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PostPosted: Thu Mar 19, 2015 5:09 pm 
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I'm currently trying to put together info for getting various video output methods out of various models of various consoles, and seeing as a lot of this info is out there, just scattered about, I thought I'd start a thread to try to consolidate it. My focus is actually on combining as many output methods as possible simultaneously, so if there are mods that might conflict with each other, I'll mention that as well. I'll put up all the info that I know of, and please feel free to correct me if I'm wrong or add info if I've missed it, but I'm NOT INTERESTED IN CONTINUING THE DRAMA FOUND IN THE SNES COMPONENT MOD THREAD. For now, I'm going to start with the NES, SNES, and N64, since those are the ones I'm most interested in, but if people want to chime in with info for other consoles, or with the other regions of these consoles and the output modes that go with them (PAL consoles, A/V Famicom, SCART, 50/60Hz, etc.). I'll be happy to add it. With that being said, here we go.

NES
===Front Loader===
HDMI: Hi-Def NES mod

RGB: Several mods available

Component: NESRGB mod with Component add-on

S-Video: NESRGB mod supports S-Video output

Composite: Supported out-of-the-box, but if you're modding anyway, NESRGB mod supports composite output

===Top Loader===
Same as for the front loader, except composite output is not available out of the box

SNES
Currently, I'm not sure about the differences between the different encoders with respect to output modding, so for now I'm going to just lump them together into "original model" and "mini/jr model"
===Original Model===
HDMI: N/A

RGB: Supported out-of-the-box, but better results can be achieved via an amp bypass mod

Component: Down the rabbit hole

S-Video: Supported out-of-the-box

Composite: Supported out-of-the-box

===Mini/Jr. Model===
HDMI: N/A

RGB: Not connected to the multi-out, but it can be tapped from the encoder, along with the addition of an output amp

Component: Down the rabbit hole

S-Video: Not connected to the multi-out, but it can be tapped from the encoder

Composite: Supported out-of-the-box

N64
Currently the only difference that I know of between the models is that the model with the VDC-NUS DAC (not AVDC-NUS) can be tap RGB directly off the DAC instead of needing the external mod. If there are more differences, let me know and I'll split this up more

HDMI: Not available yet, but marshallh is working on a mod to enable HDMI output

RGB: Can be tapped from the VDC-NUS DAC, or through the N64RGB mod for other models

Component: ???

S-Video: Supported out-of-the-box (all models?)

Composite: Supported out-of-the-box


Last edited by qwertymodo on Thu Mar 19, 2015 10:49 pm, edited 1 time in total.

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PostPosted: Thu Mar 19, 2015 6:26 pm 
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All regions of the original SNES/SFC model support RGB through the multi-out.

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PostPosted: Thu Mar 19, 2015 10:49 pm 
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Thanks for the correction, it makes more sense now why the amp bypass mod requires you to lift pins on the DAC, and come to think of it, I do recall hearing about people using SCART cables with SCART->component converters to get component on unmodified USA consoles, which would imply RGB from the multi-out. Fixed it in the OP


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PostPosted: Fri Mar 20, 2015 5:58 am 
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qwertymodo wrote:
RGB: Can be tapped from the VDC-NUS DAC, or through the N64RGB mod for other models


Geeze, seems like it would be cheaper to just buy an older N64.


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PostPosted: Fri Mar 20, 2015 8:10 am 
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Yeah, I don't know why those boards are so expensive, the PLD is like $6US, and the HDL code is dead simple. You could do it with 4 discrete logic IC's. It's also too bad that he used a discrete R2R ladder rather than a real video DAC for both that and the NESRGB.


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PostPosted: Fri Mar 20, 2015 8:47 am 
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1% resistors are a lot cheaper, and adequate precision for a 6-bit DAC (2¯⁶≈1.5% (edit: fix braino)), than a video DAC.

I know because I looked into this :/ There was a brief period where I was seeing video DACs for ~2-3$ at which point it was probably worth it to avoid the extra analog futzery... but for the past year or so I basically can't find a multichannel video DAC for less than $4-$6, even in bulk.


Last edited by lidnariq on Fri Mar 20, 2015 1:37 pm, edited 1 time in total.

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PostPosted: Fri Mar 20, 2015 1:01 pm 
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I haven't done the calculations, but Wikipedia seems to indicate 1% resistors are only sufficient for 5 bits. The N64 DAC is 7. It's a shame too, if 2% was sufficient, this would be perfect

Edit: Did the math, 2-6=1.5625%, not sure where you came up with 3%, but in that case, Wikipedia is wrong and 1% is sufficient for 6 bits. 2-7=0.78125%, so 1% is close, but technically you need 0.5%


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PostPosted: Fri Mar 20, 2015 1:55 pm 
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Location: NE Indiana, USA (NTSC)
Do N64 games use all 7 bits, or do they use a 5-bit-per-channel frame buffer? I seem to remember a bunch of banding during fades in and out in Mario Kart 64. Star Fox 64 and perhaps other games work around it by blending a small amount of noise across the screen during fades.

