Design of Decimal Calculator System Based on AT89C51 Single Chip Microcomputer

This design is a decimal calculator system design based on the AT89C51 single-chip microcomputer. It can complete the keyboard input of the calculator, perform simple arithmetic operations of addition, subtraction, multiplication and division of 4-bit unsigned numbers, and display the results accordingly on the LED. In terms of hardware, from the functional considerations, the AT89C51 single-chip microcomputer with rich internal storage resources is first selected, and the input adopts a 4×4 matrix keyboard. The display adopts a 4-bit 7-segment common anode LED dynamic display. In terms of software, the system design is carried out from the analysis of calculator functions, flow chart design, to program writing. Here I recommend you to read the ten-day learning single-chip microcomputer.

　　0 Preface

　　This system uses AT89C51 single-chip microcomputer as the controller to realize the four-digit "+", "-", "*", "/" operation. The operation result is displayed through the digital tube and has a clearing function. AT89C51 has the following features: 40 pins, 4k BytesFlash on-chip program memory, 128 bytes of random access data memory (RAM), 32 external bidirectional input/output (I/O) ports, 5 interrupt priority levels, 2-level interrupt nesting interrupts, 2 16-bit programmable timer counters, 2 full-duplex serial communication ports, watchdog (WDT) circuit, and on-chip clock oscillator.

　　1 Overall design plan

　　1.1 System composition and working principle

　　This system is based on the 51 single-chip microcomputer as the main control core, and is combined with a matrix keyboard, crystal oscillator, and LED display tube module. Its working process is: first, the storage unit is initialized, the initial value and keyboard scan are displayed, the key position is determined, and the key value is obtained. The single-chip microcomputer stores the data and processes and converts it accordingly, and then sends it to the digital tube for dynamic display. The calculation result is sent to the digital tube for dynamic display. This design can only perform calculations with a result of no more than four digits, and its functions are as follows:

　　(1) The numeric keys "0" to "9" are displayed using digital tubes.

　　(2) Addition operation: Both the addend and the augend cannot exceed 9999, and the final result of the addition cannot exceed 9999.

　　(3) Subtraction operation: The normal logic of subtraction operation is to subtract a larger number from a smaller number. This calculator is also the same and can only perform normal logic operations. For example, if you want to subtract a larger number from a smaller number, add the resulting negative number to 535 to get the corresponding result. In other words, if you want to subtract a larger number from a smaller number, subtract 535 from the result to get the correct result for a negative number.

　　(4) Multiplication operation: As with the above method, the calculation result cannot exceed 9999. If overflow occurs, only the last three digits of the result will be displayed.

　　(5) Division operation: The divisor and dividend cannot exceed 9999, and only the integer part of the calculation result is displayed.

　　(6) Equal key: The calculation result will be displayed only when the equal key is pressed; otherwise, the previous number will be displayed.

(7) Reset function: When the program is unstable or an error occurs, use the reset key to return to the initial state. You can also use the reset key to reset.

　　2 System Hardware Design

　　2.1 Overall design of system hardware

　　This system consists of a keyboard matrix and an LED display tube. The keyboard inputs key values, and the LED display tube displays the current key presses and results. The overall hardware design diagram 1 is as follows:

　　2.2 Matrix scan displays the current key module

　　Use the P0 port P0.0 - P0.7 of the AT89S51 microcontroller to connect to the a - h segments of a seven-segment digital tube, and the common end of the digital tube is connected to the power supply. The matrix scan displays the current key module as shown in Figure 2. 

　2.3 Keyboard Layout Module

　　Working principle of matrix keyboard: The keyboard layout of calculator is shown in Figure 3: It is generally composed of 16 keys. In the single-chip microcomputer, one P port can be used to realize the functions of 16 keys. This form is also the most commonly used in single-chip microcomputer systems.

　3 System Software Design

　　3.1 System software overall design

　　The software flow of this system is shown in Figure 4.

　3.2 Display program modules

　　The display program calculates the thousands, hundreds, tens and units of the value to be displayed, outputs the value through the P0 segment selector, and realizes dynamic display through the bit selectors P3^3, P3^4, P3^5 and P3^6.

　　LED digital tube, realize the display of four-digit decimal number by seven-segment digital tube. The value of key and calculation result is displayed by segment selection. Since this hardware design adopts common anode connection, the corresponding segment code table is as follows 3.3 Keyboard scanning module

　　This keyboard scanning program uses the row-column flip method to scan the keyboard, that is, first set the row to 0, read the column value, and store it in variable 1, then set the column to 0, read the row value, and store it in variable 2. Adding variable 1 and variable 2 is the key value corresponding to the key. The following table shows the key values ​​corresponding to the corresponding keys.

　　This calculator is a calculator system based on the 51 series single-chip microcomputer. It is designed to perform simple arithmetic operations. Under the existing hardware conditions, it can only perform operations with results not exceeding four digits. It can realize the calculation functions of addition, subtraction, multiplication and division, the function of clearing numbers, and the reset function of the system.