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Functional Description (Continued)

3.8.3

Video Overlay

The video data from the color-space converter is then

mixed with the graphics data based upon the video window

position. The video window position is programmable via

the Video X and Y Position Registers (F4BAR+Memory

Offset 08h and 0Ch). A color-keying mechanism is

employed to compare either the source (video) or destina-

tion (graphics) color to the color key programmed via the

Video Color Key Register (FBAR+Offset 14h) and to select

the appropriate pixel for display within the video window.

The range of the color key is programmable by setting the

appropriate bits in the Video Color Mask Register

(F4BAR+Memory Offset 18h). This mechanism greatly

reduces the software overhead for computing visible pixels,

and ensures that the video display window may be partially

occluded by overlapping graphics data. Tables 3-74 and 3-

75 show the bit formats for these registers

The CS5530A accepts graphics data over the PIXEL[23:0]

interface from the GX-series processor at the screen DOT

clock rate. The CS5530A is capable of displaying graphics

resolutions up to 1600x1200 at color depths up to 24 bits

per pixel (bpp) while simultaneously overlaying a video win-

dow. However, system maximum resolution is not deter-

mined by the CS5530A since it is not the source of the

graphics data and timings.

Table 3-74. Video X and Y Position Registers

Bit

Description

F4BAR+Memory Offset 08h-0Bh

Video X Register (R/W)

Reset Value = xxxxxxxxh

31:27

Reserved: Set to 0.

26:16

VideoXEndPosition: This field represents the horizontal end position of the video window according to the following

formula. Position programmed = screen position + (H_TOTAL – H_SYNC_END) – 13.

15:11

Reserved: Set to 0.

10:0

Video X Start Position: This field represents the horizontal start position of the video window according to the following

formula. Position programmed = screen position + (H_TOTAL – H_SYNC_END) – 13.

F4BAR+Memory Offset 0Ch-0Fh

Video Y Register (R/W)

Reset Value = xxxxxxxxh

31:27

Reserved: Set to 0.

26:16

VideoY EndPosition: This field represents the vertical end position of the video window according to the following formula.

Position programmed = screen position + (V_TOTAL – V_SYNC_END) + 1.

15:11

Reserved: Set to 0.

10:0

Video Y Start Position: This field represents the vertical start position of the video window according to the following

formula. Position programmed = screen position + (V_TOTAL – V_SYNC_END) + 1.

Table 3-75. Video Color Registers

Bit

Description

F4BAR+Memory Offset 14h-17h

Video Color Key Register (R/W)

Reset Value = xxxxxxxxh

31:24

Reserved: Set to 0.

23:0

Video Color Key: This field represents the video color key. It is a 24-bit RGB value. The graphics or video data being

compared may be masked prior to the compare by programming the Video Color Mask Register (F4BAR+Memory Offset

18h) appropriately.

F4BAR+Memory Offset 18h-1Bh

Video Color Mask Register (R/W)

Reset Value = xxxxxxxxh

31:24

Reserved: Set to 0.

23:0

Video Color Mask: This field represents the video color mask. It is a 24-bit RGB value. Zeroes in the mask cause the

corresponding bits in the graphics or video stream being compared to be ignored.

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