Can you get away with wider tolerance resistors for the less significant bits?


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PostPosted: Fri Mar 20, 2015 3:34 pm 
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I expect most games use 5 bits per channel, since 8 bits per channel would double the size of the frame buffer.

qwertymodo wrote:
It's a shame too, if 2% was sufficient, this would be perfect
The datasheet claims accuracy to within half of the least-significant bit. It sounds like 2% is an overall accuracy, and the individual resistors are designed (and/or laser-trimmed) to be accurate relative to each other.


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PostPosted: Fri Mar 20, 2015 3:56 pm 
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Huh, I missed that part of the datasheet... that's pretty awesome. Now the only problem is finding a distributor that actually *sells* the dang things. I may have to order a set of samples just to get my hands on some.


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PostPosted: Fri Mar 20, 2015 5:34 pm 
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Ah, heck... I just looked into it, and I can totally pull off that N64RGB for under $5 in parts (maybe less, if I can find a supplier for those TTE resistors), plus the PCB. That Altera chip is way more expensive than a comparable Xilinx one that can do the same thing for ~$1.20 at single-unit pricing. I see somebody's already done it with the XC9536XL but they didn't include an output amp like the etim one, just the R2R directly driving the signals, which probably doesn't look as good. Combine the two designs and you'd have a real winner. I may have to open-source a board on OSHPark.


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PostPosted: Fri Mar 20, 2015 5:39 pm 
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What's the protocol? Just a single parallel bus with separate strobes for R/G/B ?

R2R DACs are fine as long as 1- there's no significant digital-analog crosstalk and 2- they can source enough current.

Here's a simple single-transistor voltage buffer that gives fairly linear results, and allows you to use a high-precision 10k/20k resistors:
Attachment:
r2r-dac-emitter-follower.png
r2r-dac-emitter-follower.png [ 2.58 KiB | Viewed 3134 times ]
The 20k and 3.5k fine tune everything: their parallel resistance (Thévenin resistance) determines the magnitude of the resulting output; their Thévenin voltage determines whether the output clips (needs to not be too high or too low). Obviously they'll change in a 3V system, and my numbers are not quite right here, either. (the 75 is the input impedance of the television; the funny white stripy thing is a delay line, i.e. the video cable)


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PostPosted: Fri Mar 20, 2015 9:49 pm 
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Actually, I think rather than re-inventing the wheel, I'm going to try and build an RGB/Component board, since I haven't found any N64 component mods. The RGB portion is already pretty straightforward, and this looks like a fairly simple RGB-to-Component circuit.


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PostPosted: Mon Mar 23, 2015 1:16 am 
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qwertymodo wrote:
Ah, heck... I just looked into it, and I can totally pull off that N64RGB for under $5 in parts (maybe less, if I can find a supplier for those TTE resistors), plus the PCB. That Altera chip is way more expensive than a comparable Xilinx one that can do the same thing for ~$1.20 at single-unit pricing. I see somebody's already done it with the XC9536XL but they didn't include an output amp like the etim one, just the R2R directly driving the signals, which probably doesn't look as good. Combine the two designs and you'd have a real winner. I may have to open-source a board on OSHPark.


If you're going to do it, the VHDL model I made for decoding the N64's VGA output is going to be a lot better to synthesize than a schematic capture, so feel free to use it and do some pin mapping.

Maybe this is a good time to talk about this: http://mikejmoffitt.com/articles/0035-n6480.html I didn't make a thread about it since I did not think anyone would care but maybe someone can find it useful for something.

Image

Working on DVI output here and there, though it's not a priority of mine. 480p Component is possible if I can find a synthesizable RGB -> YCbCr component (I'm not bothering with that on my own and simulation-only models are useless).

Also, I have to plug my old Neo-Geo VGA project: http://mikejmoffitt.com/articles/0034-neovga-rev2.html
Image


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PostPosted: Mon Mar 23, 2015 6:22 am 
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mikejmoffitt wrote:
If you're going to do it, the VHDL model I made for decoding the N64's VGA output is going to be a lot better to synthesize than a schematic capture, so feel free to use it and do some pin mapping.
That reminds me. Is the video signal really 7 bits per component? Your VHDL (as well as every other design I've ever seen) suspiciously ignores three bits...


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