REAL TIME CLOCK

REAL TIME CLOCK

When you want to check or reset your computer date, you typically right click on the time value being displayed in the Windows tool bar (right bottom corner of your screen), right click and adjust the time. Well, you have just accessed the real time clock (RTC) of your system. There are two types of clocks in a computer: the CPU clock and the real time clock. The CPU clock governs the time used to run processes (like opening files and computing commands) while the RTC takes care of the time as referred to GMT.

Real time clocks run on a special battery and are not turned off even when your computer is switched off. Real time cocks measure time as the situation is happening and reacts to instructions as they are given.

How real time clocks work:

The main components of an RTC are an oscillator circuit and a crystal. The nominal oscillating frequency of the crystal is usually set at 32,768 Hz and this frequency is used to calibrate and derive the time using the circuit.

RTCs have a temperature compensation feature (of 25° Centigrade) that ensure accuracy with reasonable rise or fall in temperatures. In addition, the crystal has a load capacitance (CL) to overcome the parasitic capacitance of the surrounding PCB connections. There are two types of clocks: ISA and PC.

RTC starts functioning the instant the system is booted and before the OS begins loading. It overrides the system BIOS and writes the time in the CPU clock, each time any time changes are done to the BIOS. This ensures that both clocks are synchronized.

Where RTCs are used:

All computers have an RTC. Mission critical applications like space missions, advanced shipping navigation controls, and large ERP networks run on a real-time basis where every transaction occurs every second. Nowadays, even gaming sites that allow multiple users to play network games (e.g. Unreal Tournament, Half-Life) operate in a real time environment.