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 Post subject: PAL Scanlines
PostPosted: Wed Dec 19, 2018 10:46 pm 
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Hey guys. Quick question regarding PAL scanlines. There are 312 scanlines per frame. 70 of them are VBlank, 1 is Post Render, 1 is Pre Render, and 239 of them are the actual visible screen. If you do the math, it only equates to 311 scanlines. 239 + 70 + 1 + 1 = 311. What is the missing scanline? Been scratching my head on this. Thanks in advance. :D


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 Post subject: Re: PAL Scanlines
PostPosted: Wed Dec 19, 2018 10:56 pm 
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What makes you think that there are only 239 visible scanlines?


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 Post subject: Re: PAL Scanlines
PostPosted: Wed Dec 19, 2018 10:58 pm 
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http://wiki.nesdev.com/w/index.php/Cycle_reference_chart

In here, it says that the height of the picture is 239 for PAL whereas NTSC is 240. That's where I got it from.


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 Post subject: Re: PAL Scanlines
PostPosted: Wed Dec 19, 2018 11:06 pm 
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Well, that cannot possibly be right, as you already found out yourself :)

I have never read anywhere that the PAL NES only shows 239 scanlines, see no reason why it would only show 239 while the NTSC NES shows 240, and remember seeing uncropped border tiles in SMB2/SMUSA's character selection screen.


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 Post subject: Re: PAL Scanlines
PostPosted: Wed Dec 19, 2018 11:14 pm 
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I don't have a PAL TV, but I've been told that the top, left and right lines of the 256x240 image are cut off on PAL. (Also, all borders are black, rather than colour 0.)

This video seems to demonstrate this with the SMB2 character select screen example: https://youtu.be/rAsc2NcdhyU?t=38s

I think you can consider this blank line as part of the normal "rendered" part of the screen though, just like you can consider the NTSC lines that aren't normally scene.


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 Post subject: Re: PAL Scanlines
PostPosted: Thu Dec 20, 2018 12:14 am 
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You can also see the left and right clipping in my (partial) PAL video capture. I never noticed that ... I am quite mystified why the 2C07 would do such a silly thing.

This however means that psychopathetica is correct and that the Cycle reference chart must be wrong by one scanline in this regard.


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 Post subject: Re: PAL Scanlines
PostPosted: Thu Dec 20, 2018 8:55 am 
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Yeah you are right. The left, right, and top lines are removed on PAL. The NTSC version only has the top removed as shown here:

https://youtu.be/tFPoNZoFBXM

Im thinking theres either one extra vblank, one extra dummy scanline, or maybe there is really only 311 scanlines. Im digging through other nes emulator source codes trying to find out but honestly I never seen this mentioned anywhere about this extra scanline.


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 Post subject: Re: PAL Scanlines
PostPosted: Thu Dec 20, 2018 9:02 am 
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But not even the top scanline should not be removed on NTSC. I think old VirtuaNES did it like that. I have no NTSC capture of SMB2 at the moment, but I do have one of Fire Emblem Gaiden:
Attachment:
FireEmblemGaiden.png
FireEmblemGaiden.png [ 166.44 KiB | Viewed 2253 times ]

The capture card had some problems syncing that very first scanline correctly (probably because the preceding scanline is one pixel too short), but it's there. The only known restriction regarding the first scanline is that you cannot show sprites there.


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 Post subject: Re: PAL Scanlines
PostPosted: Thu Dec 20, 2018 10:38 am 
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psychopathetica wrote:
Yeah you are right. The left, right, and top lines are removed on PAL. The NTSC version only has the top removed as shown here:
https://youtu.be/tFPoNZoFBXM

That 100% looks like an emulator to me. Try this instead: https://youtu.be/0UfDvWgJSnI?t=9s

The NES' NTSC signal has all 240 lines in it, but most TVs will cut off ~8 lines at the top and bottom (still true on modern HDTVs). I've seen many capture devices that can show a bit more than that.

The big telltale thing with NTSC is the horizontal blanks, which aren't very blank because they display colour 0.


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