The running of each program requires a constant amount of frequency, so we will need to use the clock chip to generate the clock frequency. The clock chip is one of the most widely used consumer electronics products in daily life. It provides people with accurate real-time time, can count the year, month, day, Sunday, hour, minute, second, and has a variety of functions such as leap year compensation; or provide an accurate time reference for the electronic system, the current real-time clock Most of the chips use a higher precision crystal oscillator as the clock source.
The abbreviation for real-time clock is RTC (Real_TIme Clock). An RTC is an integrated circuit, commonly referred to as a clock chip.
The clock chip is a very important part of the clock. Most of the clock chips are produced by American DALAS company, which has the function of low current charging and low power consumption. The clock chip can time the year, month, day, second, hour, minute, and display the time at any time. There is also the role of compensation for the leap year. Many friends are unfamiliar with the clock chip, and do not know what the interface of the clock chip is. Let's take a look at it by Xiaobian.
First, the parallel interface
The MAXIM-DALLASDS12C887 series has now evolved many models.
Mainly several major manufacturers MAXIM-DALLAS, PHILIPS, Japan Seiko. Now many common rtc chips are imitation in China, and the price is good. It is good to use a place that is not very demanding.
Many common models can find the corresponding models here, including ds1302, ds1307, ds1337, pcf8563
Second, the serial interface
1.I2C interface
Phlilps PCF8563, PCF8583
EPSON's RX8025 has a built-in crystal oscillator with low error. More good
MAXIM-DALLAS DS1307
RICOH RS5C372, domestic Belling imitation model BL5372
Seiko's S-35390
Intersil X1288
The SD2000 series from Shenzhen Weifan Electronics Co., Ltd., crystal oscillator and battery are all built in, and the volume is large.
Third, three-wire interface
MAXIM-DALLAS DS1305, DS1302, of which DS1302 has related imitation products in China, and PTI's imitation model is PT7C4302.
Taiwan Hetai HT1380, HT1381
The real-time clock is the clock that the microcontroller clocks or the independent clock that can be accessed by the microcontroller. It can be obtained by external expansion chips, such as 1302, 1307, 12887, 3130, 12020, m41t81, 6902, 8025. There is a serial port on the parallel port, there is a battery to play with yourself, there is external power supply, see the actual needs of the design. These clocks use 32768Hz without exception. This is because they use the same timing IC core, lower power consumption, easier calibration, and 1Hz timing precision. Everyone has made different articles on this basis. Some of them have some stable crystal oscillators, some have some power backup schemes, some have different interfaces, some have a perpetual calendar, some have some alarms, some have...
3, there may be you mentioned (probably 430 series MCU), the internal integration of RTC module, requires external connection of 32768Hz. In this way, it can be timed independently, and the single-chip computer sleeps has nothing to do with its time management. The low-cost real-time solution saves a few hairs.
Principles and characteristics of the DS1302
The DS1302 is a trickle charge clock chip from DALLAS. In 2001, DALLAS was acquired by MAXIM. Therefore, we can see that the DS1302 data sheet has both the DALLAS logo and the MAXIM logo.
The DS1302 is a high-performance, low-power, real-time clock circuit with RAM that can time the year, month, day, week, hour, minute, and second. It has a leap year compensation function and operates from 2.5V to 5.5. V. The three-wire interface is used for synchronous communication with the CPU, and multiple bytes of clock signals or RAM data can be transmitted at one time in a burst mode. The DS1302 has a 31&TImes;8 RAM register for temporarily storing data. The DS1302 is an upgraded version of the DS1202 that is compatible with the DS1202, but adds dual-supply pins for the mains/backup power supply and provides the ability to charge the backup power supply with a fine current.
Control character representation of control byte DS1302. The most significant bit (bit 7) of the control byte must be a logic one. If it is 0, the data cannot be written to the DS1302. If bit 6 is 0, it means accessing the calendar clock data, and 1 means accessing the RAM. Data; Bit 5 to Bit 1 indicate the address of the operating unit; the least significant bit (Bit 0) if 0 indicates that a write operation is to be performed, and a value of 1 indicates that a read operation is performed, and the control byte is always output from the lowest bit.
When the input and output are on the rising edge of the next SCLK clock after the control instruction word is input, the data is written to the DS1302, and the data input starts from the low bit, bit 0. Similarly, the data of the DS1302 is read at the falling edge of the next SCLK pulse immediately following the 8-bit control instruction word, and the data is read from the lower 0 bits to the upper 7 bits.
Register DS1302 has 12 registers, 7 of which are related to calendar and clock. The stored data bits are in BCD format. The calendar, time register and its control words are shown in Table 1. In addition, the DS1302 has a year register, a control register, a charge register, a clock burst register, and a RAM-related register. The clock burst register can read and write all the contents of the registers except the charge register in one order. The DS1302 and RAM related registers are divided into two categories: one is a single RAM unit, a total of 31, each unit is configured as an 8-bit byte, and its command control word is C0H~FDH, where the odd number is a read operation. The even number is a write operation; the other is a RAM register in burst mode. In this mode, 31 bytes of all RAM can be read and written at one time, and the command control words are FEH (write) and FFH (read).
The DS1302 real-time clock chip is widely used in products such as telephone, fax, and portable instruments. His main performance indicators are as follows:
1, DS1302 is a real-time clock chip, can provide seconds, minutes, hours, dates, months, years and other information, and also the ability to automatically adjust the software, you can configure AM / PM to determine whether to use 24-hour format or 12-hour format .
2. Has 31 bytes of data storage RAM.
3, serial I / O communication mode, relatively parallel to save the use of IO port.
4, DS1302's working voltage is relatively wide, probably 2.0V ~ 5.5V can work normally.
5, DS1302 clock chip power consumption is generally very low, it works at a voltage of 2.0V, the operating current is less than 300nA.
6, DS1302 has 8 pins, there are two kinds of package, one is DIP-8 package, chip width (without pins) is 300mil, one is SOP-8 package, there are two widths, one is 150mil, one is 208mil
The DS1302 has shortcomings such as low clock accuracy, vulnerability to the environment, and clock chaos. The DS1302 can be used for data logging, especially for certain data points with special meanings, enabling data to be recorded simultaneously with the time at which the data appears. This kind of recording is of great significance for the analysis of the results of long-term continuous measurement and control systems and the search for the causes of abnormal data.
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