STM32F479 datasheet(66/91 Pages) STMICROELECTRONICS

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LTDC application examples

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Figure 35. Backlight controller module

6.2.2

How to check if a specific display size matches the

hardware configuration

This section assumes that at this stage the user has a desired display size of

480 x 272 @ 60Hz and with a 24 bpp color depth and that the next step is to select the right

hardware configuration.

Desired display panel

The desired display is the ROCKTECH RK043FN48H-CT672B display:

•

Display resolution: 480 x 272 pixels with LED backlight and capacitive touch panel.

•

Display interface: 24-bit RGB888 (in total 28 signals).

Determining framebuffer size and location

Depending on its size and on the internal available SRAM size, the framebuffer can be

located either in the internal SRAM or in the external SDRAM. The total embedded SRAM

size for the STM32F746NGH6 MCU is 320 Kbyte where SRAM1 (240 Kbyte) can be used

(see Figure 10: LTDC AHB master in STM32F7x6, STM32F7x7, STM32F7x8 and

STM32F7x9 smart architecture).

The framebuffer size is calculated in the following way:

•

For 24 bpp

–

framebuffer (Kbyte) = 480 x 272 x 3 / 1024 = 382.5

•

For 16 bpp

–

framebuffer (Kbyte) = 480 x 272 x 2 / 1024 = 255

•

For 8 bpp:

–

framebuffer (Kbyte) = 480 x 272 / 1024 = 128

So based on these results, the required framebuffer size is about 128 Kbyte for 8 bpp. In

that case, the framebuffer can be located in the internal SRAM1 (240 Kbyte). This is not

valid for a double framebuffer case as the size of 128 x 2 Kbyte exceeds the internal SRAM

size.

For the 16 bpp color depth and in a double framebuffer configuration, the required

framebuffer size (2 x 255 Kbyte) exceeds the internal SRAM size, so using an external

SRAM or SDRAM is a must for this configuration.

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