Gamecube Component Cable to VGA - What exactly does the 10k resistor do?

[Link83]

Hi all,
Am hoping to acquire a Gamecube Component cable (Or D-Terminal cable) so that I can do the VGA mod, but I just wondered if somebody could tell me what the 10k resistor needed is actually for? What does it connect to?

Following the Wiki here:-
http://gamesx.com/wiki/doku.php?id=av:nintendodigitalav

I believe leg 12 of the DAC usually connects to ground, but once lifted you connect it to pin 1 via a 10k resistor, but what does pin 1 actually do? Pin1 is listed on the Wiki as "DetectCable (pull high 1.8V)" - whatever that means!

I have read elewhere that the resistor isnt strictly neccesary, but that its highly recommended to prevent static charges from damaging the DAC.

(Also, just a side note but the Wiki lists the Gamecube's Digital port as having 22pins - which is correct - but the connector picture above is numbered 1-20. Shouldnt it be numbered 1-22? If anyone has the original connector picture it could be re-numbered)

[ken_cinder]

If "detect cable', it's probably because you also need a normal AV cable hooked up for audio. So it's probably so the system knows the cable is present, with a normal AV cable already hooked up.

If you're connecting it and throwing a resistor in, it's probably so the system is forced into 31khz mode right on powerup, and the resistor.......well you know what a resistor does.

[Link83]

Hi,
Thanks for your reply, but as far as I understand the Gamecube cant be forced into 31khz/Progressive scan on powerup(?) - it only switches if the software supports it.

I thought the cable detect signal would be for sometihng like that, but if it is why would you connect up leg 12 of the DAC chip to it instead of ground?

Does anybody know who originally came up with the mod that switches the DAC to RGBHV instead of YPbPr? Im just curious to know how they figured it out without using a datasheet. Did they use a datasheet from a similar Macronix DAC and if so which one?

Thanks in advance, and Merry Christamas everyone! 

[NFG]

The mod was figured out by a guy on the old Atarilabs forum.  Oscar, I think.  It's from him that we received the pinout for the Macronix part (which is on the gamesx wiki).  He's long, long gone, so no more information is likely forthcoming.

As for pin 12...  It's a simple hi/lo select.  The resistor is not required (I never use one) and is only there to keep you from shorting out the 1.8V supply accidentally). 

LOW/GND = Component
HI/1.8V = RGB

[Link83]

Thanks Lawrence 
So as soon as pin 12 is lifted it changes to RGBHV, regardless of any resistor?

Can I ask how/why pin 1 is listed as 'cable detect'? Is it actually just a 1.8v line, or does it actually 'cable detect' aswell, and if so how?

...and sorry if im being abit dense here, but how would leaving pin 12 floating possibly short out this 1.8v line? Is Pin 12 of the DAC and Pin 1 of the Connector related/connected somehow internally inside the DAC? and what voltage is pin 12 actually recieving after the 10k resistor?

Its a shame Oscar isnt around anymore, I would love to know how he figured this all out - I dont think its the sort of thing you'd easily discover through trial and error 

Oh, and im not sure if it would be ok for me to change the connector picture on the Wiki, but if so I have edited the picture as best I could to change the pin numbering:-

Im not sure if thats good enough?

[NFG]

So as soon as pin 12 is lifted it changes to RGBHV, regardless of any resistor?

No, as soon as you apply positive voltage to it, it's RGB.  The resistor isn't required, but the high voltage signal is.  Otherwise this input 'floats' which is a kind of not-good nowhere state that the chip may not interpret the way you'd like.  You gotta firmly give it one input or another in most cases (it's just good habit).

1 is called cable detect so the GC knows what kind of cable (RGB/Component) is attached. 

Leaving the pin floating won't affect the 1.8V line, but shorting the bare pin to the top metal chassis of the connector (which is grounded) sure as shit will.  =)

...What was wrong with the old numbering?

[Link83]

So does the gamecube literally 'change' the digital data being fed to the Macronix DAC?

Sorry, the weird name of that pin threw me.  No, the data coming from the system is always the same, the pin changes the output from RGB or Component.

What im really wondering is, if neccessary could you connect up pin 12 of the DAC to any 3.3v pin/source instead, and if so would a 10k resistor still suffice? Or what resistor would I need to lower 3.3v to 1.8v? Up to what voltage is pin 12 'happy' with?

I have no idea why you're asking that, unless you think you've got another place to use this chip?  AFAIK it's unique to the GC (I know of no other hardware that uses the same digital video output, anyway).

Hopefully the pin function list below the picture will still match up with the pin numbering (It should do assuming pins 1 & 2 were numbered correctly originally)

Probably my error with the image, whoops.

[Link83]

Thanks for the replies, but im not sure what happened there! My previous post seems to have disappeared and been replaced by Lawrences answers?

