Making SEGA Genesis cartridges

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Mike A:
Thanks for the love.

They do look pretty sweet.

I am really happy with the way they came out.

dmckean:
Good stuff!!

The homebrew carts are my favorite.

PL1:

--- Quote from: pbj on March 01, 2023, 04:24:31 pm ---In other news, I was quietly given some PCB plans for a reproduction board that will supposedly allow a 4MB rom to save to FeRAM. It uses a 74LS74A flip flop and a 74LS139 2x4 decoder. I'm pretending I know what those words mean. I went through many, many PCBs and only found those chips on EA College Football and EA NHLPA93, which are both fairly early EA sports games. So I went ahead and ordered some more from China. 74LS138N and 74HC00N were on tons of Sega / EA / Akklaim boards but I'm too dumb to look at the datasheets and figure out if they're compatible. I'll make one cartridge with sockets and see what works, I suppose. The weird FeRAM chip that literally only Sonic 3 used has also been ordered in bulk.

--- End quote ---
74LS74A flip flop - A flip-flop is a circuit that comes with two stable states and is usually used to store binary data. It works a bit like a push-on/push-off power switch where you can set/reset the current state to on or off as needed.

74LS139 2x4 decoder - When the Enable pin is at logic low, the chip uses 2 inputs (A and B) to select which one of four outputs to set to logic low. (Y0-Y3) The chip contains two of these 2x4 decoders.

74LS138N 3x8 decoder - When the Enable pin is at logic low, the chip uses 3 inputs (A, B, and C) to select which one of the eight outputs to set to logic low. (Y0-Y7)

74HC00N Quadruple 2-Input NAND Gates - This chip has four negated logic AND gates. If both inputs to the AND gate are logic high, the output is logic low. If either or both input are logic low, the output is logic high.

None of these four chips have the same function or pinout.

Scott

pbj:
So, I got my PCBs and components in and made a tester board.

Learn from me - don't use machine pin sockets for 30 year old recycled EPROMs. I've subsequently ordered a ZIF socket I'm going to stack on top of it.

You can also see my high tech "edge beveling machine" in the background which consists of dragging the edge of the cartridge at an angle on sandpaper. This is to make insertion easier and less likely to damage your console.

Anyway, I've got Cave Story booting and playing on a dedicated cart for the first time ever. It's not saving, nor is it displaying the save game icon (hovering floppy disk), which I find very odd. I guess there's some mechanism by which it detects your ability to save. Buried deep on the Cage Story megadrive port website, he mentions that it uses 8kB saves but that he's modded the header to say 32kB to increase compatibility with flash carts. Well, I had, of course, ordered 8kB FeRAM 1608 chips like what I thought was used on Sonic 3. Modifying the header back to say 8kB saves didn't change anything. So I busted out another $20 and ordered a stack of 1808 chips. We shall see.

This PCB was designed on a French forum and they have the Megadrive section walled off. I've registered and begged for access but so far no dice. I'm hopeful that with an 1808 FeRAM chip that this board suddenly becomes compatible with SGDK designed games. What is of slight interest is that the board supports a 4MB rom and saving games. SEGA never accomplished this in the 90s.

:cheers:

Mike A:

--- Quote ---This PCB was designed on a French forum and they have the Megadrive section walled off. I've registered and begged for access but so far no dice.
--- End quote ---

So what did you do to piss them off?

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