YM2203

Aurochs · Dec 12, 2006

http://stech68k.net/index.php?topic=45&page=

The YM2612 is basically two YM2203s shoved on the same die (The second one is slightly more special than that because of the DAC channel). So I wondered, would the datasheet for the YM2203 be sufficiently compatable with the YM2612?

And the answer is a resounding "yes". The register listing on the datasheet is almost precicely the same as the one in sega2.doc. The only major differences I found were below $30: registers $00-$09 (appear to be for controlling a noise generator - these may or may not exist in the 2612), register $21 (TEST in the datasheet but LFO control in sega2), $2A and $2B (DAC control), and $2D-$2F (clock divisors in the 2203, again, may or may not exist in the 2612).

Now what we need to do is hack something up to test out these new registers on real hardware.

drx · Dec 12, 2006

nice find. I always thought it could be some two parts joined together, I mean, it was essentially mirrored (setting the first 3 FM channels is done differently than the other 3 FM channels etc). I wonder how did they modify it so it's possible to put DAC in channel 3.

Sith · Dec 12, 2006

Aurochs said:

The YM2612 is basically two YM2203s shoved on the same die ...
Click to expand...

According to Steve Snake this is NOT the case.

Aurochs · Dec 12, 2006

Yah well Steve Snake is a shitcock.

Link or he didn't say it.

Sith · Dec 12, 2006

Aurochs said:

Yah well Steve Snake is a shitcock.

Link or he didn't say it.
Click to expand...

I have him on msn so no links. :P

And calling the programmer of the best Genesis emulator a "shitcock" doesn't exactly make you look smart.

Aurochs · Dec 12, 2006

But he is a shitcock. He's so full of himself that he can't admit that his emulator isn't perfect.

also http://www.srcf.ucam.org/~rga24/computer/music/index.html

If Snake has the actual YM2612 datasheet, I want to know about it. Otherwise, this one will do fine.

EDIT: And since when was I concerned about looking smart anyway? Check out my trashed topics. You'll see that they're all [010]. Clearly I don't care.

Sith · Dec 12, 2006

Steve Snake: "tell him it is SIMILAR to 2 2203s, but he already HAS the registers documented in sega2.doc"

"and I never said my emulator is perfect. but it's close enough."
Click to expand...

Aurochs · Dec 12, 2006

(The second one is slightly more special than that because of the DAC channel)

I never said that it actually WAS two 2203s. Besides, datasheets are nice, and how we have docs for SSG-EG.

drx · Dec 12, 2006

so I heard that blindly worshipping people makes you look stupid too

Sith · Dec 12, 2006

drx said:

so I heard that blindly worshipping people makes you look stupid too
Click to expand...

Don't give me that crap, I don't worship him.

He's just a good friend and his work speaks for itself.

Snake · Dec 12, 2006

Well, you know, insulting people when they're trying to help you out usually doesn't get you very far.

But since you want to know, and I'm a helpful kinda guy rather than a 'shitcock'...

> (The second one is slightly more special than that because of the DAC channel)

There are a lot more differences than that. The YM2612 is not "two 2203s". It performs similar tasks to two 2203s, and is mostly register compatible - but that's true of most of Yamahas soundchips in the same family. The 2203 can do several things that the YM2612 cannot. Two 2203s + a DAC is actually better than a YM2612.

Having said that the YM2203 needs a seperate DAC to actually operate at all.

If you want info you could just ask

> Besides, datasheets are nice and how we have docs for SSG-EG.

Yes, except the SSG-EG in the YM2612 is broken, which is why Sega tell you not to use it.

Quickman · Dec 12, 2006

'Snake? SNAKE?! SNAAAAAAAAAAAAAAAAAAAAAAAAKE! said:

and I never said my emulator is perfect. but it's close enough.
Click to expand...

