STM32F469 datasheet(58/91 Pages) STMICROELECTRONICS

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Creating a graphical application with LTDC

AN4861

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DocID029237 Rev 2

4.8

Storing graphic primitives

Graphic primitives are basic elements (such as images or fonts) which can combined to

build the framebuffer content that is displayed.

Static data should be placed in a non-volatile memory. When the amount of data to store is

relatively low, the internal FLASH memory can be used. Otherwise, graphical contents

should be placed in external memories.

The STM32 microcontrollers offer parallel (FMC) or serial (QSPI) interface for external NOR

Flashes (see Table 3).

To build the framebuffer content, the DMA2D can directly read graphic primitives form a

parallel NOR Flash or a Quad-SPI Flash.

Refer to the application note Quad-SPI (QSPI) interface on STM32 microcontrollers

(AN4760) for more details on storing graphic content on QSPI memory.

4.8.1

Converting images to C files

To add graphic primitives to a user project, they should be converted to C or header files. In

order to do that, the user can use some specific tools allowing to generate C or *.h files.

Warning:

The user must convert images to C files respecting the

configured pixel input format described in Section : Pixel

input format on page 27. Some tools may generate C or *.h

files with red and blue colors swapped. To avoid this issue

(displaying an image with red and blue swapped), the user

can use the LCD image converter tool.

The LCD image converter is a very customizable free tool allowing to convert images to C

files and offering the possibility to generate the C file in the desired format. An example is

described in Section 6.2.5: Displaying an image from the internal Flash.

4.9

Hardware considerations

This section provides some hardware considerations for a graphic application. In general

two important hardware interfaces should be designed carefully: the LTDC interface and the

external memory interface (used for framebuffer) such as FMC_SDRAM or FMC_SRAM.

LTDC parallel interface

When the pixel clock is below 40 MHz (SVGA), a simple 3.3 V signaling can be used.

It is possible to reach 83 MHz with a parallel RGB if the load and the wire length are reduced

(for example to interface on the same PCB with on-board an LVDS transciver or HDMI

transceiver).

It is recommended to configure the LTDC GPIOs at the maximum operating speed

OSPEEDRy[1:0] = 11b. Refer to the relevant STM32 reference manual for a description of

the GPIOx_SPEEDR GPIO port output speed register.

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