MB87P2020 Datasheet, PDF (174/356 Pages) Fujitsu Component Limited. – Colour LCD/CRT/TV Controller

MB87J2120, MB87P2020-A Hardware Manual
For the application within the GPU there are some simplifications: The basic equation is reduced to
y = m ⋅ x , with y representing the activity, x the modulation period and slope m the desired duty ratio. Fur-
ther, the distance ∆X can be limited to a power of 2. The value of the decision variable from Bresenham’s
algorithm distinguishing between y(k) and y(k) + 1 immediately tells when to set the signal active and
when inactive.
3.8.2 Usage
As listed in Table 2-2, there are two mappings for which the Duty Ratio Modulator is applied: from inter-
mediate 4bpp to physical 1bpp and for intermediate RGB222 to physical RGB111. Usage differs for either
case since a different number of pseudo levels is required.
Mapping from intermediate 4bpp to physical 1bpp
In this case there is a total of 16 different pixel values in intermediate color space which need be mapped to
a total of only two different pixel values in physical color space. The 16 intermediate values are interpreted
as gray scale, thus representing black, white and 14 levels of gray. These 14 levels have to be produced by
the DRM. The duty ratios used for this 14 pseudo levels are given in GPU registers (see chapter 4). Table
3-7 gives the assignment between pixel value and pseudo levels.
Table 3-7: Assignment between pixel values in intermediate and physical color space when using duty
ratio modulation for mapping from intermediate 4bpp to physical 1bpp.
pixel value
interm.
phys.
0 constant off
1 DRM 0 output
2 DRM 1 output
3 DRM 2 output
4 DRM 3 output
5 DRM 4 output
6 DRM 5 output
7 DRM 6 output
pixel value
interm.
phys.
8 DRM 7 output
9 DRM 8 output
10 DRM 9 output
11 DRM 10 output
12 DRM 11output
13 DRM 12 output
14 DRM 13 output
15 constant on
Please note that for a given DRM its output is either one or zero at any given time. What differs is the duty
ratio, which is adjustable via GPU register.
Mapping from intermediate RGB222 to physical RGB111
In this case the pixel value is interpreted as three color channels R, G, and B which are mapped individually
from intermediate to physical color space. Each intermediate color channel has a width of 2 bits, thus al-
lowing four different values. As a whole, intermediate RGB222 can represent 64 different colors.
However, since each color channel is regarded separately, there are only two pseudo levels per channel,
since the other two are constant on and off, respectively. Thus, a whole of six modulators is needed. Table
3-8 gives the assignment for this case.
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