Design of decimal counter based on MAX+PLUSⅡ

Abstract: MAX+PLUSⅡ software is an easy-to-learn and easy-to-use design and development environment, and its application in digital circuit design is becoming more and more extensive. Based on this, this paper first introduces the commonly used design input methods of MAX+PLUSⅡ software; then designs a decimal counting circuit, and simulates the circuit with MAX+PLUSⅡ software; finally, the circuit diagram is cut into the experimental box to verify the correctness of its function.
Keywords: MAX+PLUSⅡ; VHDL; Counter

O Introduction
MAX+PLUSⅡ development system is an easy-to-learn and easy-to-use fully integrated design and development environment. Currently, version 10.0 has been released. Compared with LATTICE's iSPEXPERT and XILINX's FOUNDATION, this software has the characteristics of simple use, flexible operation, more supported devices, and flexible and changeable design input methods. Commonly used design input methods are as follows:
(1) Graphic design input: MAX+PLUSⅡ's graphic design input is easier to use than other software because MAX+PLUSⅡ provides a wealth of library units for designers to call, especially the mf library provided in MAX+PLUSⅡ contains almost all 74 series devices, and the prim library provides all discrete devices in digital circuits. Therefore, as long as you have knowledge of digital circuits, you can use MAX+PLUSⅡ to design CPLD/FPGA without much learning.
(2) Text editing input: MAX+PLUSⅡ's text input and compilation system supports three input methods: AHDL language, VHDL language, and VERILOG language.
(3) Waveform input method: If you know the input and output waveforms, you can also use the waveform input method.
(4) Mixed input method: MAX+PLUSⅡ design and development environment supports mixed editing of graphic design input, text editing input, and waveform editing input.

1 Design of decimal counter
The structure of the decimal counting circuit is shown in Figure 1. It is mainly composed of an anti-jitter circuit, a BCD code counter and a seven-segment decoder. The circuits of each part are introduced as follows:


1.1 Switch anti-jitter circuit
The button will vibrate for several milliseconds from the initial pressing to the stable contact. The same problem also occurs when the key is released, as shown in Figure 2. The input time ta varies from person to person, and the general switch ta is <100ms. The purpose of setting the switch anti-jitter circuit is: press the key once and output a pulse. That is, the actual output of the switch is used as the input of the switch anti-jitter circuit, and the output of the switch anti-jitter circuit is the ideal output shown in Figure 2.


1.2 BCD code counter
The BCD code counting circuit used in this design is composed of 74160, which is a decimal synchronous counter (asynchronous clearing). In its function table, when the four input terminals of LDN, ENT, ENP, and CLRN are all connected to a high level, the rising edge of the CLK input pulse is counted, and the 8421 code is output by QA-QD.

1.3 Seven-segment decoder circuit
The seven-segment decoder circuit used in this design is composed of 7447 and an external common cathode digital tube. The 7447 seven-segment decoder decodes the BCD8421 code into the seven-segment digital display code required by the digital tube.
In summary, the designed decimal counter circuit is shown in Figure 3.



2 Simulation of decimal counter
Open the PC interface MAX+plusⅡ software, input the circuit diagram of Figure 3; select the menu File＼Project＼Set Project to Current File, and then select the menu MAX+plusⅡ＼complier to edit the current graphic file; simulate Figure 3, and the simulation result is shown in Figure 4. It can be seen from Figure 4 that the designed circuit (Figure 3) meets the logical requirements of the decimal counter.


Use the Byte Blaster download cable to connect the PC parallel port and the experimental box J1 (JTAG), and turn on the power switch of the experimental box. Select the menu item MAX+plusⅡ＼Programmer, click the Program button, and start downloading the program. Turn on the power switch of the experimental box and press K52 continuously. The LED1 of the digital tube will change from 0 to 9 in sequence, which meets the logical requirements of the decimal counter.

3 Conclusion
MAX+PLUSⅡ is a revolution in the field of electronic design. Its application is becoming more and more extensive. The application of MAX+PLUSⅡ in experimental teaching is not only to improve the design efficiency, but more importantly to cultivate talents who are adaptable to innovation and entrepreneurship, so as to adapt to the competition and development of the electronic industry.