Introduction Digital clocks have become the dominant direction of clock design and are widely used in real-time control systems. The digital clock is essentially a counting circuit for counting standard frequencies, and is usually composed of a crystal oscillation circuit, a frequency dividing circuit, a time counting circuit, a decoding driving circuit, and the like. Here, an electronic clock system design scheme is proposed. The AT89S52 single-chip microcomputer is used as the control core, and the PCF8563 clock/calendar device and the HS12864 liquid crystal display are realized through hardware design and software programming.
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2 Introduction to PCF8563 Figure 1 shows the internal structure of PCF8563. The PCF8563 includes 16 8-bit registers, an auto-incrementable address register, a built-in 32.768Hz oscillator (with an internally integrated capacitor), and a divider (used to provide the source clock to the RTC real-time clock). Program clock output, timer, alarm, brownout detector and 400 kHz I2C bus interface.
All 16 registers are designed as addressable 8-bit parallel registers, but not all bits are useful. The first two registers (memory addresses 00H, 01H) are used for control registers and status registers, where memory addresses 02H to 08H are used for the clock counter (second to year counter), and addresses 09H to 0CH are used for the alarm register (defining the alarm condition). The address ODH controls the output frequency of the CLKOUT pin, and the addresses OEH and OFH are used for the timer control register and the timer register, respectively. Second, minute, hour, day, month, year, minute alarm, hour alarm, day alarm register, encoding format is BCD, week and week alarm registers are not encoded in BCD format.
3 system hardware design Hardware circuit design includes PCF8563 clock, calendar device and AT89S52 microcontroller interface circuit, HS12864 liquid crystal display circuit and keyboard circuit. The AT89S52 is a low power, high performance CMOS 8-bit microcontroller with 8 KB in system programmable Flash memory; manufactured using high density nonvolatile memory technology and fully compatible with T industry 80C51 product instructions and pins: on-chip Flash allows program memory to be programmable in the system and also for conventional programmers. The sleek 8-bit CPU and in-system programmable Flash provide a highly flexible, ultra-efficient solution for many embedded control applications.
The PCF8563 uses a 32.768 kHz programmable clock output frequency. The I2C bus is a serial bus consisting of a data line SDA and a clock SCL that can transmit and receive data. The data is transmitted bidirectionally between the MCU and the PCF8563 with a maximum transfer rate of 100 Kb/s. The advantages of the FC bus are simple and efficient. Because the interface is directly above the component, the I2C bus takes up very little space, reducing board space and device pins, reducing cost. Figure 2 shows the interface circuit between PCF8563 and AT89S52 MCU. The SCL of PCF8563 is connected with pin P14 of MCU. SDA is connected with P15 of MCU to realize the reading of time and date.
Figure 3 shows the HS12864 liquid crystal display circuit. In conjunction with the programming and debugging of the single-chip software program, the clock information in the PCF8563 is output from the P01 to P07 ports to the liquid crystal display, and the display of time, date and other data is completed.
4 system software design System software mainly completes the system initialization and system control, namely: initialization crystal oscillator, I / O port, timer and read data in PCF8563, liquid crystal display program. During this period, the keyboard is scanned to determine if there is a key press, and if there is a key press, the corresponding operation is performed. The C language program for reading the data in PCF8563 is as follows:
5 Conclusion This paper introduces the design and implementation of the electronic clock system using AT89S52 microcontroller as the main control device. When designing the electronic clock system, the PCF8563 clock/calendar device is used, which is powered by a 3.3 V DC power supply, which simplifies the hardware circuit and improves the system reliability. The HS12864 liquid crystal display can accurately display the time. The practical application proves that the electronic clock has simple operation, high accuracy, small volume, low power consumption, and good anti-interference performance.
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