Megadrive 6-in-1 examination...

[Aidan]

I picked myself up one of those Megadrive 6-in-1 miniconsole thingies that are floating around at the moment. I've been investigating it's internals, and have found one or two interesting things.

The device supposedly requires 6V in order to operate. This represents a drawback on the battery powered front, as 6V is a fair amount of battery.  Typically when the device is running from 6V, it requires about 70mA to operate.

The internal logic doesn't appear to require nearly so much voltage however! There's an internal regulator dropping the voltage to 3.3V. The extra voltage appears to be required to operate the audio and video amps instead.

I've managed to bring the external supply voltage down to about 2.03V, and the device will still operate. The audio disappears about 2.4V, as the audio amp seems to require that in order to work.

Once the external supply voltage gets down to about 1.99V, the display RAM seems to suffer corruption, leading to glitches in the display. Bringing the voltage back up to the minimum, and the display comes back again.

Checking things out, the internal regulator appears to drop about 0.2V, so the logic is actually operating on about 1.8V by the time you are approaching the minimum voltage for operation. That also means the power requirement drops significantly, down to about 30mA instead of 70mA. How much of this is because the audio amp is no longer running I don't know!

Next step - see if I can interface into that ROM, and see if I can figure out how the game switching mechanism is working!

[atom]

I checked it out, i didnt know such a thing existed. Seems pretty neat and that is the sexiest controller ive ever seen. Rom swapping might give you a little trouble,  the Mega CD bios has probably been reworked or basically removed since it is only going to load the onboard rom. Dump the rom and check out the header and see what format it is in, if you aren't as l33t with you software as your hardware I of course would be more then willing to check this out for you. We (or you) could simply whip up a new header... OH NO WERE SHARING ROMS CALL THE POLICE!

[Aidan]

The ROM looks to be a standard 44pin device, so I might see if I can lift pin 12 (CE) and try to interface an external ROM in there. Unfortunately, the only ROM I have lying around is a real Megadrive cart, and it supposedly requires 5V in order to operate. We'll see if it works on 3.3V!

[Aidan]

I'd have to dump the ROM to do that, and I don't fancy desoldering all 44pins of a surface mount device! However if the ROM switching mechanism is based around some form of bank switching, then there'd be about 7 ROM headers in there.

[Aidan]

Well, I did desolder all 44pins of it, but I've not got something suitable to dump it. I might see if I can knock together something with a few counters and the parallel port on a PC.

Initial testing resulted in a dead machine. I'm going to try to reverse out the changes, and see if it still works!

[hippy dave]

hi all, just passing through...
i hadn't seen this 6 in 1 thing before, looks cool, i'm quite tempted to get one just for the sake of it.
would be great if it was possible to hack some kind of cartridge port into it - a small one as opposed to full-sized megadrive one would be good. this is assuming that it turns out to be run with a standard game rom image in place of the onboard one... if so maybe give it a port to interface to an existing programmable cartridge, like for gb/gba/ngp etc, if any of them bear the slightest resemblence to the right sort of memory access. :rolleyes:
other than that, what else might you try & sqeeze out of it... rgb video? stereo sound? .... player 2 joypad port :lol:  

[Aidan]

That's what I was trying for when I killed my one! It's dead.

Don't hope for RGB or stereo sound. I'm not sure the provision is there for such things. At least, I couldn't find stereo sound when I did a cursory look over the audio side.

Forget the player two port as well, there just are no traces for such a thing!

[hippy dave]

sorry for your loss at least it wasn't toooo expensive
don't suppose you got any further with dumping the onboard rom?

[Guest]

I greatly suspect hacking this device would not be worth too much effort. As the Megadrive-on-a-chip in Majesco's horrific Genesis 3 proved, these combo-chips are usually very poor. In this case, the audio was godawful ..

Note how only a few games are provided, and pretty early ones. Before more advanced features on the machine were utilized by the games at that time. I would not doubt if games utilizing more advanced features, let's say, the VDP's shadowing and highlighting effects, try to run, they'll fail or crash. Same for other advanced raster effects or games that are too stressful for the 68000 workalike to handle.

The fact that they didn't pick any programs exceeding 512 KB to load onto the ROM chip tells me that they didn't go to any great expense to make these devices high quality.

People on the benheck.com forums have been fiddling with this as well with extremely limited success. It's probably more worth it to just purchase a Nomad with rechargable battery pack, as it's fully accurate and of higher build quality. A fun project might be to take an EPROM, write a program that runs multiple games (selected from a menu in 1 ROM image) and wire to the cartridge slot leads, switching to it when a cartridge is removed.

[Epicenter]

^^^^ Argh, why was I not logged in ..

[phreak97]

you can attach a cart slot.
http://www.benheck.com/Games/Exodus.htm

[Aidan]

Looks to be a very different model however. The one I had did not have the seperate controller chip, and the PCB design was totally different. Yes, there was still the Radica copyright on my system!

Next time I'll be a little more careful with the board and see if I can disable the ROM daughterboard rather than remove it.