soniccd123
commented
3 years ago The switches select the first address the Genesis will look in the ROM chip when it is booting up. By manipulating which address is the first one, the system can boot up at diferent parts of the ROM, with the condition that there is bootable code there.
With just one game, all switches must be on, so the first address is 0x0, when a switch is on it connects the respective address lines to the Genesis so it can control the said addresses on the ROM, when the switch is off, the respective address line is disconnected from the Genesis and said line is pulled high in the ROM chip.
The combinations depends on the size of the games you use on the multicart, for example, a 1MB game and a 512kB game in the same chip: the 1MB is on the beggining of the chip, so all switches on. Then the 512kB game is right after the 1MB one, so you must consider that it is 4x 256kB banks after the start of the chip, so, switch A19 off, so the first address that the Genesis look at is after the first MB of the ROM (0x100000).
Don't know if this is clear, I know that some of these concepts may not be fully intuitive, If you need help with that, don't be afraid to ask :)
Very new here so sorry if this is not how I should be asking but:
Im confused by the dip switch situation. If I run only one game on the ROM do I have all switches on or off? or some kind of combo. Also with a multi game cart, assuming I ran a game each 256k bank, what would all the combinations be?
Thanks for your time and this amazing project you gave us =)