ST92185B datasheet(92/178 Pages) STMICROELECTRONICS

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ST92185B - ON SCREEN DISPLAY (OSD)

ON SCREEN DISPLAY (Cont’d)

7.4.3.2 Color Processing

The color of any pixel on screen is the result of a

priority processing among several layers which

are (going from the lowest priority to the highest

one):

Full Screen Color where nothing is processed

Default Background Color (it assumes pixel is

off)

Serial

Background

Color

(pixel

off,

but

background color serial attributes activated)

Parallel

Background

Color

(pixel

off,

but

background color parallel attribute activated)

Default Foreground Color (pixel on, but no

foreground attribute activated)

Serial

Foreground

Color

(pixel

and

foreground serial attribute activated)

Parallel

Foreground

Color

(pixel

and

foreground parallel attribute activated)

Color processing is also the result of register con-

trol bits (for global color attributes) and color ori-

ented attribute bits (from serial or parallel at-

tributes), refer to the Figure 0.1.4.3

7.4.3.3 Pixel Clock Control

The pixel clock is generated outside of the display

macrocell by the on-chip Pixel Frequency multipli-

er which provides great frequency flexibility con-

trolled by software (refer to the RCCU chapter).

For example, reconfiguring the application from a

4/3 screen format to a 16/9 format is just a matter

of increasing the pixel frequency (i.e. reprogram-

ming the pixel frequency multiplier to its new val-

ue).

The output signal of the pixel frequency multiplier

is rephased by the Skew Corrector to be perfectly

in phase with the horizontal sync signal which

drives the display.

7.4.3.4 Display Character

Each character is made up of a 10 x 10 dots ma-

trix. All character matrix contents are fully user de-

finable and are stored in the pixel ROM (except the

G1 mosaic set which is hardware defined).

A set of colors defines the final color of the current

pixel.

In general, the character matrix content is dis-

played as it is, the pixel processing adding the

shape and the color information received from the

current attributes. Only three kinds of attributes al-

ter the displayed pixel. They are the following:

7.4.3.5 Rounding

Rounding can be enabled for the whole display us-

ing the GRE global attribute bit (See Figure 1) In

this effect one half-dot is added in order to smooth

the diagonal lines. This processing is built into the

hardware. The half-dot is painted as foreground.

This half-dot is field-sensitive for minimum vertical

size (Figure 4).

An extra ‘smooth rounding’ capability is also built-

in (see Figure 5). In smooth rounding, a pixel is

added even if dots make an ‘L’. This capability is

activated using a parallel attribute (See Table 4)

7.4.3.6 Underline

In this effect the last TV line of the character is dis-

played as foreground (Figure 4).

7.4.3.7 Fringe

The fringe is a half-dot black border surrounding

completely the character foreground. This half-dot

is field sensitive for minimum vertical size (Figure

4).

7.4.3.8 Translucency

Certain video processors are able to mix the RGB

and video signals. This function of the chroma pro-

cessor is then driven by the TSLU output pin of the

ST9 device. See Figure 7.

7.4.3.9 Half-Tone

If the HT signal is activated, for example, while a

text box is displayed and a transparant back-

ground selected for all the display (MM bit =1 in

the FSCCR register), the HT signal performs a

contrast reduction to the background inside the

box. See Figure 8.

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