As the human machine interface (GUI) is growing in medical, industrial and consumer electronics, high integration, high-performance TFT LCD display schemes become an important part of electronic product design and development. In the case where there is no built-in liquid crystal controller, the single-chip microcomputer is often connected between the liquid crystal plate with the built-in controller, which is limited to the data transmission speed of the connection bus, which is difficult to support high display resolution. And picture quality.
STMicroelectronics launched a STM32F4x9 microprocessor based on the ARM Cortex-M4 kernel, making SVGA high-resolution and high quality display screen quality by the built-in LCD-TFT display controller and chrom-ARM graphics accelerator. This paper completes the hardware design of the LCD display around the STM32F4x9 microcontroller and introduces this hardware platform and STEMWIN software application development.
1 LCD display system architecture based on STM32F4x9
The performance of the liquid crystal display in the electronic system not only depends on the drive capability of the microcontroller built-in LCD TFT liquid crystal controller, which typically includes support for maximum display resolution, screen refresh speed, and pixel data format, which also depends on the data in memory and liquid crystal control. The transmission capacity between the unit and the flexibility of displaying image data processing.
1 .1 LCD display system based on STM32F4X9
The STM32F4x9 provides designers with an LCD display system architecture consisting of a bus controller including the ARM Cortex-M4 core, a chrom-ART graphics accelerator, a bus controller, and memory consisting of internal flash, RAM, and external SDRAM. Referring to FIG. 1, the Chrom-ART accelerator and the LCD-TFT controller can cooperate with the processing of the image, including pixel format conversion, two-layer image mixing, etc., and transmit display frame cache data in external SDRAM to the connection at LCD-TFT The controller's LCD screen.
Figure 1 STM32F4X9 LCD display system architecture
For example, the Chrom-ART accelerator can transmit the graphical elements stored in the internal flash to the internal RAM, and further create a display frame cache in the external SDRAM, and refresh the display content. The LCD-TFT LCD controller will then complete the image transfer from the external SDRAM to the LCD display.
1 .2 LCD-TFT controller structure and function
As an AHB bus controller, the LCD-TFT controller has two dedicated FIFOs to transmit two layers displayed images from the memory, and converted to the same Argb8888 color format from the independent pixel format conversion unit, thereby supporting RGB888, RGB565, ARGB1555, ARGB4444, L8, AL44, Al88 are included in a variety of pixel formats. As shown in FIG. 2, the mixing unit is responsible for mixing the two layers of the same format together along with the background color, and transmitting the final display data to the LCD screen via the jitter unit. The data transfer between the LCD TFT controller and the liquid crystal screen is completed by 24-bit data R [07], G [07], B [07], row column synchronization signal LCD_HSYNC, LCD_VSYNC, clock signal LCD_CLK, and data enable signal LCD_DE.
Figure 2 LCD TFT controller structure and function
1 .3 chrom-ART graphics accelerator structure and function
Another AHB bus controller CHROM-ART graphics accelerator in the system is a dedicated graphic display processing DMA. It can copy some or overall the source image to the target image, and simultaneously complete the conversion of the image pixel format. As shown in FIG. 3, the Chrom-ART accelerator can also complete the hybrid processing of the foreground and background images and allow the pixel format of the specified output image. Based on the strong support and flexibility of the Chrom ART accelerator, the CPU load of the image processing will be greatly reduced.
Figure 3 CHROM ART graphics accelerator structure and function
2 STM32F4X9 LCD-TFT interface hardware design
The STM32F4x9 LCD-TFT controller provides a parallel 24-bit RGB digital interface (LCD_R [07], LCD_G [07], LCD_B [07]), row synchronization signal LCD_HSYNC and LCD_VSYNC, and clock LCD_CLK and data enable signal LCD_DE, it can be conveniently Connect directly to a variety of different LCD display.
A liquid crystal display extension of 24-bit and 18-bit width RGB interfaces is achieved on STM32429i EVAL and STM32439i Eval evaluation boards, respectively. It should be noted that when the interface width of the liquid crystal display is required to be less than 24 bits, when RGB 565 or RGB666, the high data line of each color must be connected to the expanded LCD screen. For example, as shown in Figure 4, R [27], G [27], G [27], G [27], B [27] signals of the liquid crystal controller are respectively R [05], G [05], respectively, in the STM32439ieval evaluation board, respectively. B [05] is connected.
Figure 4 STM323X9I EVAL LCD hardware interface design
It can be seen from the STM32F4x9 controller, which can be seen very conveniently constructed from a liquid crystal display hardware system composed of an external SDRAM that is directly connected to the TFT LCD controller and an external SDRAM of the FMC.
3 Graphic Stack Software Library STEMWIN
The free STEMWIN graphics package is the cooperation development results of semiconductor and segger, based on Segger's market-tested EMWIN embedded graphics software package. Stemwin uses the STM32F4 microcontroller built-in LCD-TFT controller and the Chrom-ART accelerator to significantly improve graphics processing performance, and equipped PC design tools support high performance GUI development.
The Stemwin graphics package supports JPG, GIF, and PNG decoding, and the widgets carrying the package make the establishment of a simple GUI faster, convenient, and support professional development tools Guibuilder to achieve simple drag and drop actions.
Conclusion
Based on the built-in LCD-TFT controller, the Chrom-ART graphics accelerator, and the FMC external SDRAM controller, the STM32F4X9 microcontroller for semiconductors makes it easier and flexible to build the LCD display system in the mobile portable device.
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Source: Wiku Electronic Market Network
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