Datasheet

AN1368
DS01368A-page 12  2011 Microchip Technology Inc.
Display Orientation
Displays are available in Landscape (e.g., 320x240) or
Portrait (e.g., 240x320) modes. A landscape display
can also be used in Portrait mode by setting a 90°
rotate function in the graphics library or display
controller. Similarly, a portrait display can also be used
in Landscape mode. If rotating the pixels is
implemented by special hardware features inside the
graphics controller, there is no penalty on the
performance. However, if the rotation is performed in
software (such as the graphics library used), there is a
penalty in the software performance. This is because
for every (x, y) point, a new rotated (x’, y’) point has to
be calculated, which takes away some of the
processing power.
Note the difference in the RGB strip alignment if the
display is used in Rotated mode, as shown in
Figure 14.
Color Depth Selection
Along with the resolution of the display, the correct
choice of color depth is another decision factor since
this determines the size of the frame buffer (cost of
RAM). If natural photos are being displayed, it is better
to go with 16 BPP or higher. If 256 different colors are
enough for the application, then a color depth of 8 BPP
can be chosen (with the standard 256 colors provided
by the display controller or custom 256 colors using
CLUT (See Appendix A: “Color Look-up Table
(CLUT)”). This would reduce the RAM requirement by
50%, compared to 16 BPP. If only 16 or 4 different
colors are sufficient, 4 BPP or 2 BPP can be used,
saving the RAM by 75% and 87.5%, respectively, as
compared to 16 BPP. Tab le 3 lists the RAM
requirements for different color depths.
FIGURE 14: LANDSCAPE AND PORTRAIT DISPLAYS USED IN LANDSCAPE MODE
TABLE 3: RAM SIZE REQUIREMENT FOR DIFFERENT COLOR DEPTHS
BPP for QVGA (320x240) 16 BPP 8 BPP 4 BPP 2 BPP
Number of Colors 65,536 256 16 4
RAM Size (Bytes) 153,600 76,800 38,400 19,200