
LCD & VGA Controllers
11-5
GMS30C7201 Data Sheet
in use. (4 or 8 mono pixels per clock for mono panels, or 2
2
/
pixels per clock for color
data.) The output of the formatter in color mode is bursty, due to the 2
2
/
3
pixels per clock
that are output, so the formatter output goes to a small FIFO, which smooths out this
burstiness, before data is output to the LCD panel at a constant rate.
11.2.4 Color/Grayscale Dithering
Entries selected from the look-up palette are sent to the color/grayscale space/
timebase dither generator. Each 4-bit value is used to select one of 15 intensity levels.
Note that two of the 16 dither values are identical. The table below assumes that a pixel
data input to the LCD panel is active HIGH. That is, a
‘
1
’
in the pixel data stream will
turn the pixel on, and a
‘
0
’
will turn it off. If this is not the case, the intensity order will be
reversed, with
“
0000
”
being the most intense color. This polarity is LCD panel-
dependent.
The gray/color intensity is controlled by turning individual pixels on and off at varying
periodic rates. More intense grays/colors are produced by making the average time that
the pixel is off longer than the average time that it is on. The proprietary dither algorithm
is optimized to provide a range of intensity values that match the eye
’
s visual perception
of color/gray gradations, with smaller changes in intensity nearer to the mid-gray level,
and greater nearer the black and the white levels. In color mode, red, green and blue
components are gray-scaled simultaneously as if they were mono pixels.
The duty cycle and resultant intensity level for all 15 color/grayscale levels is
summarized in
Table 11-1: Color/grayscale intensities and modulation rates
.
Dither Value
(4-bit value from palette)
Intensity
(0% is white)
Modulation Rate
(ratio of ON to ON+OFF pixels)
0000
0.0%
0
0001
11.1%
1/9
0010
20.0%
1/5
0011
26.7%
4/15
0100
33.3%
3/9
0101
40.0%
2/5
0110
44.4%
4/9
0111
50.0%
1/2
1000
55.6%
5/9
1001
60.0%
3/5
1010
66.6%
6/9
1011
73.3%
11/15
1100
80.0%
4/5
1101
88.9%
8/9
1110
100.0%
1
1111
100.0%
1
Table 11-1: Color/grayscale intensities and modulation rates