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| pbj:
So, the mega drive cartridge database is not entirely accurate. Madden 93 has save functionality. This had to be disabled by cutting a bunch of traces and then jumping connections back in to the rom chip. Nothing like buzzing out 42 pins on two pcbs and comparing them…. Jumpers added, cuts made. And here’s the front of this monstrosity. I’m going to switch over to 2MB EPROMs soon, which will eliminate one of these jumper wires. And here’s my reasonably convincing full package. ;D |
| leapinlew:
--- Quote from: pbj on April 02, 2022, 10:30:38 pm ---I considered a pi and a Kade and chose otherwise. We are into retro gaming because it is expensive and inconvenient. --- End quote --- :lol |
| pbj:
So the secret to pulling off old labels from sports games is charcoal lighter fluid. I’m not sure why I bothered with anything else. Let it soak, then just peel it off. Simple Green will etch the plastic so be careful. Anyway, still waiting on those 2MB EPROMs to arrive, so I’m dinking around and finding more games that need a 4MB chip. Here’s Metal Dragon, which is exactly 4MB. A very weird game that rips off elements from many others. But it’s nice to play something new. :cheers: |
| pbj:
So, my 2MB EPROMs arrived. All erasing and burning fine so far. Decided to try putting two roms on one chip and using a physical toggle to select one. And it freaking works! Basically you do the opposite of what I’ve been doing with my jumper wires. You can take 2 1MB roms, bit swap them individually, and combine into a single 2MB rom. Then you burn it. If A19 is wired to B8, you play one game. If it’s pulled high to 5V, it plays the other one. You, unfortunately can’t toggle by leaving it floating. So a two way toggle switch wired to A19, 5V, and B8 and you’re good to go. Here’s my super scientific test where I played it one way, then bent out the chip leg, and ran a jumper wire to 5V. I got Mutant League Football and Road Rash 2, both 1MB roms, working. And…. Guess what, it also works with 4MB chips. Instead of A20 to B9, you do B9 to 5V. Leave A19 wired to B8. I got Mutant League Hockey and Football on the same cart. Football was first padded to 2MB with FF, checksum fixed, and then bit swapped. In theory, you could get four games on a 4MB chip, but I think you’d have to have three toggle switches and, if my math is right, you’d be limited to 512k, 512k, 1MB, 2MB (or if smaller, then padded to that for each slot). For now, I’m just going to leave it at two games with a physical toggle. Maybe I figure out the circuit to switch them by hitting the reset button but it feels like too much rigmarole. In other news, confirmed that saving on a 2MB game (Monster World 4) works perfectly on a donor Troy Aikman Football. Sorry, Troy. :cheers: |
| bobbyb13:
More scientific than I could've pulled off! Super fun stuff and nice work. |
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