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Intel® PXA255 Processor Developer’s Manual 7-11
LCD Controller
7.4.2 External Frame Buffer
The external frame buffer is an off-chip memory area used to supply enough encoded pixel values to fill
the entire screen one or more times. The number of pixel data values depends on the size of the
screen (for example, 640 x 480 = 307,200 encoded pixel values). Figure 7-6 through Figure 7-18
show the memory organization within the frame buffer for each size pixel encoding.
In the following figures, “Base” refers to the initial address programmed in the FSADR register,
“Palette Buffer Index” refers to the data that specifies the location in the palette buffer, and “Raw
Pixel Data” refers to the actual 16-bit RGB data when the palette RAM is bypassed.
Figure 7-6. 1 Bit Per Pixel Data Memory Organization
Figure 7-5. Palette Buffer Format
Individual Palette Entry
Bit1514131211109876543210
Color Red (R) Green (G) Blue (B)
Bit1514131211109876543210
Mono unused Monochrome (M)
Little Endian Palette Entry Ordering
4-, 16- or 256-Entry Palette Buffer
Bit 31 16 15 0
Base + 0x0 Palette entry 1 Palette entry 0
Base + 0x4 Palette entry 3 Palette entry 2
Entries 4 through 255 do not exist for 1 and 2
bits/pixel.
Base + 0x1C Palette entry 15 Palette entry 14
Base + 0x20 Palette entry 17 Palette entry 16
Entries 16 through 255 do not exist for
1, 2, and 4 bits/pixel.
Base +
0x1FC
Palette entry 255 Palette entry 254
Bit 0
1 bit/pixel Palette Buffer Index[0]
Bit31302928... 3 2 1 0
Base +
0x0
Pixel 31 Pixel 30 Pixel 29 Pixel 28 ... Pixel 3 Pixel 2 Pixel 1 Pixel 0
Base +
0x4
Pixel 63 Pixel 62 Pixel 61 Pixel 60 ... Pixel 35 Pixel 34 Pixel 33 Pixel 32