sed1355 ETC-unknow, sed1355 Datasheet - Page 169

• Manufacturer Part Number: sed1355
• Description: Sed1355 Embedded Ramdac Lcd/crt Controller
• Manufacturer: ETC-unknow

Epson Research and Development
Vancouver Design Center
3.1.3 Memory Organization for Four Bit-Per-Pixel (16 Colors/Gray Shades)
3.1.4 Memory Organization for Eight Bit-Per-Pixel (256 Colors/16 Gray Shades)
Programming Notes and Examples
Issue Date: 99/04/27
Pixel 0
Bit 7
Bit 3
Bit 7
Figure 3-4: Pixel Storage for 8 Bpp (256 Colors/16 Gray Shades) in One Byte of Display Buffer
Pixel 0
Bit 6
Bit 2
Bit 6
Figure 3-3: Pixel Storage for 4 Bpp (16 Colors/Gray Shades) in One Byte of Display Buffer
In this memory format each byte of display buffer contains two adjacent pixels. Setting or resetting
any pixel will require reading the entire byte, masking out the upper or lower nibble (4 bits) and
setting the appropriate bits to ’1’.
Four bit pixels provide 16 gray shade/color possibilities. For monochrome panels the gray shades
are generated by indexing into the first 16 elements of the green component of the Look-Up Table.
For color panels the 16 colors are derived by indexing into the first 16 positions of the Look-Up
Table.
In eight bit-per-pixel mode each byte of display buffer represents one pixel on the display. At this
color depth the read-modify-write cycles of the lessor pixel depths are eliminated.
Each byte indexes into one of the 256 positions of the Look-Up Table. The SED1355 LUT supports
four bits per primary color, therefore this translates into 4096 possible colors when color mode is
selected. To display the fullest dynamic range of colors will require careful selection of the colors in
the LUT indices and in the image to be displayed.
When monochrome mode is selected, the green component of the LUT is used to determine the gray
shade intensity. The green indices, with only four bits, can resolve 16 gray shades. In this situation
one might as well use four bit-per-pixel mode and conserve display buffer.
Pixel 0
Bit 5
Bit 1
Bit 5
Pixel 0
Bit 4
Bit 0
Bit 4
One Pixel
Pixel 1
Bit 3
Bit 3
Bit 3
Pixel 1
Bit 2
Bit 2
Bit 2
Pixel 1
Bit 1
Bit 1
Bit 1
X23A-G-003-05
Pixel 1
Bit 0
Bit 0
Bit 0
SED1355
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