AN1368 datasheet(13/34 Pages) MICROCHIP

13 / 34 page

 2011 Microchip Technology Inc.

DS01368A-page 13

AN1368

Frame Buffer Size

The size of the frame buffer is calculated as follows:

EQUATION 2:

Table 3 shows an example for the QVGA (320x240)

display. If the double-buffering technique is used, the

frame buffer requirement will double (see Appendix B:

“Double-Buffering”

for more information).

If the frame buffer is inside the display controller or the

smart display module, and if the RAM is fixed, the

maximum resolution that can be supported is limited.

Processing Power (MIPS)

The processing power required is application-specific.

It depends on how many graphic elements are

displayed on the screen and the complexity of the

graphic elements. More processing power is required

to draw complex shapes, such as a circle, bevel, text,

etc., rather than lines and rectangles. The processing

power requirements also depend on if a hardware

graphics accelerator is available and used. Processing

power requirements also depend on the update rate of

the screen elements. For many embedded graphics

applications, ≥ 16 MIPS processing power could be

sufficient. The best way to check the processing power

requirements is to evaluate using the standard

graphics development tools. (For more information on

development tools, see the “Development Tools”

section.

Configuration of Graphics Components

In Table 2, each configuration has its own advantages

and disadvantages.

Most often, the decision to use one or another

configuration is not influenced by the technical advan-

tages or disadvantages, but rather by a supply chain

advantage or the availability of components. The

designer must balance between optimizing a design to

meet the requirement and managing the supply chain.

Frame Rate VS. MIPS

Frame rate refers to the number of different frames that

can be displayed in a second. This is a good

performance index for display of a video, but not for an

embedded GUI application. In general, an embedded

application does not always change the entire screen,

instead it changes a part of the screen, like a button or

a check box. The amount of change depends on the

size of the changed widget. The update time also

depends on factors, such as if the change belongs to a

widget or an image. It is important to consider the

worst-case scenario on the planned application. Initial

calculation of frame rate and MIPS is important to get

the preliminary requirements for the system. In addition

to these calculations, it is recommended to evaluate

the system using development tools, such as

evaluation kits.

Frame Buffer (Bytes) = Total_number_of_pixels x

Color_Depth (in BPP)/8

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