during power loss. In practice, RTCs provide a persistent time reference for system software and timing-sensitive applications, while higher-level timekeeping can be synchronized over a network.