
3 MEMORY MODELS
SID13705 PROGRAMMING NOTES
EPSON
C-2-5
AND EXAMPLES
3
MEMORY MODELS
The SID13705 block is capable of operating at four different color depths. For each color depth
the data format is packed pixel. SID13705 block packed pixel modes can range from one byte
containing eight adjacent pixels (1-bpp) to one byte containing just one pixel (8-bpp).
Packed pixel data may be envisioned as a stream of pixels. In this stream, pixels are packed in
adjacent to each other. If a pixel requires four bits then it will be located in the four most
significant bits of a byte. The pixel to the immediate right on the display will occupy the lower
four bits of the same byte. The next two pixels to the immediate right are located in the following
byte, etc.
3.1 1 Bit-Per-Pixel (2 Colors/Gray Shades)
1-bit pixels support two color/gray shades. In this memory format each byte of display buffer
contains eight adjacent pixels. Setting or resetting any pixel requires reading the entire byte,
masking out appropriate bits and, if necessary, setting bits to “1”.
When using a color panel the two colors are derived by indexing into positions 0 and 1 of the
Look-Up Table. If the first two LUT elements are set to black (RGB = 0 0 0) and white (RGB = F
F F) then each “0” bit of display memory will display as a black pixel and each “1” bit will display
as a white pixel. The two LUT entries can be set to any desired colors, for instance red and green
or cyan and yellow.
For monochrome panels the two displayed gray shades are generated by indexing into the first two
elements of the green component of the Look-Up Table (LUT). Thus, by manipulating the green
LUT components we can set either of the two gray shades to any of sixteen possible levels.
Figure 3-1 Pixel Storage for 1 Bpp (2 Colors/Gray Shades) in One Byte of Display Buffer
3.2 2 Bit-Per-Pixel (4 Colors/Gray Shades)
2-bit pixels support four color/gray shades. In this memory format each byte of display buffer
contains four adjacent pixels. Setting or resetting any pixel requires reading the entire byte,
masking out the appropriate bits and, if necessary, setting bits to “1”.
Color panels derive their four colors by indexing into positions 0 through 3 of the Look-Up Table.
These four LUT entries can be set to any of the 4096 possible color combinations.
Monochrome panels derive four gray shades by indexing into the first four elements of the green
component of the Look-Up Table. Any of the four LUT entries can be set to any of the sixteen
possible gray shades.
Figure 3-2 Pixel Storage for 2 Bpp (4 Colors/Gray Shades) in One Byte of Display Buffer
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Pixel 0
Pixel 1
Pixel 2
Pixel 3
Pixel 4
Pixel 5
Pixel 6
Pixel 7
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Pixel 0
Bit 1
Pixel 0
Bit 0
Pixel 1
Bit 1
Pixel 1
Bit 0
Pixel 2
Bit 1
Pixel 2
Bit 0
Pixel 3
Bit 1
Pixel 3
Bit 0