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Jamisonia
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So.... Some SNESes output YPbPr.....

by Jamisonia Sat May 05, 2012 9:48 am

http://www.sega-16.com/forum/showthread ... nent-video

http://mikejmoffitt.com/wp/?p=74


For those who prefer not to click links SNESes with the BA6592F encoder found in launch era Super Nintendos output YPbPr. In fact this YPbPr already seems to be formatted correctly, so all one has to do is wireup the pins to component jacks or cables.

Additionally Ziggy and I have spoken about this and according to this thread:

nfggames.com/forum2/index.php?topic=3525.0BA6592F

The BA6592F encoder and the second chip used the S-ENC chip have the same pinout, and in fact may be the same exact chip. Thereby increasing the number of Super Nintendos capable of this mod.

This is very exciting, unfortunatenly this poster does not have such and old SNES, so I cannot verify this mod. I suppose the easiet way to look for a yellowed as hell SNES, and see if it has the chip.
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Re: So.... Some SNESes output YPbPr.....

by AppleQueso Sat May 05, 2012 9:52 am

But why? Won't an RGB Scart cable going through a component transcoder essentially give you the same thing?
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ApolloBoy
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Re: So.... Some SNESes output YPbPr.....

by ApolloBoy Sat May 05, 2012 12:49 pm

AppleQueso wrote:But why? Won't an RGB Scart cable going through a component transcoder essentially give you the same thing?

Older SNESes and Super Famicoms tend to have unusually blurry RGB but they may have a sharper component signal. My Super Fami has the BA6592F encoder and it's a little annoying how blurry RGB and S-video are compared to my modded SNES mini.
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Jamisonia
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Re: So.... Some SNESes output YPbPr.....

by Jamisonia Sat May 05, 2012 1:01 pm

AppleQueso wrote:But why? Won't an RGB Scart cable going through a component transcoder essentially give you the same thing?



An RGB to YUV transcoder costs around what? $100. Cost of this mod, less than $5 depending on how you do it. Jacks would be the most expensive part. I thinking getting component out of the console would be far preferable to any external transcoding.
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Re: So.... Some SNESes output YPbPr.....

by Valkyrie-Favor Sat May 05, 2012 1:14 pm

Now I'm pretty disappointed I got an FC Twin.
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Re: So.... Some SNESes output YPbPr.....

by Ziggy587 Sat May 05, 2012 3:00 pm

Jamisonia wrote:Additionally Ziggy and I have spoken about this and according to this thread:

nfggames.com/forum2/index.php?topic=3525.0BA6592F

The BA6592F encoder and the second chip used the S-ENC chip have the same pinout, and in fact may be the same exact chip. Thereby increasing the number of Super Nintendos capable of this mod.


My oldest SNES has the S-ENC BA6594AF encoder. According to the link above, it "appears to have" the same pinout as the BA6592F, which would mean it also outputs YUV component. It's easy enough to check, but I don't know when I'll get around to it.

One thing I noticed is that the BA69592F encoder is located in front of the cart slot. Every other encoder, including my BA6594AF, is located in back of the cart slot (near the AV out). This leaves me to believe that the BA6594AF most likely doesn't output YUV.

The author of that post linked above was able to contact a manufacture in Hong Kong and get the data sheet for the BA6591AF, but he uploaded it to MegaUpload (which is dead now). If any one here is also a member of that forum linked above, could you post or PM Link83 and ask him if he could upload the datasheet elsewhere?

Otherwise, the only way to find out is to just go ahead and try using the pinout for the BA6592F. But there could also be the (remote) chance that the BA6591AF has a different pinout than the BA6592F, but still outputs YUV. That would be annoying, which is why the datasheet is important.

Any one a member of that forum? I hate to join forums just to PM some one.
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Re: So.... Some SNESes output YPbPr.....

by Drakon Sat May 05, 2012 10:48 pm

From my experience rgb "blur" comes directly out of the ppu chip. I installed a rgb to s-video encoder circuit in both my va5 and va6 model 1 sega genesis systems. The va6 had a much nicer s-video picture with the exact same circuit. The only difference between the va5 and the va6 is the va6 has a newer ppu / vdp. And this was done by bypassing the encoder built into these systems so the blur had to have come from the vdp chip. Also with the snes I wired up a cxa2075 encoder circuit into a few different models. In the onechip snes jr the picture is absolutely perfect and better looking than anything else I have. In my model 1 with the older style ppu it was more blurry using the same video circuit and this was bypassing the original video encoder in both systems.

