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 Post subject: Re: SNES Digital RGB Output TST Pins
PostPosted: Wed Jul 01, 2020 6:39 pm 


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Opatus wrote:
The PPU2 has to do the window effects so I assume it should know everything about the sprites and the backgrounds. It also does mosaic (according to the manual) and it is only performed on the backgrounds.

Maybe mosaic is split between the PPUs? PPU2 is not connected to the video address bus, so PPU1 always determines what data is fetched, but PPU2 could decide to throw some of it away and just repeat the previous value to create the horizontal aspect of the mosaic effect.
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 Post subject: Re: SNES Digital RGB Output TST Pins
PostPosted: Thu Jul 02, 2020 12:23 pm 


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Yes, you are right, then it must be split betweeen the two and the manual is incorrect or half correct.


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 Post subject: Re: SNES Digital RGB Output TST Pins
PostPosted: Fri Jul 03, 2020 8:51 am 


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After shorting a few pins with a pair of tweezers (very professional) I can confirm that the CHAR, COLOR and PRIO pins are used for the sprites, at least in Mode 7. And as expected the graphics data comes from the U4 SRAM chip.
So if the timing of the OVER signal is correct, this solution should work.


Last edited by Opatus on Sun Jul 05, 2020 10:28 pm, edited 1 time in total.

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 Post subject: Re: SNES Digital RGB Output TST Pins
PostPosted: Sat Jul 04, 2020 4:32 pm 



Joined: 27 Sep 2019
Posts: 37
The PVM screenshot looks good! I'm sure any improvement from here is negligible for analog applications. I have a board on the way for a basic DAC. No circuitry for brightness control yet. I'm not smart enough to investigate anything beyond this point, but I'll post results of my DAC when it comes (assuming it works!).


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 Post subject: Re: SNES Digital RGB Output TST Pins
PostPosted: Sun Jul 05, 2020 11:03 pm 


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I've made a little test to prove the concept by lifting the LSB of the data line and connecting it to the CPLD. In Mode 7 transparent mode the line is pulled high when the OVER signal is low, otherwise the original data is passed through. On the image below it can be seen that it works, the timing of the OVER signal is perfect for our purpose (which is not a big surprise) and the sprites remained intact.
Image

I've also changed the timing of the digital output deactivation: turned off during vsync and forced blanking. This seems to have solved the issues with Donkey Kong without the palette color problems.

Next step is a new board with all the improvements.

@yoshiyukiblade
Please keep us updated with your progress.


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 Post subject: Re: SNES Digital RGB Output TST Pins
PostPosted: Mon Jul 13, 2020 8:34 pm 


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I add an image for clarity, (this was taken after I changed the fuse in my SNES and repaired my improvised programmer). Now the data bit0 for the PPU2 is negated and every pixel which should be transparent has its color changed. The sprites and the non-transparent background remain unchanged.

Image


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 Post subject: Re: SNES Digital RGB Output TST Pins
PostPosted: Sat Aug 15, 2020 9:05 pm 



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@Opatus

This is incredible work. I know that byuu was calling for work like this as a way to figure out accurate cycle times for the PPU https://arstechnica.com/gaming/2020/04/ ... erfection/ Last I heard they contracted someone to do 100x die scans of the PPUs but your mod may accelerate their work, thought I am not sure if there is a specific torch bearer on that project anymore since byuu has retired.

Is there a possibility for an HDMI mod? I know that the NTSC/HDMI timings aren't compatible but maybe you could make something that has 1-frame buffer delay? Not sure.

I cannot tell for certain but it seems that it's possible to get a pixel perfect picture once all the relevant signals are analyzed and accounted for. What do you think? Do you need an SD2SNES cart? A spare SNES/SFC/PAL SNES? I can possibly help provide you with those tools.


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 Post subject: Re: SNES Digital RGB Output TST Pins
PostPosted: Tue Aug 18, 2020 10:02 pm 


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I've read that article a few months ago and then I was surprised nobody looked into it further if it was that well known. I did not know that byuu retired, I've read his farewell now, it's really sad.

