32X S-viedo mod

[blackevilweredragon]

Ok, surely this mod exists somewhere, or it's possible...

I've poked around in my 32X, and I accidentally poked one pin, that had just luminance on it (i forget which pin now though)..  since i found this, surely there has to be a chrominance only line somewhere in it..

I can't do any mod that requires RGB to S-video..  just don't have the money--literally..

is anyone aware of a mod to do this?

[ido8bit]

As far as I know the only way to get S-video out of the 32X is to encode it from the RGB output with a CXA1645 or similar.  The video encoder used by Sega in these systems simply doesn't generate the Y/C signals.

[blackevilweredragon]

ok, what game systems contain a CXA1645?  i'll just take it off one of them..

[blackevilweredragon]

Ok..  I may get a CXA1645M for christmas...

While I know how to power it (i'll power it from the 32X's 5v output on the AV connector), and will use the 32Xs RGB and composite sync, but what I don't get:  What is the subcarrier?  And how do I introduce this into the chip?

I want it to also be able to output PAL 50, and NTSC 60...  (well, PAL 50 isn't high priority, but NTSC 60 is VERY high priority)...

thanks..

actually, any schematics on how to do this?  im looking at the datasheet, and it seems a little more complicated...

[NFG]

The subcarrier is the colour clock frequency.  You need a crystal/oscillator to create the subcarrier.

It's not really easy to put this chip in a cable, as you seem to be planning.  

[blackevilweredragon]

The subcarrier is the colour clock frequency.  You need a crystal/oscillator to create the subcarrier.

It's not really easy to put this chip in a cable, as you seem to be planning.

oh i know that..  im gonna put it in a box that sits external to the 32X..  but it will be powered from the AV out..

I just ordered a free sample AD725 from Analog Devices (still waiting to see if im approved)...  So, i'd imagine it would be the same for that chip though, right?

[GZeus]

You mean you royals can be poor too?

As Lawrence would say "read the wiki, this forum is not here for you to ask questions that have already been answered elsewhere. You should do your own research."

[blackevilweredragon]

I want S-Video for the big screen...

The pinout for the analog devices make no sense..  They tried to explain it, but they fail to mention WHICH crystal you need for NTSC or PAL...

[GZeus]

I want S-Video for the big screen...

The pinout for the analog devices make no sense..  They tried to explain it, but they fail to mention WHICH crystal you need for NTSC or PAL...

To my knowledge, the carrier frequency is the same as the SMS' Z80 clock.
3.54mhz is that, but that is what I'd heard.

I have no idea why this was deleted.


http://en.wikipedia.org/wiki/Sega_Game_Gear#Specifications
That's where I got it. a game Gear is an SMS, and getting TV-out from a Game Gear is simple.

[blackevilweredragon]

I want S-Video for the big screen...

The pinout for the analog devices make no sense..  They tried to explain it, but they fail to mention WHICH crystal you need for NTSC or PAL...

To my knowledge, the carrier frequency is the same as the SMS' Z80 clock.
3.54mhz is that, but that is what I'd heard.

I have no idea why this was deleted.


http://en.wikipedia.org/wiki/Sega_Game_Gear#Specifications
That's where I got it. a game Gear is an SMS, and getting TV-out from a Game Gear is simple.

hmm, i got a crystal that is EXACTLY 4 times that..  maybe if I can divide it, it'll work..

[NFG]

I have no idea why this was deleted.

Because the first time you called him a jackhole.

[blackevilweredragon]

ok, i got a circuit set for when the chip arrives..

only thing i can't figure out, which pin do I put the 5v from the 32X into?  the APOS, or the DPOS?  I have no idea what the difference is..

APOS = Analog 5V
DPOS = Digital 5V

oh, and on a 2-pin oscillator, which side do you feed the 5v, and which side is the CLK output?  (i've never used a 2-pin before)

[NFG]

clocks are outside of my experience, but it seems to me a 2-pin crystal requires additional components to make a clock signal, where a 4-leg unit has those components built in.

