Vector table swap

From NeoGeo Development Wiki
Revision as of 07:37, 28 October 2015 by Freem (talk | contribs) (BIOS -> system ROM)
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to: navigation, search

The first $80 bytes of the 68k memory map are swappable between the onboard System ROM 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 Reg.png REG_SWPBIOS and Reg.png REG_SWPROM are used for this.