Integrated circuits (ICs) are essential elements that have revolutionized modern electronics. Microprocessors, microcontrollers, and now microchips are the newest IC types.

Microchips are small electrical devices with many related parts that are imprinted on a single semiconductor material. One of the peripherals inside the microcontroller that is most frequently used is the real-time clock (RTC).

What is a real-time clock?

A real-time clock is a crucial electronic circuit in many systems that accurately displays the current time in a human-readable format. It is a battery-operated digital clock that guarantees continuous operation even in the event of a power outage.

They come in a variety of packaging options. They are either externally connected to the microcontroller via communication interfaces or embedded in the microprocessor. The RTC saves the electronic system’s description or values in memory.

When the electronic system is turned on, the read-only memory (ROM) retrieves the current time from the RTC's memory. An RTC can track extended timelines even when a microcontroller is rebuilt or disconnected from a power source or USB.

Construction and Working of Real-Time Clock

The design options available for RTC are numerous. Every RTC has distinct features that can be applied to various applications as per its requirements. The most important part of RTC is the block unit.

As shown in Fig. 1, the basic building components required for any RTC are an oscillation circuit, frequency divider, bus interface, register, counter, and power management.

Fig. 1: RTC Block Diagram from SII-IC Semiconductor. Source: EPJ Web of Conferences

Oscillator

The most essential part of an RTC's operation is an oscillator, which is a dependable clock source. Using a quartz crystal oscillating at 32.768 kHz, a precise clock source for RTC is produced. This specific quartz crystal was selected because of its stability and ease of reduction to a frequency of 1 Hz using a divider circuit.

Furthermore, we cannot detect the vibration of this particular crystal frequency because it is beyond the audible range. Because the RTC can accurately track the date and time as it maintains registers for seconds, minutes, hours, days, months, and years,

Frequency Divider

RTC requires a precise, low-frequency clock signal to function. On the other hand, the main crystal oscillator runs at 32.768 kHz, which is a comparatively higher frequency. A frequency divider is used to reduce higher frequencies to a lower frequency.

A frequency divider circuit can be used to split the 32.768 kHz signal by 32,768 to produce a 1 Hz signal. Typically, a sequence of counters that divide the frequency by a power of 2¹⁵ is used.

The primary component influencing RTC precision is this divided clock signal. Battery-operated devices can operate with less power consumption because of the frequency divider's lower-frequency signals, which also increase the devices' lifespan.

Register

The frequency divider produces a 1 Hz output, which is received by the clock and calendar registers, also known as the time-keeping registers. The time, date, month, and year data are stored and maintained via these registers, which update continually every second. It is possible to simultaneously designate a separate counter for seconds, minutes, hours, days, weeks, months, and years.

The seconds register is getting updated every second. As the seconds register reaches from 0 to 60, it will reset to 0, and immediately, the minutes register will advance by one. The minute register is updated every 60 seconds. The minute register will continue from 0 to 60 counts and then reset to 0. The hours register will then increase from 0 to 24 and reset to zero.

After the entire day, the date register will begin to increase. This increment flow will continue just as it occurs in real-time until it reaches a year. After that, it will continue for the following year. Each month has a unique number of days, and the number of days in February determines the leap years. These registers carefully track this change in date based on the month and year.

In addition to the above-mentioned timekeeping registers, additional control and alarm registers are used to configure the RTC, handle alarms, and transmit signals at specific moments. Temperature compensation sensors are a feature of advanced RTC devices that enable them to operate in a broad temperature range.

Communication Interface

The most frequently used communication interfaces for RTC are the SPI interface and the I2C bus interface. Each interface provides advantages of its own, depending on the application.

They enable communication and data exchange between a microprocessor or microcontroller and a number of additional RTC components. They can access and configure the date and time information stored in the RTC registers.

Power Control Circuit

RTCs are low-power devices that consume minimal power in the range of nanoamperes. Every component of the circuit receives power from an external source, and in the event of a power outage, a battery powers them to keep recording time accurately and without interruption.

Applications

RTCs are long-lasting, cost-effective, and low-power devices that can be used for a variety of applications. It is more commonly used in servers, PCs, smartphones, fitness trackers, digital cameras, etc., to save the system time and date even when the device is turned off.

Furthermore, it is used by a large number of embedded systems and Internet of Things applications, including smart meters, thermostats, and security cameras. It is also essential for industrial automation systems and medical devices where accurate timekeeping is needed.

In conclusion, RTCs are critical for a variety of applications demanding exact timekeeping since they preserve system time and date even when devices are turned off.

Summarizing the Key Points

● Real-time clocks are crucial for accurate timekeeping in electronic devices, utilizing quartz crystals for stability and frequency division to generate precise clock signals.

● RTCs consist of essential components like oscillators, frequency dividers, registers, and communication interfaces for seamless operation.

● Lower-frequency signals in RTCs reduce power consumption, extending battery life in devices like digital cameras, smartphones, and IoT applications.