STM32F469 datasheet(9/91 Pages) STMICROELECTRONICS

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Display and graphics overview

•

The framebuffer is a volatile memory used to store pixel data of the image to be

displayed. This memory is usually called the graphic RAM (GRAM). The required size

of the framebuffer depends on the resolution and color depth of the display. See

Section 4.2.1: Framebuffer memory size requirements and location for more

information on the required size of the framebuffer.

–

Double buffering is a technique which uses double framebuffers to avoid

displaying what is being written to the framebuffer.

•

The display controller is continuously “refreshing” the display, transferring the

framebuffer content to the display glass 60 times per second (60 Hz). The display

controller can be embedded either in the display module or in the MCU.

•

The display glass is driven by the display controller and is the responsible to display the

image (which is composed of a matrix of pixels).

A display is characterized by:

–

Display size (resolution): is defined by the number of pixels of the display which is

represented by horizontal (pixels number) x vertical (lines number).

–

Color depth: defines the number of colors in which a pixel can be drawn. It is

represented in bits per pixel (bpp). For a color depth of 24 bpp (which can also be

represented by RGB888) a pixel can be represented in 16777216 colors.

–

Refresh rate (in Hz): is the number of times per second that the display panel is

refreshed. A display shall be refreshed 60 times per seconds (60 Hz) since lower

refresh rate creates bad visual effects.

Display module categories

The display modules are classified in two main categories, depending on whether they

embed or not an internal controller and a GRAM.

•

The first category corresponds to the displays with an on-glass display controller and a

GRAM (see Figure 2).

•

The second category corresponds to the displays with an on-glass display with no main

controller and that have only a low-level timing controller.

To interface with displays without controller nor GRAM the used framebuffer may be

located in the MCU's internal SRAM (see Figure 3) or located in an external memory

(see Figure 4).

Figure 2. Display module with embedded controller and GRAM

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