MCD212 Datasheet, PDF (51/87 Pages) Motorola, Inc – Video Decoder and System Controller(with JTAG)

MEMORY DATA BUS MD15 – MD0
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
1ST BYTE
2ND BYTE
7 6 5 4 3 2 10 7 6 5 4 3 2 1 0
PIXEL 1
PIXEL 2
Figure 6–1. Bitmap Serialization in 8 Bits/Pixel
MEMORY DATA BUS MD15 – MD0
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
1ST NIBBLE 2ND NIBBLE 3RD NIBBLE 4TH NIBBLE
BIT BIT
32 1 0
PIXEL 1
BIT BIT BIT BIT
32 1 0 32 1 0
PIXEL 2
PIXEL 3
BIT BIT
32 1 0
PIXEL 4
Figure 6–2. Bitmap Serialization in 4 Bits/Pixel
6.2
RUN-LENGTH FILE
The run–length coding technique permits file compression by grouping into one block consecutive
pixels that have the same color. The VDSC uses either a 7– or a 3–bit color look up table (CLUT) to
provide either 1 out of 128 colors or 1 out of 8 different colors. The run–length compression is applied
to each video line independently of the others. The run–length file is organized as a list of information
about pixels without any notion of width or height as in bitmap files. (Refer to Section 7.2, CLUT De-
coder.)
6.2.1 Run-length 7-Bit CLUT Files
Run–length 7–bit CLUT files are either a single byte (for a single pixel) or two bytes (for a run of pixels
on a single line) in length. A 0 in the first bit indicates a single pixel CLUT address whereas a 1 in the
first bit indicates a run of pixels on the present line. The run only extends to the end of the line and
does not continue to the next line. The second byte indicates the number of identical pixels to be
reproduced on the current line. A 0 in the second byte indicates that this color is to be repeated to the
end of the line. A 1 is forbidden in the second byte. The eight bits allowed for 2 to 255 identical bits
to be repeated or with a 0, the rest of the line will have the same pixel repeated. Every line must finish
with a “zero–length” run (N = 0), which means that at a minimum, the last two pixels of the line are
identical. Figure 6–3 shows the format for both.
SINGLE
PIXEL
0 7–BIT CLUT ADDRESS
7
6
0
MULTIPLE
PIXELS
1
7–BIT CLUT ADDRESS
N = NUMBER OF IDENTICAL PIXELS (8 BITS)
15
14
87
0
NOTE: N = 0 means “duplicate this pixel to the end of the line”.
N = 1 is forbidden.
Figure 6–3. Run–length Format in 7 Bits/Pixel
6–2
MCD212
MOTOROLA