Cartridge selector

[Guest who]

I'm trying to make a setup for my Genesis so I can plug in a bunch of cartridges to a single board and then select one at a time so I don't have to keep unpluging and pluging games. The problem is, I need some help figuring out how to make the switcher. I figure some sort of logic circuit will be necesary since it'll be hard to find a 60 or so pin switch. Can someone point me in the right direction?

[NFG]

You should be able to get away with just driving the /OE and /CE lines of the cart port.  This disables the chips in the carts and essentially removes them from the circuit.

[Guest who]

What do you mean by driving the lines? do you mean running them to ground, or just disconnecting them?

[ido8bit]

The /OE and /CE lines enable the ROM chip in the cartridge when held low (connected to GND) and disable it when held high (connected to +5V).  If a cartridge isn't enabled the Genesis can't see it even though it is still physically connected to the bus.  

So cartridge selector is basically a board with several cartridge slots on it.  Each cartrige slot is wired in parallel except for the /OE and /CE lines.  These lines are wired to the swtich that selects the cartidge.

Or you could just by a flash cartridge and load it with the games (only those dumped from cartidges you actually own of course) you want and select from a menu.  Very useful if you don't want to carry around a bag full of cartridges with your Nomad.

[Guest who]

Ok, so all I have to do is run 5volts to the OE and CE lines on the unselected carts?
I honestly didn't think it was that simple, thank you for the fast replies.

[ido8bit]

Basically that's it.  +5V to the /OE and /CE lines on the unselected carts, 0V to the /OE and /CE lines on the selected cart.  The simplest way would probably be to use a 2 pole rotary switch with as many positions as you have slots (eg, 6 position 2 pole switch for a 6 cart slots, 4 position 2 pole switch for 4 carts slots, etc).  

[Guest who]

I went down to the local electronics warehouse, but they didn't have the right card edge connectors or a rotary switch that I found suitable. I looked at flash carts online, but they run about $100 and I have to order from oversea. I have a SegaCD unit, can I put Sega .BIN files (Games that I own, I already have tons of legit games) on a CDR and play them that way? I know that CDRs will run on a SCD (I burned Sonic CD beta) but I don't know much about the boot process or security of the system.

[atom]

I went down to the local electronics warehouse, but they didn't have the right card edge connectors or a rotary switch that I found suitable. I looked at flash carts online, but they run about $100 and I have to order from oversea. I have a SegaCD unit, can I put Sega .BIN files (Games that I own, I already have tons of legit games) on a CDR and play them that way? I know that CDRs will run on a SCD (I burned Sonic CD beta) but I don't know much about the boot process or security of the system.

No. Back when I was into programming for the sega cd I started a project like this but it was too time consuming for me. Itd honestly be easier just to set up a cheap pc connected to your TV for emulation.

[kendrick]

About running Genesis/Megadrive cart ROM images off of a Sega CD? This gets asked pretty often, and the example usually cited is the 5-in-1 pack-in game that has five of the popular cart games on one disc. The problem is that the disc has a custom loader that moves different memory pages in and out of the limited Sega CD RAM, which isn't nearly big enough to hold any of those games.

In order to make that run, you not only have to identify the correct way to divide the BIN or SMD file, but also have a resident app that intelligently switches between these pages. Programming at this level is deliberately outside of the scope of discussion at GamesX, according to Lawrence.

-KKC, who has one of those Honeybee flash units with the floppy drive in front, woo!

[kendrick]

I looked at flash carts online, but they run about $100 and I have to order from oversea.

If using a flash cart solves your problem as much as a cart selector would, might I suggest building your own? I knew I had this link lying around...

http://www.raphnet.net/electronique/genesi...sis_cart_en.php

The flaw in this particular design is that it requires direct programming of the EEPROM chips away from the homebrew cart, and doesn't really allow writing of the ROM from the Genesis cart edge. But given how thoroughly this particular project is documented (PCB layouts in four different formats!) it's a good solution for both the beginner and the seasoned modder.

-KKC, hunting fruitlessly for MMC cards in an SD world.

[Vertigo]

The problem is that the disc has a custom loader that moves different memory pages in and out of the limited Sega CD RAM, which isn't nearly big enough to hold any of those games.

AFAIK the Mega-CD has 1.5MBytes of RAM. You can load Revenge of Shinobi from the menu, then open the CD lid if you're using a MCD2 without any problems. It depends on the size of the game you're loading.

[Guest who]

The flaw in this particular design is that it requires direct programming of the EEPROM chips away from the homebrew cart, and doesn't really allow writing of the ROM from the Genesis cart edge. But given how thoroughly this particular project is documented (PCB layouts in four different formats!) it's a good solution for both the beginner and the seasoned modder.

Yeah, I saw that site when I was searching for flash carts, however, I don't know anything about EPROM programming and I wasn't sure if a flash cart would really do what I was trying to accomplish (switching games easily).

[kendrick]

If your goal is to switch between games without touching the hardware, a flash cart won't help unless there's also a menu program that manages the different ROM images. This isn't a native feature of the item linked above.

-KKC, who just had the worst Chinese food ever.

[MaxDestiny]

Wonder if its possible to modify the sega CD to have more ram for such a thing.  

[Guest who]

Wonder if its possible to modify the sega CD to have more ram for such a thing.

I don't think it works that way, game consoles are designed to only use a certain amount of ram. I would think that if you could add more ram, then an edit to the system bios would be nessesary too.

[Aidan]

Yes, it would be possible. No, programs wouldn't use it, as they'd be completely unaware of it. Even if you edited the BIOS, programs still wouldn't use it. Why? Well, no Sega CD had additional RAM, so no-one bothered writing any code to use it.

In any case, what would that additional RAM be used for?

[kendrick]

I think that the intent was to write a custom Sega CD front-end application that would load cartridge images into said RAM space, presumably off the disc media.

-KKC, who wonders if it wouldn't be more productive just a create a whole new peripheral instead of chopping up a Sega CD like that.

[Aidan]

Oh, in that case, simply just set up a cart with the appropriate amount of RAM set up so that it can be mapped into a suitable spot in the memory map. Once that is done, reboot the system and let the device boot from the cart instead.

Not worth screwing around trying to re-write every game to run from a different location!

[atom]

With your button that selects what cartridge, why dont you just send the reset as well? OHHH I WIN!