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PostPosted: Thu Aug 01, 2013 1:37 pm 
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Posts: 2286
In this thread, the OP said that Sony fixed the dot crawl issue by using a triangle wave color signal?

http://www.assemblergames.com/forums/sh ... eo-Encoder

Is this true, and does it really help get rid of dot crawl?


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PostPosted: Thu Aug 01, 2013 4:26 pm 
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Joined: Sun Apr 13, 2008 11:12 am
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Location: Seattle
psycopathicteen wrote:
Is this true, and does it really help get rid of dot crawl?
I don't really want to dig up my PS1 to connect to my oscilloscope ... but ok:
This is a SCPH-1001. It uses a CXA1645. The CD drive long since stopped working, and I removed the controller ports to build a card reader.
Scope was set to trigger on scanline #56, 'cuz it looked good enough. This is right at the start of the colorburst:
Attachment:
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IMG_0252.png [ 10.43 KiB | Viewed 1256 times ]
And this is later in the same scanline:
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IMG_0253.png
IMG_0253.png [ 9.51 KiB | Viewed 1256 times ]
Those sure looks sinusoidal to me. Or at least REALLY not triangular.

And no, nothing helps with dot crawl. Or more accurately, the only things that helps with dot crawl are
1- Never allowing chroma into your luma signal in the first place (s-video)
2- Never allowing chroma into your luma signal in the first place (the image having no sharp chroma edges anywhere)

You can see the dot crawl very clearly if you have a earlier-generation PS1 with the blue color theme BIOS (rather than the later grey themed one, which uses less outrageous colors and thus is less overwhelmingly obvious)


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PostPosted: Thu Aug 01, 2013 5:49 pm 
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Location: NE Indiana, USA (NTSC)
If I remember correctly, if you have a working disc drive, you can see dot crawl on the sides of the red P no matter what BIOS you use. Should I try it on a slim PS2 to see if it shows up there?

In any case a triangular carrier is probably several dB easier to filter down to a sinusoid than the NES's square carrier.


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