MCD212 Motorola, MCD212 Datasheet - Page 54

• Manufacturer Part Number: MCD212
• Description: Video Decoder and System Controller(with JTAG)
• Manufacturer: Motorola

To decode the pixel streams entering via channel 1 and channel 2, several decoders are available: one
delta YUV decoder per channel, one color look up table (CLUT) to be shared by both channels, and
direct RGB to be generated via both channels. The decoded pixel streams represent the two graphics
planes: A and B. The cursor and backdrop are programmed via channel 1.
7.1
YUV stands for luminance (Y) and color difference (U and V). The U and V components are horizon-
tally subsampled by a factor of two and transmitted alternatively every other pixel. The missing U and
V components are interpolated using linear interpolation. The human eye is much less sensitive to
color variation than variations in luminance, therefore any error due to interpolation will not be de-
tected. The last missing U or V component of a line is found by repeating the last U or V component.
The Y component ranges from 0 to 255. The U and V components are signed but are given an offset
of 128 to make them positive. The U and V components then range from 1 to 255. The expected
ranges for R, G, and B are from 0 to 255. To avoid wrap–around for values outside this range, output
limiters are implemented.
The absolute Y, U, and V components are decoded to R, G, and B using the following equations:
Delta YUV (DYUV) coding is particularly useful for the reproduction of high quality natural images.
These images typically have a high degree of correlation between adjacent pixels. This correlation is
used in delta YUV decoding by only coding the difference between adjacent pixels rather than their
absolute value; this is the delta. This difference is coded in 4 bits, using a non–uniform 16–level fixed
quantizer. The VDSC executes the opposite operation, using the values in Table 7–1.
MOTOROLA
R = lim[ trunc{ ( Y*256 + 351*(V – 128) ) / 256 } ]
G = lim[ trunc{ ( Y*256)(86*(U – 128) + 179*(V – 128)) ) / 256 } ]
B = lim[ trunc{ ( Y*256 + 444*(U – 128) ) / 256 } ]
trunc{x} = greatest integer less than or equal to x
lim[x] = 0 if x < 0
= 255 if x > 255
= x else
DELTA YUV DECODER
MCD212
REAL-TIME DECODER
7
7–1