*edit*

I have the datasheets for both the BA6592 and the BA6591 they had identical pinouts last time I checked. I have older model sfcs that probably contain the necessary chip I just never bothered wiring it up. Honestly the s-video from my snes jr with a cxa2075 encoder kind of blows everything else out of the water. The rgb from that system is equally as perfect. I highly doubt the component video quality from the older model 1s could compare.
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Re: So.... Some SNESes output YPbPr.....

by Ziggy587 Sun May 06, 2012 3:38 pm

So I just checked another SNES that I have, it also has the BA6594AF encoder, but this one has it located in front of the cart slot (like where the BA6592F is located). This, and what Drakon said about the pinout, leaves me to believe that the BA6594AF most likely outputs YUV like the BA6592F does. I'm most definitely gonna check to confirm some time soon.

@ Drakon: Would I be able to get those datasheets from you? I'd like to look at them.

In regards from the things you said about the CXA2075 quality and whatnot, I wouldn't doubt it if the CXA encoders produce a better video output than the S-ENC encoders. But the thing about this is that RGB is difficult to use over here. If one could get YUV directly out of the SNES, that would be so much more simpler. Also, the mod would be so much easier to perform.

But speaking about the quality, one person on the Sega-16 did the mod and posted:

http://www.sega-16.com/forum/showthread.php?20732-Easy-SNES-SFC-YUV-component-video!&p=476496&viewfull=1#post476496 wrote:The video is a little odd to me though. Straight reds, blues and greens are pretty vibrant, but regular graphics tend to look a bit pale. Maybe it's just how SNES is, I haven't played it in a while.


I find it odd that you can pull the YUV straight from the encoder's pins. And actually, when I originally heard about this, for this reason I thought it was bullshit. But, there probably needs to be resistors and/or caps in there... possibly. The datasheets would tell all, assuming they're not in Chinese or Japanese (but at least the schematic could be read). So, I would really like to see those datasheets.
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Drakon
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Re: So.... Some SNESes output YPbPr.....

by Drakon Mon May 07, 2012 8:14 am

datasheets:

http://www.mediafire.com/?2x9erpy79q69o8t

The cxa2075 also outputs s-video. But the quality of the s-video and rgb coming out of the cxa2075 depends on the quality of the rgb going into the encoder. The rgb that goes into the encoder comes straight from the ppu chip(s) in the snes. Newer models of the snes have better ppus and better circuits sending a cleaner image quality rgb into the encoder. What I'm saying is the s-video from my cxa2075 snes jr will probably look better than component video from an early model snes. Of course this is using a crt and not a flatscreen. But still you could always take the rgb from my cxa2075 snes jr and convert it to component video externally, again giving a much better quality picture than the early model snes.

The one datasheet I have is japanese the other is english. The way that encoder works is a bit like the old sony cxa1145. The cxa1145 outputs s-video and then inputs that s-video into other pins to generate composite video. It seems these old rohm encoders output yuv then input that yuv into other pins after passing the signals through a small circuit to generate composite video.
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Re: So.... Some SNESes output YPbPr.....

by Ziggy587 Mon May 07, 2012 10:50 am

Drakon wrote:The one datasheet I have is japanese the other is english. The way that encoder works is a bit like the old sony cxa1145. The cxa1145 outputs s-video and then inputs that s-video into other pins to generate composite video. It seems these old rohm encoders output yuv then input that yuv into other pins after passing the signals through a small circuit to generate composite video.


Thanks for the upload!

Yes, after looking at the datasheet for the 6591, it looks like the RGB comes in and gets converted to component (or Y, BY, RY as the datasheet calls it, assuming it's the same thing as yPbPr). The component outputs go through a small circuit, input back into the encoder, then converted to S-Video and composite. It looks like the 6592 does the same thing, though the external circuits might be slightly tweaked.

The real question is... does the 6594 do the same thing? As I've said, I have two SNESes with the 6594. One has it located where you'd normally find the S-RGB encoder, the other has it in front of the cart slot where the 6592 is located. Finding a datasheet for the 6594 has been impossible! Apparently you can pull the component output right off the encoder, so I guess I'll give that a try first to see if the 6594 actually outputs component like the 91 and 92 do.

After that, I doubt the component out is TV-ready straight from the encoder. Looking in the datasheet for the 6591, it looks like they give a schematic to output to a TV, but I can't make it out entirely. Doesn't matter though, things might have changed between the 92 and 94 versions anyway. I was talking to Jam about this and from what he understands the signal outputs should have an impedance of 75ohms. So I think what we'll have to do is measure the impedance of the component output then try our best to get it to 75ohms. I really don't have great knowledge of this kinda stuff by the way. Anyway, the schem from the 6591 datasheet might be a good place to start, but it's a little confusing.

The first thing I gotta do is find out if the 6594 actually outputs component. I think I'll give that a shot today. If it actually does, then we can go from there.
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