AN1368 datasheet(5/34 Pages) MICROCHIP

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 2011 Microchip Technology Inc.

DS01368A-page 5

AN1368

Some of the important properties of display

technologies are explained as follows:

• Frame Rate: The number of times the display

screen is refreshed in a second (this parameter

does not reflect the refresh capacity of the

microcontroller but only the capacity of the display

glass).

• Ghosting: When the screen is changed, the

previous frame is visible with lower intensity for a

fraction of time, which appears to be the ghost of

the current screen.

• HBLANK and VBLANK: Horizontal and vertical

blanking periods, where the display is not updated.

For more information, refer to Section 43. “Graph-

ics Controller Module (GFX)”

(DS39731) in the

“PIC24F Family Reference Manual”.

• Backlight: For TFT/STN LCDs, backlight is

necessary to view the display. It could be either

CCFL or LED type.

• Contrast: It is defined as the ratio of intensities of

white to black on the display. The higher the

contrast, the better is the display quality.

• Viewing Angle: It is the horizontal or vertical

angle within which the display is properly

viewable.

The display glass has no inherent memory and must be

constantly updated with pixel data in each row and

column, failing which, the display will go blank (similar

to DRAM refresh). This refreshing of the display data is

handled by the display controller.

Display Controller

The display glass must be constantly refreshed by

feeding the horizontal and vertical pixel data repeatedly

from the frame buffer. This task is performed by the

display controller. It fetches the data from the frame

buffer, decodes it to the required bit format and feeds it

to the display glass, along with proper control signals.

The display controller must adhere to the timing

requirements of the display glass.

Frame Buffer

The frame buffer is a memory (usually a RAM), which

holds the data to be shown on the display screen and

acts as the data source for the display controller. The

required size of the frame buffer depends on the

resolution and color depth. The minimum requirement

is that it should hold the data required to display one full

frame and must support the scan rate (preferred

refresh rate as per the data sheet of the display glass)

of the display controller.

EQUATION 1:

EXAMPLE 1:

EXAMPLE 2:

EXAMPLE 3:

Frame Buffer Size Required (Bytes) = Number of Pixels x

Color Depth (Bits)/8

For a QVGA (320x240) display using a 16 BPP color

depth:

Frame Buffer = 320 x 240 x 16/8

= 153,600 Bytes

= 150 Kbytes

For a WQVGA (480x272) display using a 16 BPP

color depth:

Frame Buffer = 480 x 272 x 16/8

= 261,120 Bytes

= 255 Kbytes

For a QCIF (176x144) display using an 8 BPP color

depth:

Frame Buffer = 176 x 144 x 8/8

= 25,344 Bytes

= 24.75 Kbytes

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