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Digital Clock (Single Chip)
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  • Updated: 2020-01-31
  • Posted by : Xue Xiaochan
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  • Digital Clock (Single Chip)
  • Digital clock 1-a monolithic computer is a monolithic microcomputer. (Single-Chip Microcomputer), is a set of CPU, RAM, ROM,
    Microcontroller with timing, counting and multiple interfaces. It is small in size, low in cost, and powerful in function, and is widely used in intelligent products and industrial automation. The 51 single-chip microcomputer is the most typical and representative one among the single-chip microcomputers. This graduation design has achieved the ability to learn, design, and develop soft and hard through its learning and application.
    Second, the system consists of AT89C51, LED digital tube, buttons, light-emitting diodes, etc., which can realize the functions of time adjustment, timing setting, and output. The function selection of the system is completed by SB0, SB1, SB2, SB3, SB4. Of which SB0
    For time calibration, timer adjustment function key, press SB 0 to enter the adjustment state. SB1 is a function switching key. First push
    SB1 enters one, two and three timing time setting prompt procedures in sequence, press SB3 to enter the timing adjustment state of each channel. When the time is up, the diode lights up. It goes off after the off time. If you do not enter, continue to press the SB1 key, enter the time in sequence
    ? year Proofreading, ? month Proofreading, ? day Proofreading, ? Time Proofreading, ? Minute Proofreading, ? second Bit proofing status. No matter what state it is in, pressing SB2 can change the adjusted bit by 1 without increment. After the setting of each preset amount is completed, the system stores all the settings in RAM and presses SB1 to exit the adjustment state. After power on, the system automatically enters the timing state, starting at ?. 00? Time 00? Minute. SB4 is the year, month and day display conversion key, which can make the original display of hours, minutes and seconds display the year, month and day.
    Third, the circuit principle analysis
    1. Display principle See Figure 1 for the schematic diagram. Hours, minutes, and seconds are displayed by six common cathode digital tubes. 8 data lines for port P0
    P0.0 to P0.7 are respectively connected to the two ABCD ports decoded by CD4511, and P2.0 to P2.2 of P2 are connected through resistors
    R10 to R13 are connected to the bases of VT1 to VT3. In this way, the high and low BCD of a memory cell are sent through the P0 port.
    Display the code. Send the scan strobe code to turn on LED1 to LED6 through P2 port, and the data to be displayed will be displayed in the digital tube. The code output from port P0 is the BCD code, and the code output from port P2 is the bit selection code. This is the principle of scan display.
    .
    2 Keyboard and Reading Principle The keyboard is the main device for people to interact with microcomputers. Reading keys can easily cause misoperation. Software debounce can be used to deal with it. When the contacts of the software are closed and opened, jitter will occur. At this time, the logic level of the contacts will be unstable. If not properly handled, it will cause wrong key commands or Repeated execution, here software delay method is used to avoid jitter, the delay time is 20ms.
    3 Implementation of the combo function When a key is pressed, the corresponding function key interpretation program is executed. If the operator does not release the key, the corresponding function will be executed repeatedly, as if it is performed continuously. Here we use a software delay of 250ms, When the button is not released then ...
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