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The Intellivision was developed using General Instruments parts in the CP1600 microprocessor line. This system in unusual in that it uses a common address and data bus. ROM used in Intellivision carts was designed for use in this system (GI ROM). Unfortunately GI ROM is not compatible with the ROM found in most other systems. To work on the shared bus, they must have an address latch built into the ROM. In addition, to reduce the need for external chip select components, each GI ROM can be programmed to respond to a certain range in the memory map. While this is a handy feature if you have GI ROM available, it makes creating a new Intellivision cart without GI ROM rather complicated - and with the CP1600 line no longer supported, GI ROM isn't readily available.
I was looking for a nice project to give something to the classic gaming community, as I enjoy classic gaming and have made use of much of the information provided by other classic gaming fans. After reading about people's wishes for a device such as the Intellicart, I said, gee, that sounds easy enough, let's go for it. Unfortunately, things were much more complicated than I anticipated. The GI documentation available on the web is flawed in several important ways, specifically in the purpose of the ADAR bus cycle. This is a very important cycle which GI kindly listed as being a NOP as far a ROM was concerned. And they listed it that way in multiple data sheets too. It was battling against this problem that lead me to enlist the aid of Joe Zbiciak, Intellivision Guru and creator of the new Intellivision game 4-Tris and the free Intellivision emulator jzintv. You can learn more about Joe and his projects here. Between us and the De Re Intellivision documentation of the T-card, we were able to figure out the details of the Intellivision bus codes, and I believe that Joe is going to be providing all the details in the future so I'll leave that typing to him. Joe provided a lot of help along the way, including all of the Intellivision software to test various parts of the Intellicart, as well as assistance in algorithm development and tuning for use in the Intellicart. Thanks Joe!
Of course several other people helped along the way. Tim Lindner wrote the Mac version of the Intellicart download software, and did an excellent job formatting the manual. Jason Willis wrote the Windows version of the Intellicart download software. Chris Neiman performed the majority of the playtesting of the prototype Intellicart. And William Moeller and Doug Parsons provided background information and support along the way. Thanks to all of the above people for all of your help in making the Intellicart a reality.
If you'd like to see photos of the various prototypes and of my cart reader, then follow this link.