I just find this.maybe someone can point it.
MAME
static MEMORY_READ16_START( neogeo_readmem )
{ 0x6a0000, 0x6a1fff, MRA16_RAM },
MEMORY_END
static MEMORY_WRITE16_START( neogeo_writemem )
{ 0x6a0000, 0x6a1fff, MWA16_RAM },
MEMORY_END
FBA neo_run.cpp
SekMapMemory(NeoPalSrc[0], [COLOR=Blue]0x6A0000, 0x6A1FFF,[/COLOR] SM_RAM); // Palette RAM bank 0 always accessed here