stm32f4 tft lcd example quotation

The STM32 LTDC has a peripheral called LTDC LCD TFT Display Controllerwhichprovides a digital parallel interface(DPI) for a variety of LCD and TFT panels. It sends RGB data in parallel to the display and generates signals for horizontal and vertical synchronization (HSYNC, VSYNC), as well as pixel clock (PCLK) and not data enable (DE) signals:

In this example I use the display on the STM32F429-Discovery board, which is driven by the ILI9341 display controller. The ILI9341 can drive a QVGA (Quarter VGA) 240×320 262,144 colors LCD display. The controller can be configured via SPI (or parallel interface, depending on the panel settings) to use a digital parallel 18 bit RGB interface (since only 6 lines per color channel are wired on the board to the LTDC). Since the display pixel format is less than 8 bit per channel (RGB666 in this case), the RGB display data lines are connected to the most significant bits of the LTDC controller RGB data lines:

Before enabling the LTDC we must configure the clock system. The LTDC uses a specific clock LCD_CLOCK to generate the pixel clock signal and it must be configured and enabled during the system initialization phase:

To display an image we must convert an image file to an array (possibly a const one, so it can be stored in flash memory) of bytes. To do this I used LCD image converter, a simple but powerful application that can convert a file to a variety of different pixel formats:

The second layer can be enabled as well and its contents drawn on top of layer 1. LTDC can manage transparency using the values in the LTDC_LxCACR Layer x Constant Alpha Configuration Register and LTDC_LxBFCR Layer x Blending Factor Configuration Register: here I used a constant alpha of 255 to obtain a 100% opacity (the value in the constant alpha register is divided by 255 by hardware so for example a value of 128 represents an alpha value of 0.5). Since the layer window is smaller than the display area the default layer background color is set to a transparent black (otherwise the default layer background color is used if the layer window is smaller than the display). The image is 110 x 110 pixels and the pixel format is ARGB8888 (the alpha channel is used to draw transparent pixels). Note that the LTDC_LxCBLR and LTDC_LxCBLNR registers are configured according to the image size: the LTDC always starts fetching data from the address defined in the LTDC_LxCFBAR register. I added the following lines of code to the LTDC_init() function to configure and enable layer 2:

In this example the framebuffers have a RGB888 color depth and for a 240×320 display that makes 225 KiB of memory for each buffer (3 bytes per pixel x 240 x 320 pixels) so they must be stored in external SRAM (the STM32F429I-DISCOVERY has a 64Mbit external SRAM so we’re good). The FMC Flexible Memory Controller has to be initialized and the address of the two frame buffers has to be configured. Drawing on the framebuffer is a matter of writing the right bytes in order to change the color. Once all pixels are drawn (bytes are written) the buffers are switched and the code can draw the next frame:

so im trying to make a frequency counter with a nucleoSTM32F429zi and i have a few issuse firstly im using a PWM output through a low pass filter to make a sine wave. that works fine however at the end of the project i have to desplay the frequance on an LCD this is where my problems i have an LCD connected properly. but when the PWM is active there is no output to either putty or the LCD i am also unable to send anymore than a single character at a time and i need a string to show the frequancy. please advise me on what is wrong

First of all, the initialization sequence: each TFT panel has its own specific settings, so my best bet was to copy the init sequence from the Cube BSP, as many of the values were quite off (e.g. the VCOMs).