STV3550 datasheet(38/144 Pages) STMICROELECTRONICS

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STV3550

Graphics Functional Description

4.1.3.1 OSD Display Regions

The OSD consists of one or more display regions. Each display region is rectangular and can have

its own color palette and other properties. Three examples of OSD regions are shown in Figure 26.

In this figure, Region 3 shows that an OSD region can be displayed outside the active video area.

A single display line cannot be included in more than one active OSD region, i.e. only one OSD

region can be active on a single line. If two OSD regions are required to be displayed on the same

display line, a new OSD region must be defined that includes both regions.

For example, in Figure 27, two different OSD regions (A and B) use some of the same display lines.

If both OSD regions are to be active at the same time, a new region (C) must be defined including

both regions A and B. The area of region C that is outside regions A and B can be defined as

transparent.

4.1.4

Programming OSD Display Regions

The characteristics of each OSD region are contained in an OSD specification which is stored in the

64-Mbit SDRAM. The following data is contained in the OSD specification:

●

A header which defines the boundaries of the region and contains 4 pointers that are used to

identify the SDRAM location of the current palette, the current top block, the current bottom

block, the next OSD region and other control information.

Figure 26: OSD Regions

Figure 27: Two Display Regions using the same Display Lines

Boundary of displayable area

Active video area

(X0, Y0)

(X1, Y1)

Region 1

Region 2

Transparent

Region 3

Display lines

in both regions

OSD Regions

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