In my last post I explained how I managed to open up a SEGA cart. The Master System uses a 28 pin mask ROM, which can be replaced by a 27c series EPROM easily. I’ve seen people building EPROM carts using these chips for Mega Drive.

So, when on opening the Mega Games 1 cart I had I found a 42-pin Mask ROM I was a little confused.

Here’s the PCB.

My thinking is this: The Master System is a 8-bit machine, so the cart has 8 data bits, 16 address bits, V+, GND and some other things, like chip enable.

The Mega Drive is a 16-bit machine however, so it would have 16 data bits and 16 address bits. Doing a bit research that appears to be accurate.

Here’s a schematic of a cart (using two AT49F040 Flash chips) on