What’s RTC 

RTC (stands for Real Time Clock) is a device that provides standard time for a system which runs in real time. RTCs are present in almost any electronic device which needs to keep accurate time. RTC could be an integrated circuit or embedded in a system. Many IC manufacturers make RTCs, including Epson, Intersil, Maxim, NXP Semiconductor, Texas Instruments and STMicroelectronics. The RTC was introduced to PC compatibles by the IBM PC/AT in 1984, which used a MC146818 RTC. Later Dallas Semiconductor made compatible RTCs, which was often used in older personal computers, and are easily found on motherboards because of their distinctive black battery cap and silkscreened logo. In newer systems the RTC is integrated into the south-bridge chip.

Although keeping time can be done without an RTC, using one has benefits:

• Low power consumption
• Frees the main system for time-critical tasks
• Sometimes more accurate than other methods

An example of RTC ICs is DS1337  (Dallas Semiconductor),  ISL12008 (Intersil), etc. An example of embedded RTC in microcontroller is 32-bit AVR UC3 D Series(Atmel) , C16X/ST10 (ARM), HMS81C7332, etc. Figure below is some typical operation circuit of an RTC (DS 1337) with microcontroller  

An RTC requires power back-up to keep time when primary power fails or off. It can be used rechargeable solid state batteries as a cost effective, small footprint, life-of-product replacement for traditional, bulkier power sources, such as coin cell batteries and super capacitors. If you need more information about power back up, you can click here.