Design of variable speed colored light controller using VHDL language

0 Introduction

Hardware Description Language (HDL) is relative to general computer software languages ​​such as C and Pascal. HDL is a computer language used to design hardware electronic systems. It describes the logical functions, circuit structures and connection methods of electronic systems. Designers can use HDL programs to describe the desired circuit system, specify its structural features and circuit behavior, and then use synthesizers and adapters to turn this program into gate-level or lower-level structural netlist files and download files that can control the internal structure of FPGA and CPLD and implement corresponding logical functions. VHDL (Very High Speed ​​Integrated Circuit Hardware description Language) is mainly used to describe the structure, behavior, function and interface of digital systems. Compared with other HDL languages, VHDL has stronger behavioral description capabilities, which determines that it has become the best hardware description language in the field of system design. Strong behavioral description capabilities are to avoid specific device structures. It is an important guarantee for describing and designing large-scale electronic systems from the perspective of logical behavior. In the literature, the author expounds on the application of EDA technology from different perspectives. It has the characteristics of powerful functions, strong description capabilities, good portability, short development cycle, and low cost. Even if the designer does not understand the structure of the hardware, he can carry out independent design. This paper uses Max+PlusⅡ provided by Alter Company as the platform to design a variable-speed colored light controller. It can implement the programming control scheme of modifying the flower pattern arbitrarily by changing the software without modifying the hardware circuit. It can control 16 LEDs to display in 8 patterns and 4 speeds in a cycle. The design is very convenient and the designed circuit has strong confidentiality.

1 Design Principle

When designing with VHDL, we should first understand that VHDL is an all-round hardware description language, including multiple design levels such as system behavior level, register transfer level and logic gate level. We should make full use of VHDL's "top-down" design advantages and hierarchical design concepts. The hierarchical concept is very useful for designing complex digital systems. It allows us to start with simple units and gradually build large and complex systems.

First, the system modules should be divided, and the functions of each module and the interfaces between the modules should be specified. The final design is divided into three modules: 16-way pattern light controller, four-frequency output divider, and four-choose-one controller. The four-choose-one controller selects clock signals of different frequencies from the divider and transmits them to the pattern light controller, so as to control the flashing speed of the lights and the change of patterns.

Below is the top-level module schematic diagram of this design as shown in Figure 1.

2 Submodules and their functions

(1) Four-frequency output divider. According to the requirement, there are 4 speed changes, each of which needs to display 8 patterns, so a three-bit counter and a 16-bit digital decoder are required. Secondly, there are 4 speed changes, but there is only one input clock signal, so the input clock signal needs to be divided. This design uses 2-division, 4-division, 8-division and 15-division to obtain 4 different frequency signals.

The program code of the binary frequency divider circuit is as follows:

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There are two schemes for designing a four-way frequency divider circuit: one is to connect two two-way frequency divider circuits in series (see Figures 2 and 3) to achieve four-way frequency divider; the other is to modify the program code of the two-way frequency divider circuit to achieve it, and make the following modifications:

Similarly, there are two solutions for the design of the eight-frequency division circuit: one is to connect two four-frequency division circuits in series to achieve eight-frequency division; the other is to modify the program code of the two-frequency division circuit. You only need to make the following modifications:

The 15-frequency division circuit is shown in Figure 4, and the simulation diagram is shown in Figure 5. The code is as follows:

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The top-level module schematic diagram of the four-frequency output divider is shown in Figure 6, and the simulation waveform is shown in Figure 7.

(2) Four-choice controller. The function of the four-choice controller is to select different clock signals from the frequency divider and send them to the color light controller to achieve the change of the flashing frequency of the color lights, as shown in Figures 8 and 9. The source code is as follows:

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(3) Colored light controller. The colored light controller circuit is the core of the entire design. It controls the output effect of the entire design, that is, the pattern changes. In the circuit, 1 represents the light on, and 0 represents the light off. Different combinations of 0 and 1 according to different rules represent different light patterns. At the same time, it can select different frequencies to achieve a variety of patterns and multiple frequencies. The program fully demonstrates the flexibility of designing circuits with VHDL, that is, the number of colored lights can be changed by changing the number of bits of the output variable in the program. As shown in Figures 10 and 11.

The code is as follows:

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3 Conclusion

Using VHDL language to design circuits has simple ideas and clear functions. Using Max+PlusⅡ to design circuits can not only perform logic simulation, but also timing simulation. Using PLD not only saves the trouble of circuit production, but also allows repeated hardware experiments, which is very convenient to modify the design, and the designed circuit has strong confidentiality. In short, the use of EDA technology makes the design of complex electronic systems simple and easy, and improves the efficiency of design.