Yet another project on the stack. My Neo-Geo is begging for some hacks. And this BIOS is a great one. The main inspiration in the Universe BIOS (or UniBIOS for short). A custom BIOS that provides awesome features like region protection bypassing. This BIOS is the probably the best available for Neo-Geo hardware, with a single problem: it's not open source. I know it's being a little picky. You can can freely download the 2.3 version firmware, and get the latest 3.0 already burned in an EEPROM for a reasonable price (25 euros). Well you begin to know me, and I just can't go the simple way. I want to develop my own open source Neo-Geo BIOS.
First step: remove the original BIOS
There are basically two technics for mounting a custom BIOS. First one is piggy back, where you basically kill the existing EPROM and solder the new one on top of it. It is meant to be easier, but as name says it: dirty as pig. I prefer the second option: remove completely the old EPROM and replace it by a socket. Any you can plug whatever you like in this socket. So that will be step one, and let's hope not the final step in case I fry the board.
Step Two: Get/Build a proper EEPROM
The Neo-Geo BIOS chip is a 1M bits (64Kx16bits) memory, operating a 5v and with 120 ns access time (TCS31024P-15). There are some trouble to find these kind of memory nowadays. Most of 64Kx16 bits memory are discontinued, you can find bigger or smaller, but hadly the exact stuff. Here comes the main part of project: building a PCB to replace the original EEPROM with two Flash chips. I checked the measurements and it should fit. I just have to figure out the proper layout.
So let's see how this will go.
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