Making Genesis carts

[Pyract]

I was wondering if anyone could give me some advice on making my own genesis carts (specifically sonic roms). I want to stick various sonic hacks and betas on to their own physical cart. Could anyone tell me what kind of eeproms I need and recommendations on eeprom programmers?

[Calpis]

27C4096 for 4Mbit games (Sonic 1)
27C8192 for 8Mbit (Sonic 2)
27C160 for 16Mbit (Sonic 3 / S&K)
27C320 for 32Mbit (S3&K although you'd need to build your own complex PCB w/ SRAM circuit)

These ROMs are 16bit except for 27C160/320 which are 8/16 bit; you will need to tie the /BYTE pin to VCC and use A0 as D15 for these.

I *THINK* you can swap the normal game's mask ROMs with EPROM.

To program these you will need a moreso expensive programmer which supports 16bit ROMs. The most economical way would be to purchase a Willem programmer with the 16bit adapter. You can buy it on eBay or from http://www.sivava.com/ or http://www.willem.org/catalog/ or http://www.mcumall.com/comersus/stor...namicIndex.asp

[Pyract]

Thank you very much. I really appreciate the help!

[Stone]

Really it depends on what cart you're going to use ;) If you're using commercial carts then you have to use similar ROMs to what was already in them, but if you're using dev carts then you can use pretty much anything. I have a sega one that takes 8x27C1000 (8 128Kx8 EPROMs, = 8 megabit) and an Advantech one that takes 4x 27C040s (512Kx8, so 4 of them is 16 megabit). There was a bloke on eBay selling them off cheap a little while back, I should have got more while they were available really :banghead:

Or you could make your own cart PCB, it's not that hard :-)

Stone

[cdoty]

Frog Feast was made using 27c400s and commercial cartridges. Most of the cartridges would accept 42 pin roms (27c160/27c320).

[Pyract]

I'll be using commercial carts. I probably should have specified that in my first post..

[Xenepp]

Surely there's a thread here somewhere where someone has done this?

I'm looking for something to do this weekend..

[Piglet]

Back in the old, old, incredibly old school when I was doing stuff on the NES, my then empolyer got hold of about 40 commercial (but totally crap so unsalable) games. EPROMS have mor legs than ROMS (usually). What I would do is thus:

-Get into the NES cartridge. I did this by applying a soldering iron to those wacky shaped screws. On cooling, the screws were loose enough would drop out.

-Cut out the ROM. I did this by actually cutting all the legs and then used pliars and soldeding iron to melt out legs.

-Place A ZIP or such removable socket.

-Rewired 4 legs (the ones that were different) onto the board.

-Cut out a ractangle of plastic since the ROM on top of a ZIF wouldn't fit in the casing. I used a box cutter and then... a soldering iron.

So, I assume you can do the self-same thing with the Genesis.

[TmEE]

on MD its simpler, you only have 1 ROM to deal with.

[selgus]

-Get into the NES cartridge. I did this by applying a soldering iron to those wacky shaped screws. On cooling, the screws were loose enough would drop out.

That's interesting. Never thought of that. What I did back in the day, was to file down a split screwdriver to the shape of the screw head pattern.
--Selgus

[TmEE]

I generally used soldering iron too, until I bought suitable screw bits.

[MottZilla]

Crazy. Why couldn't you just get the security bits? They aren't that hard to find. So TmEE or anyone else, Genesis cartridges containing 16bit mask roms are pin compatible with 16bit eproms generally?

[selgus]

Crazy. Why couldn't you just get the security bits? They aren't that hard to find. So TmEE or anyone else, Genesis cartridges containing 16bit mask roms are pin compatible with 16bit eproms generally?

I've always used split HI/LO 8-bit EPROMS for my Genesis work, as I never modified an exisiting cart to add an EPROM. The boards I used have two sockets.
--Selgus

[Calpis]

Yep, well, 1024,2048,4096,800,160,322 at least, no 320 (not that you'd want to use one!)

[TmEE]

Crazy. Why couldn't you just get the security bits? They aren't that hard to find. So TmEE or anyone else, Genesis cartridges containing 16bit mask roms are pin compatible with 16bit eproms generally?

Pin thats used as VPP on EPROMs is sometimes used as address signal on mask ROMs in MD carts. But other than that, pinout is identical and you put another chip in the cart with no or minimal modifications.

[MottZilla]

Yep, well, 1024,2048,4096,800,160,322 at least, no 320 (not that you'd want to use one!)

No kidding! If I had a 320 I'd be building a Seiken Densetsu 3 or something with it. ;)

TmEE, I'll keep a look out for that if they don't work without modification. Hopefully they won't need any modding.

[l_oliveira]

27C160 and 27C322 are the only ones I am sure have pin to pin compatibility with the SEGA mask ROMs... Funny how they used JEDEC pinouts on all of their roms while Nintendo didn't...

[MottZilla]

I heard Nintendo changed their pinout to make the PCB design easier or smoother or something like that. Personally I think Nintendo just did it to be dicks.

So you're unsure of 8Mbit and 4Mbit pin to pin compatibility? I might put it to the test at some point.

[Calpis]

I suppose boards could vary but I think 8M and 16M boards are exactly the same, 1M-4M have a completely different (all compatible) pinout, but you can use 27C400 on 8/16M boards. 32M boards *should* have A20 instead of VPP/!BYTE because it matches the 27C322.

[retro]

Crazy. Why couldn't you just get the security bits? They aren't that hard to find. So TmEE or anyone else, Genesis cartridges containing 16bit mask roms are pin compatible with 16bit eproms generally?

Back in the days of NES and SNES, they weren't easy to get. That's why Nintendo used them! That said, RS always sold the right screwdrivers - just nobody knew ;-)

A trick people liked to do was get a biro, take the ink bit out, heat it up and press it into the screw head. Let it dry and you have a screwdriver! Sorta.

Funny to think that developers couldn't/wouldn't buy dev carts or shells!