The N64 cartridge bus is just a parallel bus. Commercial cartridges may not have included coprocessors, but there isn't anything that prevents them. (Edit: The

The N64 cartridge bus is just a parallel bus. Commercial cartridges may not have included coprocessors, but there isn't anything that prevents them. (Edit: The cartridge bus is set up to be most efficient when reading/writing blocks of memory (address is latched w/ auto-increment). It would still work for accessing devices though.)