Real Time Clocks-PCF8563T/F4,118

Real Time Clocks chip is one of the most widely used consumer electronics in daily life. It provides people with accurate real-time time, or for electronic systems to provide a precise time reference, Real Time Clocks chips mostly use a high-precision crystal oscillator as the clock source. Some clock chips in order to the main power supply the power down, but also can work, the need for additional battery power.

1). Early RTC products
Early RTC products are essentially frequency dividers with a computer communication port. It obtains time information such as year, month, day, hour, minute, and second by dividing and accumulating the oscillation frequency generated by the crystal and sending it to the processor for processing through the computer communication port.
The characteristics of RTC in this period are as follows: parallel port on the control port line; larger power consumption; using ordinary CMOS process; the package is double inline; the chip generally does not have the perpetual calendar and leap year and month automatic switching function that modern RTC has, and cannot handle the year 2000 problem. Now it has been eliminated.
2). Mid-term RTC products
In the mid-1990s, a new generation of RTC emerged, which uses a special CMOS process; power consumption is greatly reduced, with a typical value of about 0.5μA or less; power supply voltage is only 1.4V or less; and computer communication port has also become a serial mode, such as three-wire SIO / four-wire SPI, some products using a 2-wire I2C bus; packaging SOP / SSOP package, the volume The package adopts SOP/SSOP package, and the size is greatly reduced;
Functionality: the degree of on-chip intelligence has increased significantly, with perpetual calendar function, output control has also become flexible and diverse. Among them, Japan RICOH launched RTC has even appeared in the time base software tuning function (TTF) and oscillator stopping automatic detection function and the chip price is extremely low. At present, these chips have been used by customers in large numbers.
3). The latest generation of RTC products
The latest generation of RTC products, in addition to containing all the functions of the second generation of products, also added composite functions, such as low-voltage detection, main backup battery switching function, anti-printing board leakage function, and the package itself is smaller (height 0.85mm, area of only 2mm * 2mm).

Real Time Clocks chip time error is mainly from the clock chip in the crystal frequency error, and the crystal frequency error is mainly due to temperature changes caused. Therefore, the temperature of the crystal resonant frequency of the error generated by the effective compensation is the key to improving the accuracy of the clock. The quartz crystal resonant frequency error compensation method is based on the known error of the crystal resonant frequency with the change of temperature, to generate a 1Hz frequency division counter for an accurate compensation method.
The most important function of RTC is to provide the calendar function up to 2099, for time, no matter how fast or slow is the error, and the matching capacitor plays a very important role in the peripheral devices of RTC, it can properly correct the matching problem between the crystal and RTC.