STM32F479 datasheet(32/91 Pages) STMICROELECTRONICS

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Creating a graphical application with LTDC

AN4861

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DocID029237 Rev 2

As shown in the formula above, the required framebuffer size depends on the display

resolution and on its color depth.

It is not necessary that the framebuffer color depth (bpp) is the same than the display color

depth. For instance, an RGB888 display can be driven using an RGB565 framebuffer.

Note:

The required framebuffer size is doubled for double framebuffer configuration. It is common

to use a double buffer configuration where one graphic buffer is used to store the current

image while the second buffer used to prepare the next image.

Table 9 shows the framebuffer size needed for standard screen resolutions with different

pixel formats.

Framebuffer location

Depending on the required framebuffer size, it can be located either in an internal SRAM or

in an external SRAM/SDRAM.

If the internal RAM is not enough for the framebuffer, the user must use an external

SDRAM/SRAM connected to the FMC.

Consequently, the required framebuffer size will determine if the use of an external memory

is needed or not. The required framebuffer size depends on the display size and color

depth.

Locating the framebuffer in the Internal SRAM

Depending on the framebuffer size, it can be placed either in the internal SRAM or the

external SRAM or SDRAM.

Using an internal SRAM as a framebuffer allows the maximum performances and avoids

any bandwidth limitation issues for the LTDC.

Table 9. Framebuffer size for different screen resolutions

Screen resolution

Number of

pixels

Framebuffer size (Kbyte)(1)

1. The required framebuffer size is doubled for double framebuffer configuration.

8 bpp

16 bpp

24 bpp

32 bpp

QVGA (320 x 240)

76800

150

225

300

Custom (480 x 272)(2)

2. An example of a custom 480 x 272 display is the ROCKTECH embedded on the STM32F746 discovery kit

(32F746GDISCOVERY).

130560

128

255

383

510

HVGA(480 x 320)

153600

150

300

450

600

VGA (640 x 480)

307200

300

600

900

1200

WVGA(800 x 480)

384000

375

750

1125

1500

SVGA (800 x 600)

480000

469

938

1407

1875

XGA (1024 x 768)

786432

768

1536

2304

3072

HD (1280 x 720)

921600

900

1800

2700

3600

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