6-24
Video Interface and On-Screen Display
Final Rev F
Copyright 1996 by LSI Logic Corporation. All rights reserved.
Table 6.10
Pull-Down
Mode Bits
6.9
On-Screen
Display
The L64005 integrates a exible on-screen display controller that allows
the overlay of text and graphics on top of the decoded video. The L64005
digitally mixes the overlay with the decoded video before outputting it on
the video port. The L64005 always displays the overlay data at the same
size regardless of the resolution or mode of the video data. Pan and scan
of the video data does not affect the position of the overlay data. The
L64005 supports two basic modes for the overlay data:
Up to 720 x 576 pixels at 2 bits/pixel
Up to 720 x 576 pixels at 4 bits/pixel
In addition, the L64005 can support various sub-formats, including 240-
line operation, which presents a full sized icker-free image.
6.9.1
Color Palette
The L64005 dynamically updates an on-chip color palette during the
overlay display process. The palette consists of 16 entries containing 6
bits of Y and 4 each of Cr,Cb. If Y = 4 (scaled 16), then Cr,Cb = 8 (scaled
128), and the output pixel is black. In the special case of Y = Cb = Cr =
0, the output pixel is transparent. This means that the overlay pixel is not
seen, and the pixel from the underlying decoded video is seen instead.
6.9.1.1 2 Bit/Pixel Mode
The L64005 reads overlay data from the DRAM frame stores and dis-
plays it at a rate of one pixel every two device clocks. Through an on-
chip color palette, the L64005 translates the 2-bit pixel value into a
YCbCr color value using 6 bits for Y, and 4 bits each for Cb and Cr. This
value allows 4 simultaneous colors to be selected from a palette of
approximately 16,384 non-black colors, plus black and transparent. The
Register 6:28,
Bit 4
Register 6:28,
Bit 3
Pull-Down Mode
0
No Pull-down
0
1
Constant: 3, 2, 3, 2
1
0
Pull-Down on each frame: 3, 3, 3, 3
1
Undened