AL250 International Power Sources, Inc., AL250 Datasheet - Page 15

• Manufacturer Part Number: AL250
• Description: Video Scan Doubler
• Manufacturer: International Power Sources, Inc.

Similar to bitmap 1, each pixel is defined by 2 bits value (“00”, “01”, “10” and “11”) with the same
definition.
The horizontal positions of the bitmaps 1 & 2 are defined by registers 1Eh and 1Fh respectively. The
vertical position of both is defined by register 2Fh.
For the external OSD, the overlay feature needs to be used and this will be explained in detail in the
External Overlay section.
OSD control applies to the AL250/251 analog output and the AL251 digital RGB output, but not to
the AL251 digital YUV output.
6.6 External Overlay
The AL250/251 provides two overlay pins (OVLCTRL1 and OVLCTRL0) for overlay control as well
as some special effects. They can be pulled as 00 for no overlay, and 01, 10, 11 for different overlay
colors or effects. The colors can be chosen from any one of 16M colors (defined by 24 bits RGB) by
programming registers 15h~1Dh. The effects can be logic AND, OR, or XOR of the video source
with any of the three overlay colors by programming register 14h. For instance, a negative film effect
can be produced by XOR the original video source with white color. More details can be found in the
Register Definition section.
Using the external overlay of the AL250/251 for caption display is possible if the OSD or FPGA chip
chosen for displaying fonts of the decoded caption has the two overlay pins compatible with the
AL250. If not, then the digital or analog output of the OSD can still be multiplexed with the output
of the AL250/251 to show captions on the video display.
1<7:0>
2<7:0>
3<7:0>
7:6
5:4
3:2
1:0
0<7:0>
4<7:0>
5<7:0>
AL250-17 16x48 OSD drawing
July 28, 1999
AL250
188<7:0>
189<7:0>
190<7:0>
191<7:0>
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