Design LED Chinese scrolling display using EDA
The Chinese character scrolling display designed by the traditional method usually needs to use the single chip microcomputer, the memory and the control logic circuit for the PCB (printed circuit board) board level system integration. Although this kind of scheme has more flexible support of single-chip software, due to the limitation of hardware resources, it is always difficult to avoid the cost of more R&D expenditure and longer market cycle due to the design change and upgrade in the future.
With the advancement of Electronic Design Automation (EDA) technology, a complete solution for the design of digital electronic systems based on programmable ASIC devices has received more and more attention, and systems based on EDA technology can be implemented on programmable ASIC devices. The new design method of chip integration is also rapidly replacing the traditional design method based on PCB board.
How to design electronic systems using EDA tools is a common concern. With the support of EDA tool software MAX+PLUSII, the design passed the compilation, adaptation and software simulation verification. Finally, it is proved by the hardware experiment loaded into the real experimental system.
In order to simplify the discussion, this paper only studies the problem of scrolling and displaying multiple Chinese characters on a single 8&TImes;8 LED light-emitting diode dot matrix.
Figure 1 shows a general-purpose hardware circuit designed to support scrolling display of multiple Chinese characters using ALTERA's 10K series FPGAs.
In the figure, the standard JTAG interface is connected to the parallel port of the PC to download the design data to the FPGA; the data line of the LED dot matrix is ​​driven by the I/O line string of the FPGA 300Ω current limiting resistor, and the sw line is directly driven by the FPGA. I/O line driver. The LED dot matrix adopts a scanning mode of operation, and the cyclic scan signal of the control sw line is active low, and the display data is active high.
Since ALTERA's 10K10LC84-4 chip has sufficient RAM resources inside, this design does not use external RAM.
In addition, the configuration EPROM in the figure is optional and only needs to be used when the Chinese character scroll display is required to run offline.
In order to display Chinese characters on the 8&TImes;8 LED light-emitting diode dot matrix, the Chinese character should first be represented as 8&TImes; 8 pixel dot map as shown in Fig. 2.
In FIG. 2, data0 to data7 are Chinese character pixel information sequentially sorted by columns, each having an 8-bit word length.
Then, the pixel information is extracted from the multi-Chinese characters in turn, and sequentially stored in the ROM, and a data sequence to be displayed is obtained. Further, by means of the addressing method to control the release process of the data sequence, the purpose of scrolling and displaying the multi-character information on the 8&TImes;8 LED light-emitting diode dot matrix can be realized. Figure 3 shows the principle of implementing scrolling display of multi-Chinese character information.
It can be seen from FIG. 3 that the address pointer that can locate the data to be displayed in the display data sequence at a certain time can be calculated by the following formula:
Addr=n+m (1)
Obviously, the value range of n should be 0~N, and it controls the scrolling speed of the Chinese character display; the value range of m should be 0~7, and it determines the scanning speed of the column switch sw of the LED dot matrix. Therefore, the control n scans the time of all the data to be displayed, and can adjust the scrolling speed of the Chinese character information; changing the repeated scanning period of m can improve the stability of displaying the complete Chinese character information on the LED dot matrix.
In addition, it should be pointed out that since the operation of equation (1) is implemented by hardware, the modulus of the address pointer addr should be taken as N, and in order to realize that all Chinese information is rolled over the LED dot matrix, 8 empty data must be added before the data N. byte.
According to the display principle given in Figure 3, we can construct the hardware implementation structure corresponding to it as shown in Figure 4.
Based on the principle shown in Figure 4, we designed a VHDL language program that describes the hardware capabilities of the FPGA core. This design uses a parametric model library from ALTERA's MAX+PLUSII PLD development tool and takes a structured description.
Here is the VHDL program we designed:
In the VHDL design, the initialization data of the ROM unit is provided by the display data file data.hex, and the data storage of the file is in accordance with the Intel HEX format. Since the display data directly extracted from Chinese characters is binary code, it cannot be directly used to generate data.hex files, so other EDA tools are needed to help process the data.hex file. The specific steps of processing the display data file data.hex are given below:
1. Extracting pixel information for a plurality of Chinese characters to form a sequence of data to be displayed arranged in order;
2. Using Heluo's universal programmer ALL03 or ALL07 application software, the data to be displayed is processed into binary data file data.bin in BIN format;
3. Using the single-chip emulator software of Wanli Company, convert the binary data file data.bin into the display data file data.hex of Intel HEX format.
Of course, we can also use the application software of the MCU emulator to directly process the display data file data.hex, but this requires software programming of the display data with binary code, so it is not as simple as the above method.
In order to verify the correctness of the design, we use the simulation simulator in the EDA tool software MAX+PLUSII to verify the simulation of the VHDL design of the compiled Chinese character scrolling display. The experiment proves that the Chinese character scrolling and display scanning are normal, that is, It is said that the FPGA core hardware works well and can correctly implement the design function.
In addition, the VHDL soft core design of the Chinese scroll display is also loaded into the real hardware system built according to Figure 1. The experimental verification of the hardware system also obtained the results consistent with the software simulation results.
Therefore, we can draw the following conclusions:
1. EDA technology can not only reduce the complexity and difficulty of digital electronic system design, but also significantly enhance the flexibility of design;
2. The combined application of multiple EDA tools helps to improve design efficiency and shorten design cycle;
3. The software simulation results obtained by using the EDA tool have the same importance and credibility as the traditional hardware experimental data.
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