Sign in to follow this  
Followers 0
Alkex

megadrive YM2612 fm chip

16 posts in this topic

Hi,

I have access to a few sega megadrives, does anyone know if the onboard YM2612 chip will work on the OPL3  module?

Thanks in advance

Alex

Share this post


Link to post
Share on other sites

Hi Alex,

do you know how to get a (free) datasheet for this chip? If you've luck, the internal functions and the SFR addresses are the same - if not, an adaption wouldn't be worth the effort

Best Regards, Thorsten.

Share this post


Link to post
Share on other sites

I've never owned and only very rarely played with a Megadrive/Genesis.  What is the sound of YM2612 like?

Share this post


Link to post
Share on other sites

from seeing a photo once (on that page with all the yamaha chips) , i think this chip is not surface mount

Share this post


Link to post
Share on other sites

Except from a Sega custom chip, everything is DIP.

To listen genesis(megadrive) files:

Get some GYM files(Genesis/MegaDrive songs dumped to files)

http://www.zophar.net/gym/

Install YMAMP plugin in Winamp 2.x/5.x and play the files.

Share this post


Link to post
Share on other sites

I'm rather sure you need to modify the opl3 module. The Genesis chip had different functions and features compared to the opl2 and opl3. Six concurrent FM channels, the sixth channel can be used as an FM or DAC channel (but not both)

Four operators per channel, 2 timers  and a low frequency oscillator. It is basically closer to the Yamaha DX100 sonic engine specs (not so powerful) but I'm quite sure that it is possible to control the YM2612 under mios/midibox platform.

Although the YM2612 is an ancestor of YM3812 and YMF262 it has a unique FM sound, like other OKI soundchips found in arcade machines. A lot of treasure titles for megadrive demonstrate the excellence of the YM2612, so I think it would be cool to find datasheet and work on a YM2612 module! DAC drums are marvelous in GYM scene :D

Share this post


Link to post
Share on other sites

Yeah, DAC drums, that's what I like the most from my genesis. Note that YMamp should be at 24000 bitrate for the drums to sound the most like the real genesis. I don't know if it should be easier/better to use a real genesis with a custom cartridge:

-You don't destroy the machine

-you have both the PSG and FM chip.

-I think it's easier to control the Z80

Here are  the sound chips:

- PSG (TI 76489 chip) (In my genesis 1 I think it's an OKI instead. Maybe the OKI is the DAC?)

- FM chip (Yamaha YM 2612)

Share this post


Link to post
Share on other sites

- PSG (TI 76489 chip) (In my genesis 1 I think it's an OKI instead. Maybe the OKI is the DAC?)

I don't know what was the purpose of the oki IC's in the genesis, but I'm sure that a 8Kb rom was exclusively dedicated for sound. The real trouble is that the coprocessor Z80 was responsible for controlling the YM and the Texas Instruments PSG. The Z80 is clocked @ 4MhZ, slower than the 18f452. It would be very interesting to reuse a Sega Nomad board (very very small!) by interfacing the Z80 to the pic.

The good thing is that the 68k was clocked at ca. 7Mhz amd programmed in assembly and in C with Amiga or IBM :D 

Share this post


Link to post
Share on other sites

The only thing is that I don't know if the Z80 can be directly controlled. It's just that when you remove a cartridge while the Genesis is on, the picture freezes but the song continues. But, it certainly can because when I play Virtua Racing, the FM sound representing an engine has it's pitch controlled.

Share this post


Link to post
Share on other sites

some internal yamaha doc leaked a while ago:

http://gendev.spritesmind.net/forum/viewtopic.php?t=386&postdays=0&postorder=asc&start=0&sid=7ee4d90fbc4cdc646826dbacfda70e52

also notice the ym2612 is used inside the yamaha dx7 II in conjuction with a 16bit linear PCM dac, so if the YM chip can be bought theres nothing to stop us ? I checked chinese site, stock appears to be low but present. Guess they gladly source it and we dont have to fear fakes as oef yet.

Looky:

I will gladly support such efforts!!!

first off:

http://www.spoogeworld.com/music/instruments/yamaha/DX7IIFDServiceManual.pdf

Share this post


Link to post
Share on other sites

This guy is controlling the chip through the mega drive itself:

Prophet2612 might be a good name!  ;)

Share this post


Link to post
Share on other sites

And heres one with direct control from a keyboard:

Share this post


Link to post
Share on other sites

ok guys, I have a few dozen PCM54 da chips Im willing to give away for participants if we get this rolling, also an idea about a novel output stage.

Share this post


Link to post
Share on other sites

also notice the ym2612 is used inside the yamaha dx7 II in conjuction with a 16bit linear PCM dac, so if the YM chip can be bought theres nothing to stop us ? I checked chinese site, stock appears to be low but present. Guess they gladly source it and we dont have to fear fakes as oef yet.

first off:

http://www.spoogeworld.com/music/instruments/yamaha/DX7IIFDServiceManual.pdf

I can't see the ym2612  in the parts list for the DX7 II.  The ym2612 is only 4 operator FM and the the DX7 is 6 operator FM anyways so it can't be the sound generator chip.

Wouldn't it be easier to write a program to run on a megadrive to control the ym2612 than to try and source the chips and build custom hardware?

Share this post


Link to post
Share on other sites

you re right :(

I don see how i was mistaken , as that ym2604 has the 16bit parallel out. HAHAHA. Nevermind, maybe I was one step ahead of myself and someone is about to release an FPGA core I can use with 16bit out that 'd be cool ...

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0