Anyway, aswell as changing the cable into VGA im actually also thinking about trying what Moosmann did here with the N64 at the same time (Half way down page):-
http://nfggames.com/forum2/index.php?topic=2563.0
Non destructively of course.

...but since theres no 1.8v source inside an N64 I wondered what I could use instead.
I still think this mod could actually still work as Moosmann said he double soldered D7 and D8, but having looked at the N64's DAC's some more I think that you could also consider it to have 8 data lines aswell (Just like the Gamecube) the 8th being D-Sync. D-Sync isnt listed on the Macronix DAC (In the Wiki at least) so im making a guess that D0 is possibly D-Sync, just not listed as such.

Also the listing order for the data lines is entirely the opposite of the the way the N64's DAC pinouts are - I think it would probably be better if Pin 1 of the Macronix chip was listed as 'Data 0', working downwards like Viletims N64 DAC pinouts here (Bottom of page):-
http://members.optusnet.com.au/eviltim/n64rgb/n64rgb.html
Keeping them all the same, no? Id be happy to edit the Wiki if its agreed it would be better?

[NFG]

Aw crap, I hit modify instead of reply, I totally didn't notice.  Buttons on this forum theme are in the opposite place as most of my others. 

Terribly sorry.  =(

[Link83]

I just wanted to update this thread as I found some useful info on the Gamecubes Digital Port, and more. Basically I was wondering how Oscar had manged to find out so much information, and had assumed he had sat there for weeks with an oscilloscope studying it.

However, whilst searching for more info I am across a Nintendo patent for the Gamecubes external interfaces which gives the entire pinout for the digital port, aswell as a breakdown of how the video data is sent 

Heres a link to the patent:-
http://www.google.com/patents?id=Rk0NAAAAEBAJ&printsec=abstract&zoom=4&dq=6,609,977

and heres one pic from the patent:-


The patent does seem to confirm that the Gamecubes video is sent as 'YCrCb data' as opposed to the N64 where its 'SRGB data' - so that would explain why Mooseman experienced 'strange images' as the CMPV-DOL chip is expecting a totally different color data format. I guess my original plan isnt worth trying now (Unless the CMPV-DOL can also be reconfigured to accept 'SRGB data' instead)

There is a whole heap more info in the patent which I havent even begun to read yet. I am sure some people here will find it interesting 

Now I have one question I would love answered - how did Oscar figure out that pin 12 of the CMPV-DOL chip switched between RGBHV and YPbPr output? I cant see his original posts an the Atarilabs forum anymore, and the internet archive wont work as its excluded by robots.txt. I 'think' I remember reading that he based the original mod on a Texas Instruments DAC that performed the same functions and had a similar pinout to the CMPV-DOL chip, but does anyone know which Texas Instuments DAC it was?
-----------------------------------------------------------------------------------------------------------------------

Slightly OT but I am amazed there isnt more references made to patent sheets - theres loads and loads of info in them which I have not found anywhere else!

....For instance did anyone know that on the N64 the ENC-NUS and the DENC-NUS chips can be switched to output NTSC or PAL color encoding using a similar hi/low switch pin? (This doesnt alter the 50/60hz AFAIK - just the color encoding) Heres a partial N64 circuit diagram I got from another patent sheet:-


Im am sure we could learn alot more info if someone wanted to study all the patents. ...Maybe I should make a separate topic for them?

[NFG]

Oscar never did tell us how he figured it out, but it's not too much of a stretch to imagine him simply changing the status of the hi/lo pins until something interesting happened.  =)

[viletim]

That patent is really comprehensive. The data stream is significantly different to the N64's digital video make exchanging parts impossible. But there is enough info in there to recreate the GC's video DAC.

According to the patent, pin 1 of the digital video connector (VSEL0) is a general purpose digital input which is pulled low with a pull down resistor (no value specified). Connecting this pin to DAC pin 12, which is presumabely another input (and connected to ground in its default position, no less) doesn't make sense. Unless... what is pin 1 connected to inside the cable PCB normally? From the photos I've seen it looks like nothing.

The digi video connector's data lines hook straight into the audio/video data so I don't think the console needs to know whether there's anything connected or not.

Link83, did you end up getting hold of one of these cables?

[Link83]

Yes I did manage to get one for quite cheap as it had already been modfied into an RGB Scart cable which is currently 'broken'. Basically the person who modified it didnt put enough tape round the cable to secure it in the scart sockets collar, so when it was was plugged in and out of the TV the cable pushed in and out of the plug and eventually broke most of the cable connections - so it should be any easy fix, or I could put it back to a component cable 

Would you like some clearer pictures of the chip, or for me to check any connections?
If it helps there quite a few pictures here:-
http://ramblings.narrabilis.com/wp/gamecube-progressive-scan-cable/

and this ones pretty clear:-
http://ramblings.narrabilis.com/GC/cable-board.jpg

I dont know if any pictures I took would be any better as unfortunately you cant take a picture of the back of the board without destroying the plug