The two open I/O slots are for general purpose user I/O, special purpose I/O cartridges (such as IEEE), and have been tentatively designated
for enabling the Z-80 cartridge (CP/M option) and for interfacing to a
low-cost high-speed disk system.
The system provides for "auto-start" of the program in a Commodore 64
Expansion Cartridge. The cartridge program is started if the first nine
bytes of the cartridge ROM starting at location 32768 ($8000) contain
specific data. The first two bytes must hold the Cold Start vector to be
used by the cartridge program. The next two bytes at 32770 ($8002) must
be the Warm Start vector used by the cartridge program. The next three
bytes must be the letters, CBM, with bit 7 set in each letter. The last
two bytes must be the digits "80" in PET ASCII.
The following table lists the various memory configurations available
on the COMMODORE 64, the states of the control lines which select each
memory map, and the intended use of each map.
8K KERNAL ROM
|D000 ||4K I/O |
|C000 ||4K RAM (BUFFER) |
8K BASIC ROM
|X||= DON'T CARE|
|GAME ||= 1|
This is the default BASIC memory map which provides BASIC 2.0
and 38K contiguous bytes of user RAM.