Far from it. There are numerous instances of inadequacy, from inaccurately rendering the colours actually used by the Megadrive to assuming anything accessing the 32X reserved area must be a 32X ROM (as opposed to actually emulating how the Megadrive handles such a scenario when the 32X is not present - a 32X ROM has the hardware name set to SEGA 32X or MEGA 32X or something, I don't care to look it up at the moment) to the lack of decent debugging tools. It's better than Gens, yes. It's the best emulator for the Megadrive for casual play at the moment, yes. It is however far from "close enough".

Aurochs · Dec 12, 2006

You disappoint me. Here I was expecting you to bitch and moan at me, and instead you give me this level-headed crap. =(

I'm still willing to bet that if you compared the two chips' dies, you would find that the 2612 looks a lot like two 2203s plus a DAC.

> Yes, except the SSG-EG in the YM2612 is broken, which is why Sega tell you not to use it.

I did not realize this. Gens+ lets you disable SSG-EG, so I though that it worked fine and sega2 was simply incomplete (which it is, heh).

I was actually looking for datasheets because I thought they would go into more detail about the inner workings of the chip than sega2 does. While Yamaha does give timing charts and signal descriptions, these are only useful if you're attempting to build a circuit with it. Their description of FM synthesis is also disappointing.

But we're that much closer now. I may have a hookup for the actual 2612 datasheet; I'll have to look into it a bit closer though.

Tweaker · Dec 12, 2006

I was wondering... What's the SSG-EG supposed to do, anyway? It always eluded me -- even moreso now, since it doesn't even work. =P

Sith · Dec 12, 2006

Quickman said:

There are numerous instances of inadequacy, from inaccurately rendering the colours actually used by the Megadrive...
Click to expand...

A MegaDrive was designed to display its picture on a TV and not a monitor.

Hook up your PC to a CRT tv running Fusion and have another look. :P

Snake · Dec 12, 2006

> inaccurately rendering the colours actually used by the Megadrive

This is actually not the case, as Sith points out. Still, if you prefer brighter colours, that feature has been present for about a year now...

> to assuming anything accessing the 32X reserved area must be a 32X ROM

This is also not true 32X only gets enabled when the cartridge accesses the very specific registers that enable it... like a real system.

> I was actually looking for datasheets because I thought they would go into more detail about the inner workings of the chip than sega2 does.

Yeah, I don't think that stuff actually exists. I guess Yamaha didn't want anybody copying their chips.

Aurochs · Dec 12, 2006

YM2203 datasheet said:

In respect to the square wave sound source, this is compatible with YM2149 (SSG)...
Click to expand...

It's a separate chip apparently. Perhaps that's why it's broken.

EDIT: OSHIT NO IT'S NOT

I have to read the 2149 datasheet before I can get back to you though.

Tweaker · Dec 12, 2006

Sith said:

Quickman said:

There are numerous instances of inadequacy, from inaccurately rendering the colours actually used by the Megadrive...
Click to expand...

A MegaDrive was designed to display its picture on a TV and not a monitor.

Hook up your PC to a CRT tv running Fusion and have another look. :P
Click to expand...

Genecyst seems to get the colors spot on, though...

This is what I've been told, anyway... LOst mentioned it a good fair few times.

Aurochs · Dec 13, 2006

Okay, so Yamaha's datasheets are horribly inconsistent. The YM2149 has a very detailed and excellent datasheet, but the 2203's datasheet sucks balls.

Near as I can gather though, the SSG-EG envelope area in the 2203 is a subset of the 2149's register array. It's four bytes shorter than the 2149, but if you give a direct correspondence ($90 - $00, $9F - $0F), the registers they supposedly cut out from the YM2203 make no sense whatsoever.

EDIT: HOLD UP, ABOVE MAY BE INACCURATE

The YM2149's register array is mapped onto the YM2203's $00-$0F. This is probably for compatability with the SSG. Perhaps both regions control the SSG-EG? Someone with real hardware and a flashcart/SMD will have to check it out.

Vangar · Dec 13, 2006

Hey awesome Snakes here. His emulator WAS used in the Sega Smash Pack, wasn't it? That was pretty awesome.

YM2203

Useful Searches