[blackevilweredragon]

clocks are outside of my experience, but it seems to me a 2-pin crystal requires additional components to make a clock signal, where a 4-leg unit has those components built in.

ok..  i'll have to find a 4-pin clock that can give the 14MHz signal (according to Analog Devices, it must be 4X the normal carrier)

[GZeus]

I have no idea why this was deleted.

Because the first time you called him a jackhole.

Oh yeah.
THANKS.

[viletim!]

blackevilweredragon,

The AD725 requires an external oscillator, you can't to simply connect a crystal and a pair of small capacitors like the AD724 and CXA varieties allow. There is a circuit for a suitable oscilator (and it's super simple) in the datasheet so that shouldn't be a problem. They use a crystal of four times the carrirer frequency because aparently you get better accuracy when you use a higher frequency and divide it down than a crystal that resonates at desired subcarrier freq (which is what most game consoles end up doing anyway).

I have a feeling the AD72x arn't suitable for encoding the video from a 32X. I say this because they require the horizontal sync pulse length to be accurate to the NTSC (or PAL) standard. The Megadrive's video output has a slightly elongated sync pulse which puts it out of spec (only slightly, it won't bother any TV). As a resault the AD72x encoders can't be used for the Megadrive (at least, not without an extra circuit to fix the sync) and it's quite possible that it can't encode the 32x's video for the same reason. I don't have any games for my 32X so I can't check myself.

And it's quite normal for a mixed signal IC (one that is part analogue, part digital) to have seperate power supply pins for their respective parts of the chip. When working with more complex circuits it's handy to be able to power all the analogue and digital stuff seperately so the switching noise from the digital power rail doesn't get into the analogue circuits via the power supply. In your case jou can just connect two pins together.

[GZeus]

clocks are outside of my experience, but it seems to me a 2-pin crystal requires additional components to make a clock signal, where a 4-leg unit has those components built in.

It's possible to get a signal from that kind of a circuit, it just sucks to work with compared to a 3 or 4 conductor type. the ground being shared in active pickup circuits is an equally annoying step to going to 2 conductor. Well, parhaps only 50% as annoying.
An Irish pennant inside a guitar/bass can cause a crackle, but if your ground is shared signal and voltage it's a damned loud crackle! Speakers ain't cheap, so I always tin carefully...

Ground is generally used as a negative voltage line in digital circuits, but a clock puts out an analog signal, a square wave, generally.
The general idea is an ideal situation is 4 leads: positive voltage, negative voltage, positive signal, and negative signal.
Voltage lines are going to be DC and the signals AC.

Adding DC to an AC signal simply alters the bias(more positive or negative in the swing more or less).
The fact that these clocks to anything tells me that it's probably sharing the clock and signal out lines. In fact, that's the only way it can work.
You're going to end up with song noise in your grounding unless you filter that, and/or you'll have to use a cap to restore the bias. I don't know the values, because I'm not sure what line the voltage is attached to(no clocks handy, though I have a few about).

[GZeus]

The idea that dividing down VS using the most accurate clock makes sense. You're left with more fundamental and less noise in most cases outside of digital gear. Hiss is ignored by the 'tracking' in a good circuits.

[blackevilweredragon]

well the Genesis runs on a clock that gets divided..  MANY times too, and to different speeds at that..  yet it works..

[GZeus]

well the Genesis runs on a clock that gets divided..  MANY times too, and to different speeds at that..  yet it works..

yeah... that's what I said, more or less...

You're a confused individual, aren't you?
I recommend not drinking caffiene, or at least cutting back if you're a pot-a-day drinker.
Not everyone can handle that.
I know I can't. SOMETIMES i drink a cup or two.

[blackevilweredragon]

let's keep it on topic, shall we?

[GZeus]

let's keep it on topic, shall we?

I'd LIKE to, but I'd also like to not repeat myself or have people repeat what I've said as though it's the opposite.