Cartridge

Cartridge bus

The SoC forwards some memory and I/O accesses to the cartridge bus:

• memory: physical addresses 0x10000 - 0xFFFFF,
• I/O: ports 0xC0 - 0xFF.

To facilitate this, the Memory/IO pin is used:

• When Memory/IO is asserted high, all bus address pins specify the 20-bit linear memory address.
• When Memory/IO is asserted low, bus address pins 0-7 specify the port address bits 0-7, bus address pins 8-15 are low, bus address pins 16-19 specify the port address bits 4-7.

Interrupts

The cartridge bus provides an /IRQ pin which can be used by the cartridge to assert an interrupt.