The HDMI mod will happen eventually just not by me, provided everything works as intended.

I did not know why would have byuu need a perfectly working digital mod to analyze the signals. The parts that were not working could have been ignored as these had basically nothing of value (almost) for emulation.

Thank you for your offerings but I think I don't need them. The PPU chips are identical for every regions and I have 20-30 carts, it should be sufficient to decide if everything is working or not. Also I'm not analyzing the signals in depth, I am just using them for the video modification and optimizing the timing if needed.


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 Post subject: Re: SNES Digital RGB Output TST Pins
PostPosted: Wed Sep 30, 2020 7:40 pm 


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Just a quick update. The new board is ready and new results can be expected in 2-3 weeks.

Image


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 Post subject: Re: Sharp video output for the 3-Chip SNES using digital sig
PostPosted: Fri Oct 02, 2020 12:10 am 



Joined: 27 Sep 2019
Posts: 37
Looks exciting! Hoping for positive results.


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 Post subject: Re: Sharp video output for the 3-Chip SNES using digital sig
PostPosted: Fri Oct 02, 2020 10:05 pm 


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What's the difference between the 3-Chip and 2-Chip? I have heard people saying they don't want to get anywhere near the 1-Chip version because it's "not the original" or whatever, but then seems like there isn't two types of SNES consoles, but 3 types "3-Chip", "2-Chip" and "1-Chip", so then that means 2 two of these are "not the original" and only one is, so which is the original SNES design, 3-Chip or 2-Chip?


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 Post subject: Re: Sharp video output for the 3-Chip SNES using digital sig
PostPosted: Sat Oct 03, 2020 12:07 am 


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Lawfer wrote:
What's the difference between the 3-Chip and 2-Chip?

Different ways of counting the chips on the same board. 3-Chip counts all "major" chips (CPU, PPU1, PPU2), 2-Chip only counts the PPUs.

Quote:
so which is the original SNES design, 3-Chip or 2-Chip?

Both and neither. =) The original SNES design had the sound subsystem on a separate module and the CPU+PPU1+PPU2 on the main PCB. The sound stuff was integrated into the main PCB in later revisions which still had the same CPU+PPU1+PPU chips, so these boards are still called 2/3-chip SNESs. The actual change that does make a difference is the one to the 1-Chip version which combines the CPU and both PPUs into a single chip, but the sound subsystem is still separate.
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 Post subject: Re: Sharp video output for the 3-Chip SNES using digital sig
PostPosted: Sat Oct 03, 2020 1:46 pm 


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Unseen wrote:
Different ways of counting the chips on the same board. 3-Chip counts all "major" chips (CPU, PPU1, PPU2), 2-Chip only counts the PPUs.

Both and neither. =) The original SNES design had the sound subsystem on a separate module and the CPU+PPU1+PPU2 on the main PCB. The sound stuff was integrated into the main PCB in later revisions which still had the same CPU+PPU1+PPU chips, so these boards are still called 2/3-chip SNESs. The actual change that does make a difference is the one to the 1-Chip version which combines the CPU and both PPUs into a single chip, but the sound subsystem is still separate.


So wait, if I understand correctly you are saying that 3-Chip and 2-Chip SNES are just different names for the same exact model? Is that it?


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 Post subject: Re: Sharp video output for the 3-Chip SNES using digital sig
PostPosted: Sat Oct 03, 2020 2:10 pm 


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Lawfer wrote:
Unseen wrote:
Different ways of counting the chips on the same board. 3-Chip counts all "major" chips (CPU, PPU1, PPU2), 2-Chip only counts the PPUs.

Both and neither. =) The original SNES design had the sound subsystem on a separate module and the CPU+PPU1+PPU2 on the main PCB. The sound stuff was integrated into the main PCB in later revisions which still had the same CPU+PPU1+PPU chips, so these boards are still called 2/3-chip SNESs. The actual change that does make a difference is the one to the 1-Chip version which combines the CPU and both PPUs into a single chip, but the sound subsystem is still separate.


