CS9211 datasheet(26/62 Pages) NSC

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Revision 2.1

Functional Description (Continued)

3.2.4

Frame Rate Modulation

The Frame Rate Modulation (FRM) scheme is the heart of

the CS9211. Frame Rate Modulation cannot be turned off

but it can be modified through certain programming regis-

ters and internal memories.

Each pixel on an LCD panel consists of three primary color

components: red, green, and blue. Each primary color

component, for a given pixel, can either be turned on or

turned off; there are no intermediate intensities. A total of

eight colors can be generated for a given pixel through var-

ious combinations of turning each color component on or

off. In order to generate more colors, Frame Rate Modula-

tion (and dithering) is used. The idea behind Frame Rate

Modulation is to turn each primary color component of a

pixel on and off a certain fraction of the time to create the

perception of intensities between fully off and fully on.

For example, imagine a pixel whose blue and green color

components are always off. If the pixel’s red color compo-

nent was also always off, the pixel would be black. If the

pixel’s red color component was always on, the pixel would

be the brightest red. If the red color component was blink-

ing on and off for equal intervals, then the pixel would look

about half as bright as the brightest red. Use of intervals

other than 50%-on/50%-off will yield other intensities

between black and fully bright. Assuming the blink rate is

sufficiently fast, a viewer’s eye would integrate the intensity

of a modulated pixel to perceive intensities between fully off

(black) and fully on (bright red).

The FRM algorithm in the CS9211 uses 64-frame-long

sequences to determine when to turn the red, green, and

blue pixel color components on and off. (A frame is one

complete image on a panel.) The sequence repeats itself

every 64 frames. The CS9211 contains one 64-bit x 32-bit

FRM memory for each of the three primary pixel colors,

red, green, and blue. These three memories can be pro-

grammed simultaneously or individually. Each of the three

memories holds up to 32 different modulation sequences,

therefore 32 different intensities for each primary color

component can be generated by Frame Rate Modulation.

The memory values can be set to provide any intensity

variation to accommodate the properties of different LCD

panels, but for best results, successive values should

increase monotonically.

The number of discrete intensities is chosen with Offset

40Ch[6:4] (see Table 3-9). These bits determine how many

of the most significant bits of each pixel value for each color

component will be used by the FRM algorithm to generate

the base intensities. FRM can use 5-bit to 1-bit schemes in

order to share the 6-bit input. If a 5-bit FRM scheme is

used, there are 25 (32) base intensities (prior to dithering).

If a 1-bit scheme is used, only 21 (2) intensities are avail-

able, with the first 16 intensities having one bit sequence

and the next 16 intensities using the other bit sequence.

Table 3-9. Frame Rate Modulation Control Bit

Bit

Name

Description

Offset 40Ch-40Fh

Dither and Frame Rate Control Register (R/W)

Reset Value = 00000000h

6:4

NO_OF_FRM

INTENSITIES

Number Of FRM Intensities: The value set by bits [6:4] is the number of intensities that will exist due to

Frame Rate Modulation, prior to dithering. This field selects how many of the incoming most significant

data bits (per color) are used to generate the FRM intensities.

000 = 2 FRM intensities (selects 1 MS (most-significant) bit for use by FRM).

001 = 4 FRM intensities (selects 2 MS bits for use by FRM).

010 = 8 FRM intensities (selects 3 MS bits for use by FRM).

011 = 16 FRM intensities (selects 4 MS bits for use by FRM).

100 = 32 FRM intensities (selects 5 MS bits for use by FRM).

101, 110, 111 = Reserved.

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