rallyrabbit Posted January 5, 2019 Share Posted January 5, 2019 Hi All, I've been reading this forum a long time and finally started working on my 2600 clone game console since my 2600 died. If I am reading the schematics right, we have A1-A11 tied to the chips through the cartridge connector and the 8 data lines D1-D8. This should mean we have a 2k mappable ROM space. However, in looking at the schmatics more, we seem to have 2 Chip Selects. 1 is typically tied down to the Atari CPU and would assume it is used in a standard way to select the ROM chip when addresses A1-A11 are used. This seems to be active low. Curious is the other CS (EXROM) (also active low), which in all the sample cartridges that I found is tied to VCC, I am trying to understand a bit more about how we get >2k ROM given the schematics I've seen. Quote Link to comment Share on other sites More sharing options...
+SpiceWare Posted January 5, 2019 Share Posted January 5, 2019 Cartridge port pinout is A0-A12, not A1-A11. A12 is used to select the cartridge port. This means if A12 is 0 the internals of the 2600 are being accessed, if it's 1 then the cartridge is being accessed. That leaves A0-A11 to select an address from within the cartridge. That's 12 address lines, not 11, and 2^12 = 4096 unique addresses to select from. Quote Link to comment Share on other sites More sharing options...
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