RTC FULL FDORM| does RTC mean?


Definition:Real Time Clock
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What does RTC mean?

Real-Time-Clock (RTC) is a computer clock, usually in the form of an Integrated Circuit (IC) that keeps track of the current time. As the name suggests, the RTC keeps track of time in real mode.

RTC is incorporated into computer motherboards and embedded systems requiring access to the time. RTC is usually run on a special internal battery to retain the time. As a result, even if the power of the system is turned off, the RTC clock keeps running.

Real-Time Clock (RTC)

What Does Real-Time Clock (RTC) Mean?

A real-time clock (RTC) is a computer clock, usually in the form of an integrated circuit that is solely built for keeping time. Naturally, it counts hours, minutes, seconds, months, days and even years.

RTCs can be found running in personal computers, embedded systems and servers, and are present in any electronic device that may require accurate time keeping.

Being able to still function even when the computer is powered down through a battery or independently from the system’s main power is

Techopedia Explains Real-Time Clock (RTC)

RTCs must accurately keep time, even when the device is powered off because, it is often used as a trigger for turning the device on or triggering events such as alarm clocks. RTC ICs run on an alternate power source, which allows it to continually operate under low power or even when the computer is turned off.

ICs on older systems utilize lithium batteries, whereas newer systems make use of auxiliary batteries or supercapacitors. RTC ICs that use supercapacitors are rechargeable and can be soldered. But in most consumer-grade motherboards, the RTC is powered by a single battery that, when removed, resets the RTC to its starting point.

TC ICs regulate time

RTC ICs regulate time with the use of a crystal oscillator and do not rely on clock signals like most hardware clocks. Aside from being responsible for the timing function of the system and its clock, RTC ICs ensure that all processes occurring in the system are appropriately synchronized.

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Although some may argue that this is a job for the system clock, the system clock is actually dependent on the RTC, making the RTC indirectly responsible for synchronization.

An RTC battery should last for three to five years or more. RTCs are essential; if the battery fails, it must be replaced to ensure continued operation.

A dead battery can be diagnosed with an error message at startup or if the user finds that the clock or the setup configuration has become corrupted, flaky or odd.

Benefits of RTCs include:

  • RTC ICs have proved to be more precise than other methods — like programming the timer of the controller.
  • It frees the main system from time-critical tasks.
  • It has low power consumption and improved frequency stability.

Real-Time Clocks

A real-time clock (RTC) is an IC that keeps an updated track of the current time.

This information can be read by a microprocessor, usually over a serial interface to facilitate the software performing functions that are time dependent. RTCs are designed for ultra-low power consumption as they usually continue running when the main system is powered down.

This enables them to maintain current time against an absolute time reference, usually set by the microprocessor directly. Figure 1 depicts the typical internal workings of a simple RTC.

Figure 1: The Internal Circuit Blocks of a PCA21125

RTCs are a very common element. They are present in everything from the instrument clusters and infotainment systems in automotive applications to house metering. RTCs frequently integrate into other devices—for example, the broadband communications ICs used in car radios.

They usually interface to a microprocessor circuit by an SPI or I2C serial bus, and may contain a number of other functions like backup memory, a watchdog timer for supervising the microprocessor and countdown timers to generate real time event. Some RTCs include second or minute interrupt outputs and are even clever enough to account for leap years (see figure 2).

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Figure 2: Data flow diagram of a time function.

An RTC maintains its clock by counting the cycles of an oscillator

An RTC maintains its clock by counting the cycles of an oscillator – usually an external 32.768kHz crystal oscillator circuit, an internal capacitor based oscillator, or even an embedded quartz crystal. Some can detect transitions and count the periodicity of an input that may be connected.

This can enable an RTC to sense the 50/60Hz ripple on a mains power supply, or detect and accumulate transitions coming from a GPS unit epoch tick. An RTC that does this operates like a phase locked loop (PLL), shifting its internal clock reference to ‘lock’ it onto the external signal. If the RTC loses its external reference, it can detect this event (as its PLL goes out of lock) and free run from its internal oscillator.

Some RTCs maintain the oscillator setting at the last known point before it went out of lock with the input. Time resolution is an important consideration – how accurately do you need to read the current time? This is specified by the RTC datasheet, but is ultimately limited by the oscillator frequency.

An RTC that is running from its own internal reference will integrate

An RTC that is running from its own internal reference will integrate an error related to the absolute accuracy of the crystal reference, and is effected by a number of conditions including temperature. Crystals are specified to operate within a temperature range, usually around -10°C ~ 60°C – and their accuracy is reduced if a design deviates outside this (figure 3).

Some RTCs have integrated temperature compensation that can extend and increase the accuracy of the crystal oscillator circuit. Crystals also age, and this changes their physical nature, which leads to additional errors.

Typical low cost crystals have frequency tolerance of around +/-20ppm (parts per million), and slowly accumulate errors. A +/-20ppm crystal could drift as far as 72mS every hour, or 1.7 seconds per day. They occasionally require recalibration to correct for the drift.

The connected processor obtains an updated ‘system time’ in some way and writes this new value to the RTC for it to start counting from. This system time could come from manual input from a user interface, reading a GPS unit or from a cloud connection.deviation of frequency with temperature


Figure 3: The deviation of frequency with temperature of a typical 32.768kHz crystal.

RTCs need continuous power and must have extremely low power consumption. Most RTCs use the digital circuits supply when the device is on and active, but switch over to a continuously connected power source when the circuit is powered down. This power source could be a dedicated battery, a charged supercapacitor or a separate power supply from mains.

Many RTCs can detect this change-over and go into an ultra-low power state where they power down all circuitry except those essential for maintaining the clock in order to conserve battery life. RTCs can also include alarm functions – set times that when reached trigger the RTC to drive an output that wakes the processor up.

Real Time Clocks (RTC) IC

Renesas real-time clocks (RTC IC) are ultra-low-power clock/date devices with programmable time-of-day alarms and programmable square-wave outputs. These devices offer high noise immunity, low current consumption, 12/24 hour mode of operation, auto correction for leap year, and programmable square wave output, making them ideal for a wide range of design applications.

Renesas’ real-time clock ICs count seconds, minutes, hours, day, date, month, and year with leap-year compensation valid up to 2100. The devices feature normal and fast-mode I2C interfaces, two time-of-day alarms, an oscillator stop flag, programmable square-wave outputs that default to 32kHz on power-up, and operating voltages ranging from 1.8V to 5.5V. The IDT 1338 real-time clock IC includes a 56-Byte battery-backed non volatile RAM for data storage.

About Real-Time Clocks (RTC IC)

A real-time clock IC (RTC IC) is an integrated circuit that keeps track of the current time and date, typically counting seconds, minutes, hours, day, month, and year with leap-year compensation. Although the term often refers to the devices in personal computers, servers and embedded systems, real-time clock ICs are present in almost any electronic device which needs to keep accurate time.

Most of Renesas’ real-time clocks use an external crystal oscillator, but some contain an integrated oscillator to simplify the circuit and reduce the bill-of-materials (BOM). Most often, the oscillator’s frequency is 32.768kHz, or, exactly 2^15 cycles per second; making it a convenient rate to use with binary counter circuits.

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