ocr: THE MEMORY MANAGEMENT UNIT (Continued) Bits 4 and 5 are the GAME and EXROM sense bits, respectively, which are implemented as bidirec- tional ports as explained above. As inputs, they directly reflect the hardware cartridge control lines GAME and EXROM as used in C64 mode. C128 cartridges do not use EXROM and GAME, so if they are detected in C128 mode, a C64 cartridge is present and C64 mode should be asserted. They have no dedicated C128 function. The operating system mode is set by bit 6, This bit is cleared to zero upon reset and its presence enables all MMU registers and other C128 feature ...
