Decoding the Gameboy LCD output.

stevestrong
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Re: Decoding the Gameboy LCD output.

Post by stevestrong » Tue Nov 14, 2017 10:21 am

My problem here is that I don't have a clear scope plot to see the correct timings.
I tried to google it, and I have found this: (from here: http://www.mindspring.com/~mickeym/gameboy.htm)

Image

Applies this in your case, too?
If yes, then you have indeed 20µs time till the first clk pulse.
But the clock seems very weird to me, it is low, then goes to high and then starts to toggle, but not continuously?
Can you eventually take a cleaner plot?

ZeroWalker
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Re: Decoding the Gameboy LCD output.

Post by ZeroWalker » Tue Nov 14, 2017 3:53 pm

Well tbh i find the Clock Pulse really weird as well.

First it's Off, then it goes on/off, then it waits for awhile, then it goes in a decent interval.

It seems to be 1 first pulse, them a "timeout" then 159 pulses afterwards.
For me the first pixel is messed up, but i am not sure if this is why (i am decoding it wrong) or if it's my gameboy as it's HSYNC is broken so i can't see the original screen.

I can give you my Salae file with all the data, except HSYNC, you need the Logic software to look at it,
but it's very good as you can zoom in and out and measure etc, not sure where to upload it though, it's about 3mb compressed.

dave j
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Re: Decoding the Gameboy LCD output.

Post by dave j » Tue Nov 14, 2017 5:43 pm

There's an article Sniff your Game Boy's LCD using a logic analyzer where someone describes capturing GameBoy screen output using a Saleae logic analyzer. It might help you make sure you're capturing things correctly.

ZeroWalker
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Re: Decoding the Gameboy LCD output.

Post by ZeroWalker » Tue Nov 14, 2017 6:37 pm

Yeah that's what i used as a source for this.

stevestrong
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Re: Decoding the Gameboy LCD output.

Post by stevestrong » Tue Nov 14, 2017 6:51 pm

But those signals are different from those I pasted.
Here the Vsync is one short pulse, on my picure the Vsync is along pulse.
Also, the clock signal in my pic is only generated for the active lines, here is continuous.

ZeroWalker
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Re: Decoding the Gameboy LCD output.

Post by ZeroWalker » Tue Nov 14, 2017 6:55 pm

not sure which pictures you are comparing with, those i see look similar to mine.

EDIT:

Even when using Salae though i get a corrupt first pixel column.
2017-11-14_20-00-51.png
2017-11-14_20-00-51.png (9.52 KiB) Viewed 49 times
EDIT2:

Here's a similar screenshot to the one from the git project.
2017-11-14_20-04-11.png
2017-11-14_20-04-11.png (38.23 KiB) Viewed 49 times
EDIT3:

Might be game dependent as this looks fine.
2017-11-14_20-11-25.png
2017-11-14_20-11-25.png (7.85 KiB) Viewed 49 times
Last edited by ZeroWalker on Tue Nov 14, 2017 7:20 pm, edited 2 times in total.

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RogerClark
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Re: Decoding the Gameboy LCD output.

Post by RogerClark » Tue Nov 14, 2017 7:16 pm

@zerowalker

Images in your last post dont display

ZeroWalker
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Re: Decoding the Gameboy LCD output.

Post by ZeroWalker » Tue Nov 14, 2017 7:18 pm

They don't?

They show fine for me O.o?

Is this site blocked or something for you guys: http://abload.de/

EDIT:

Replaced them using attachments now.

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RogerClark
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Re: Decoding the Gameboy LCD output.

Post by RogerClark » Tue Nov 14, 2017 7:29 pm

Thanks

Perhaps that site is blocked by the Australian government.. more and more of the internet is getting blocked for me

ZeroWalker
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Re: Decoding the Gameboy LCD output.

Post by ZeroWalker » Tue Nov 14, 2017 7:42 pm

Oh, that's scary :(

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