introduction
A large number of nonlinear devices such as power electronic components are put into use in the power system, which makes the harmonic pollution of the power grid bring potential safety hazards to the power grid and electrical equipment. Therefore, the harmonics are detected in real time to accurately grasp the harmonic status of the system. It is necessary to prevent the harm of harmonics and maintain the safe operation of the power grid. The T6963C has bit operation commands. On the display of some characters, if the bit operation commands are used, the procedure is simple and easy to implement, that is, just call the bit operation command (0xfe) function after setting the display address. The design has completed the menu display of harmonics and the dynamic display of harmonic spectrum lines, which laid the foundation for the analysis of harmonic data in the future.
This design is the display part of the harmonic detector. The grid harmonic detector intuitively displays the harmonics (amplitude and frequency) of different frequencies, which can provide harmonic researchers with reliable harmonic data so that Good analysis and governance. DSP has the advantages of fast processing speed and powerful functions. The design uses TMS320F2812 as the control chip and HS12864 liquid crystal display module as the display device, which realizes the menu display of harmonic detection data and the display of harmonic spectrum lines. In order to solve the timing matching problem between the fast DSP chip and the slow liquid crystal display device, the F2812's rich I / O ports are used to realize the timing control and data communication with the HS12864, and the power between the high speed DSP and the slow liquid crystal module is solved. Ping conversion issues, and interface synchronization issues.
1 TMS320F2812 features
TMS320F2812 is the latest digital signal processor from TI. This device is a fixed-point digital signal processor based on the TMS320C2xx core. A variety of advanced peripherals are integrated on the device, which provides a good platform for the realization of motors and other applications. At the same time, the codes and instructions are fully compatible with the F24x series, thus ensuring the continuity of the project or product design. The chip uses a high-performance 32-bit central processor, Harvard structure, high-performance static CMOS technology, the main frequency can be up to 150MHz (clock cycle up to 6.67ns); with an external memory interface, can expand up to 1MB of space. There are 18KRAM, 128kflash memory, 128-bit key in the chip; there are rich on-chip peripheral devices such as timer, event manager, SPI, SCI, CAN, AD and so on.
2 HS12864 LCD display features
The biggest feature of T6963C is that it has a unique hardware initialization setting function. The parameters required by the display driver such as the duty cycle, the number of bytes / line transmitted by the driver, and the font of the characters are all set by the pin level. almost done. The implementation of font selection is to selectively transmit one byte of 8-bit font data in the display data transmission process. T6963C control series LCD has selected FS0 = 0, FS1 leads to the MCU interface, that is, FS, the user through FS Connect high or low to achieve 6 & TImes; 8 or 8 & TImes; 8 font selection. T6963C has built-in 128 kinds of 5 & TImes; 8 dot matrix ASCII character library CGROM, the character code is 00H ~ 07H, and allows the user to develop a user-defined character 8 × 8 dot matrix font library CGROM in the display memory. While using the internal CGROM, it can also support CGRAM, character codes are defined in 80H ~ FFH. T6963C can manage 64k display storage area, only 32k of memory on the actual module. T6963C divides the 32k memory into text display, graphic display, text attribute area or custom character library area.
3 hardware interface design
TMS320F2812 has two ways to access the LCD module: bus mode and I / O port mode. Because the processing speed of the LCD module is much slower than that of the DSP, to match the speed of the two, a certain delay must be added to meet the requirements. Therefore, the I / O method is adopted in this design, and the digital I / O of the DSP is used. To control the LCD module. The working voltage of the digital I / O port of the TMS320F2812 chip is 3.3V, and the working voltage of the liquid crystal module is 5V. In order to ensure the normal operation of the liquid crystal and the DSP chip will not be burned due to the excessive pin voltage, the two should be Connected to the level converter to achieve level conversion, because the system only writes signals to the liquid crystal module, as long as the voltage conversion from 3.3V to 5V is sufficient, this design uses two 74HCT245 as the level conversion chip.
The design uses 11 I / O ports of DSP, namely GPIOA0 ~ GPIOA2 (PWM1 ~ PWM2), GPIOB0 ~ GPIOB7 (PWM7 ~ T4PWM), through level conversion devices, they are respectively with LCD C / D, / RW , / CE, DB0 ~ DB7 pins are connected. As shown in Figure 1, the writing operation of the liquid crystal can be realized by setting GPIOA0 ~ GPIOA2 high and low. The system only writes to the liquid crystal, so the / RD pin of the liquid crystal is directly high, and the LCD FS The pin is directly connected to low (ground) to display the 8 × 8 font. The / RST end is connected to the Capacitor and resistor, and then to the ground and + 5V power supply respectively, V0 is connected to the potentiometer and negative pressure, used to adjust the LCD screen. Display contrast.
4 Realization of spectral line display
The idea adopted in this paper is: grid the LCD screen and divide each vertical 8-byte row into a group, then the vertical 64-byte row is divided into 8 groups. In this way, the vertical position changes from determining which line is located in the 64-byte line to determining which line is located in the 8 characters, so that the entire screen can be regarded as a small square consisting of 8 lines and each line has a total of 16 Filling the grid with Chinese characters or character codes can realize the display of Chinese characters or characters. In this way, for a liquid crystal with a specification of 128 × 64 dot matrix, one screen can display 32 16 × 16 Chinese characters or 128 8 × 8 characters.
5 Summary
This article uses the rich I / O ports of TMS320F2812, plus a delay program, which solves the problem of timing sequence matching with the slow-speed LCD module, and thus designs the interface circuit of the two. In the design of the software, the LCD screen is gridded according to the characteristics of the dot matrix graphic LCD display.
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