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  • Writer's pictureMike Chi

Where's the COMP2RGB?

I thought I'd give an update on the COMP2RGB project, the component to RGB transcoder. When I started this project, I thought it was going to be a breeze: follow the LMH1251 datasheet to the dot, add a sync stripper, output buffer and we're good to go right?

Aside from flipping the CVBS and audio pins on the SCART (SHART) connector, the production samples appeared to work beautifully. The LHM1251 even took care of removing the sync signals from the output lines. This is great, because I was about to implement a discrete one from some TI high speed, limiting opamp.

Unfortunately, as with many engineering projects, simple things are never as straightforward as they look and black-boxes often have undesirable behavior that is difficult to assess and correct.

Thanks to Dave Kircher (, we discovered an issue with the LM1251 where rapid resolution switches from 1080i back to SDTV resolution cause the LMH1251 sync processing and stripping circuits to enter a weird state. This wouldn't be a problem for normal consumer video applications, but it appears that at least on the PS2 (GT4), the resolution switches fast enough to trick the chip.

Long story short, now implementing a supervisor circuit to manually power cycle the LMH1251 upon switches between HDTV and SDTV signals. Fingers crossed and stay tuned!

In the meantime, enjoy the RGB2COMP :)


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