TFT display.LTDC is the interface through which Lcd-Tft Display Controller,mcu connects the LCD screen, and mcu sends the display data to the lcd-tft screen through this interface.

LTDC belongs to DPI (display pixel interface, display Pixel Interface, also known as RGB Interface). It constantly sends image data to the display (TFT LCD screen). The LCD screen does not need to have video memory, but there is a MCU side (on-chip RAM or extended RAM).

The pixels on the LCD screen are displayed line by line, scanned to the last line, and then back to the first line, much like the working mode of the VGA monitor.

Display scanning mode: starting from the top left of the screen, scanning point by point from left to right, scanning one line of electron beam back to the starting position of the second line on the top left of the next line of the screen, and blanking the electron beam, that is, cutting off the reverse electron beam, that is to say, there is a certain clock cycle for line blanking, and at the end of each line, the line is synchronized with the line synchronization signal: in order to make the display consistent with the shooting picture. The scanning frequency and phase should be consistent, so the synchronous signal.

All the lines are scanned to form a frame, and the field signal is synchronized and scanned back to the upper left of the screen.

The LTDC has four control signals: four control signals (pixel clock LCD_CLK, horizontal synchronization HSYNC, vertical synchronization VSYNC, data effective DE) and three RGB data signals (8-bit x 3). Communication is controlled by clock signal.

If the blue box corresponds to these signals, two green signals DISP controls whether the TFT screen is dormant, CTRL controls whether the TFT screen is displayed, and LCD_BL_CTRL controls the output of the power chip STLD40D, which is effective when it is high, so that the output LCD_BL_A (anode) and LCD_BL_K (cathode) are turned on, and the backlight of the TFT panel is turned on, which requires a high level in order to make the LCD screen work normally. The two signal lines of LCD_BL_CTRL and LCD_DISP are not LTDC “standard”, but are “unique” of LCD modules. Different modules may have different control signals, so the corresponding GPIO needs to be specially configured with CUBEMX.

When the LCD_DE is high, the LTDC output data to the LCD panel is valid (that is, after the LCD_DE becomes higher, the output data on 24 data lines such as LCD_R [7:0] is valid).

LTDC supports 2 Layer, and each Layer corresponds to a video memory, that is, an image. LTDC can overlay two images, layer1 at the bottom and layer2 at the top. The two layers can be enabled separately, can be used alone, or can be superimposed together.

If the layer1 remains still and the layer2 keeps changing the relative position, what you can see is the above image moving on the background image.

Each layer has an active “window”, which is the specific location and size of the image, that is, the Active display area in figure 7.

The size of the window can be equal to the size of the layer (full screen), or it can be smaller than the layer. For example, when you only need to display a picture with a size of 1max 4, you can define a window with a size of 1max 4 to display the picture, and the corresponding video memory only needs the size of 1max 4 to save memory. And the display position of the picture can be adjusted dynamically.