So wait, if I understand correctly you are saying that 3-Chip and 2-Chip SNES are just different names for the same exact model? Is that it?

3 chip and 2 chip refer to the same group of models


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 Post subject: Re: Sharp video output for the 3-Chip SNES using digital sig
PostPosted: Sat Oct 03, 2020 2:35 pm 


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maxtherabbit wrote:
Lawfer wrote:
Unseen wrote:
Different ways of counting the chips on the same board. 3-Chip counts all "major" chips (CPU, PPU1, PPU2), 2-Chip only counts the PPUs.

Both and neither. =) The original SNES design had the sound subsystem on a separate module and the CPU+PPU1+PPU2 on the main PCB. The sound stuff was integrated into the main PCB in later revisions which still had the same CPU+PPU1+PPU chips, so these boards are still called 2/3-chip SNESs. The actual change that does make a difference is the one to the 1-Chip version which combines the CPU and both PPUs into a single chip, but the sound subsystem is still separate.


So wait, if I understand correctly you are saying that 3-Chip and 2-Chip SNES are just different names for the same exact model? Is that it?

3 chip and 2 chip refer to the same group of models


But they're different, right?


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 Post subject: Re: Sharp video output for the 3-Chip SNES using digital sig
PostPosted: Sat Oct 03, 2020 2:37 pm 


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Lawfer wrote:
But they're different, right?

no, there is no such thing as a 2 chip

every SNES before the 1 chip is a 3 chip, but they are not all the same model

2 chip is a malapropism


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 Post subject: Re: Sharp video output for the 3-Chip SNES using digital sig
PostPosted: Sat Oct 03, 2020 2:42 pm 



Joined: 07 Jul 2020
Posts: 47
That sharp photo of Zelda there - drool worthy to get that out of original hardware ! I’d say *sold* if it weren’t for the PPU needing to be removed and replanted... that seems a bit excruciating unless you have the infrared bench


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 Post subject: Re: Sharp video output for the 3-Chip SNES using digital sig
PostPosted: Sat Oct 03, 2020 2:50 pm 



Joined: 03 Jul 2020
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VajSkids Consoles wrote:
That sharp photo of Zelda there - drool worthy to get that out of original hardware ! I’d say *sold* if it weren’t for the PPU needing to be removed and replanted... that seems a bit excruciating unless you have the infrared bench


You could probably take it off pretty easily with some low melting point solder or hot air.


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 Post subject: Re: Sharp video output for the 3-Chip SNES using digital sig
PostPosted: Sat Oct 03, 2020 8:06 pm 



Joined: 07 Jul 2020
Posts: 47
Yeah but then it needs a transplant. You’ve already seen how his originally transplanted one came out (this isn’t having a crack at you, that shits super difficult)

But if you use one of those Benches used for reballing GPU’s etc it would be a sinch, got a cheap one off eBay years ago and it worked a treat. It does bursts of infrared rather than constant heat and the advantage is it seems to get the solder flowing without heating up the IC too much.

To reseat it you just put some solder on the new boards footprint. Not a tonne just enough. Take some time getting it perfectly into place and then infrared it back on.


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 Post subject: Re: Sharp video output for the 3-Chip SNES using digital sig
PostPosted: Sat Oct 03, 2020 9:15 pm 


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Removing the PPU is easy with hot air if you are careful. Soldering it on is even easier with a simple iron.

The damage did not happen during the removal of it. Before I've removed it I was probing the TST pins a lot and after some time a few pins have broken off. I was a bit careless because I was under the impression that the PPU2 was faulty (missing sprites), but most likely I was wrong.


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 Post subject: Re: Sharp video output for the 3-Chip SNES using digital sig
PostPosted: Sun Oct 04, 2020 4:50 am 



Joined: 07 Jul 2020
Posts: 47
Opatus wrote:
Removing the PPU is easy with hot air if you are careful. Soldering it on is even easier with a simple iron.

The damage did not happen during the removal of it. Before I've removed it I was probing the TST pins a lot and after some time a few pins have broken off. I was a bit careless because I was under the impression that the PPU2 was faulty (missing sprites), but most likely I was wrong.


