Tag Archives: Repros

Dumping 27C301 EPROMs (Or, How To Build A 27C301 to 27C010 Adapter)

I recently purchased several EPROM prototypes for the original Game Boy. After finding that some of the cartridges had differences from the final versions of the game, I attempted to dump them for preservation purposes before they fell victim to “bit rot“, but was thwarted by an EPROM type incompatible with my shitty Willem programmer. That is, the Toshiba TC571001 and Hitachi 27C301; 1Mbit non-JEDEC compliant EPROMs with the same 2 pins swapped on the pinout. Looking at the pinout, they would actually save some time rewiring with MMC3 NES reproductions.

The shitty programmer

The shitty programmer

To dump them, I created a small adapter out of 2 chip slots that I had lying around.

The Slots

The Slots

To create the adapter, I simply wired two jumpers between the slots as shown in the diagram below; from pin 24 to pin 2 and vice versa.

27C301 to 27C010

27C301 to 27C010

Worked like a charm with the 27C010/1001 settings on the programmer while dumping.

The finished adapter

The finished adapter

Why (Cheap) N64 Reproductions Won’t Be Possible

Here’s a mapper-based NES game:

MMC3 mapper, specifically.

MMC3 mapper, specifically.

You have your ROMs (2 big chips on the top left), CIC (anti-piracy chip – on the top-right), memory mapper (bottom left square chip), and WRAM (bottom right chip). The NES reads the game off of the ROM chips by calling the data it needs from the correct memory banks. Since there aren’t enough address bits (what’s used to select memory on the ROM chips) on the NES to support all the memory on the ROMs, the memory mapper helps the NES read all of the data on the ROM’s higher addresses by managing it’s higher addressable (readable) memory. The ROM chips are just that, read-only memory ONLY.

Now, here’s an N64 game:

But there's less chips! That should be simpler, right?

But there’s less chips! That should be simpler, right?

Here we only have 2 chips; the CIC on the left (the little chip) and the ROM/Bank-switching/Logic chip on the right.

Since chip-making technology advanced greatly between the release of the NES and the N64, Nintendo was able to put more “stuff” into that one ROM chip than ever before, making boards cheaper and simpler to produce, and games harder to counterfeit. The fact that this extra “stuff” is included inside the chip, means that simply removing and replacing the chip with a another reprogrammed one (much like how NES and SNES reproductions are made) won’t work.

So basically, N64 reproductions won’t be possible without expensive custom boards to replicate the logic contained inside the ROM chip. This means no cheap N64 reproductions for you.