Vector table swap: Difference between revisions
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The first $80 bytes of the [[68k memory map]] are swappable between the onboard [[BIOSes|BIOS]] and the cartridge's first [[P ROM]]. | The first $80 bytes of the [[68k memory map]] are swappable between the onboard [[BIOSes|BIOS]] and the cartridge's first [[P ROM]]. | ||
On startup or reset, | When the vector tables are swapped, $00~$7F point to $C00000~$C0007F, and $C00000~$C0007F point to the data in the P ROM (if any). | ||
On startup or reset, the first $80 bytes are those found at $C00000~$C0007F, so that the system always starts by executing the initialisation routine. | |||
Right before starting a game, the cart's ROM is swapped in as well as the [[S ROM]] and [[M1 ROM]]. | Right before starting a game, the cart's ROM is swapped in as well as the [[S ROM]] and [[M1 ROM]]. | ||
Revision as of 08:35, 17 July 2012
The first $80 bytes of the 68k memory map are swappable between the onboard BIOS and the cartridge's first P ROM.
When the vector tables are swapped, $00~$7F point to $C00000~$C0007F, and $C00000~$C0007F point to the data in the P ROM (if any).
On startup or reset, the first $80 bytes are those found at $C00000~$C0007F, so that the system always starts by executing the initialisation routine.
Right before starting a game, the cart's ROM is swapped in as well as the S ROM and M1 ROM.
Registers $3A0003 (REG_SWPBIOS) and $3A0013 (REG_SWPROM) are used for this.