No worries- been a while since I opened a SNES/ Famicom. I actually chose to use my super famicom over my one chip because it was a little bright of an output and I couldn’t be bothered opening it up to add the 3 x 75ohm resistors known as a fix.

Anyway, I’d never attempt to using an iron on say, a megadrive VDP transplant. Those pins are insanely close and brittle


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 Post subject: Re: Sharp video output for the 3-Chip SNES using digital sig
PostPosted: Mon Oct 05, 2020 6:19 pm 



Joined: 30 Sep 2020
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This is awesome, Opatus! Can't wait to see the new board in action. I'd be interested in integrating your design into a SNES motherboard redesign I'm working on for a portable SNES handheld. I was originally making a new 1Chip board, but based off this work, a 3-Chip with digital video out is clearly superior. With a linedoubler and some extra logic implemented in the CPLD (or an fpga if the cpld can't handle it) you could drive a LCD directly and bypass the DAC and LCD driver board for emulator-quality video on original hardware.


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 Post subject: Re: Sharp video output for the 3-Chip SNES using digital sig
PostPosted: Tue Oct 13, 2020 3:22 pm 


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If everything goes as planned I will open source the design. I'd like to see an HDMI mod as well, hopefully someone makes one.


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 Post subject: Re: Sharp video output for the 3-Chip SNES using digital sig
PostPosted: Wed Oct 14, 2020 7:37 am 


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Yesterday I've finished assembling the new board. After a quick test the Mode 7 patch seems to be working and the video is clean and sharp.

More results will follow. I'll try to get some direct video captures.

Image


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 Post subject: Re: Sharp video output for the 3-Chip SNES using digital sig
PostPosted: Wed Oct 14, 2020 12:34 pm 


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Opatus wrote:
Yesterday I've finished assembling the new board. After a quick test the Mode 7 patch seems to be working and the video is clean and sharp.

More results will follow. I'll try to get some direct video captures.

Image

That looks awesome, how exactly does it attach to the mainboard?


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 Post subject: Re: Sharp video output for the 3-Chip SNES using digital sig
PostPosted: Wed Oct 14, 2020 1:33 pm 


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Very excited by this, I'd definitely be interested in trying it out!

maxtherabbit wrote:
That looks awesome, how exactly does it attach to the mainboard?


Looks as though PPU2 is replaced by a socket that the board attaches onto.


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 Post subject: Re: Sharp video output for the 3-Chip SNES using digital sig
PostPosted: Wed Oct 14, 2020 1:55 pm 


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Kez wrote:
Very excited by this, I'd definitely be interested in trying it out!

maxtherabbit wrote:
That looks awesome, how exactly does it attach to the mainboard?


Looks as though PPU2 is replaced by a socket that the board attaches onto.

Yeah I gathered that but what kind of socket attaches to a QFP footprint?


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 Post subject: Re: Sharp video output for the 3-Chip SNES using digital sig
PostPosted: Wed Oct 14, 2020 2:09 pm 


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Here is an image of the previous board, the adatper PCB was not changed. I didn't want to lift 20+ pins so I made an adapter. It is soldered to the QFP footprint like a QFN chip would. Unfortunately no manufacturer could do 0.65 mm edge plating.

Image

As I have only had a PAL SNES I made my mod board based on the dimensions of that mainboard. So it is only directly compatible with the original NTSC revision (SHVC-CPU-XX). But I've made a 2nd adapter board for the other 3 revisions(GPM, RGB, APU). If the mod board is rotated 180° in theory it will fit those. I did not try it yet.


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 Post subject: Re: Sharp video output for the 3-Chip SNES using digital sig
PostPosted: Wed Oct 14, 2020 2:47 pm 


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So the adapter board just has a QFP footprint of its own on the bottom and you have to line it up blind? Was that as bad as it sounds?


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 Post subject: Re: Sharp video output for the 3-Chip SNES using digital sig
PostPosted: Wed Oct 14, 2020 2:57 pm 


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At least it looks like it's easy to check for continuity and shorts.


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