Having a 16-bit address bus, the Z80 CPU allows access to 64KiB of memory at most. In NeoGeo cartridges, the NEO-ZMC or NEO-ZMC2 chips provide a way to access more memory for bigger M1 ROMs. Four different switchable zones ("windows") are available in the Z80 memory map.
The banks are configured by reading from some of the Z80's ports (see page for explanation).
Bank offsets numbering depend on the zone:
- Zone 0 counts in 2KiB increments
- zone 1 in 4KiB
- zone 2 in 8KiB
- zone 3 in 16KiB
The NeoGeo CD doesn't allow for Z80 bankswitching.
This simply maps Z80 $0000~$F7FF to M1 ROM $0000~$F7FF linearly, with no gaps.
ld a,$1E in a,($08) ; Set zone 0 at $1E*$800 = $F000 ld a,$0E in a,($09) ; Set zone 1 at $E*$1000 = $E000 ld a,$06 in a,($0A) ; Set zone 2 at $6*$2000 = $C000 ld a,$02 in a,($0B) ; Set zone 3 at $2*$4000 = $8000
The King of Fighters '97 does this:
; 32KiB bank number in A rlca rlca ld e,a ld d,$00 ; DE = A * 4 (table entry size) ld hl,$289C ; Table address, see below add hl,de ld a,(hl) in a,($08) ; Set zone 0 inc hl ld a,(hl) in a,($09) ; Set zone 1 inc hl ld a,(hl) in a,($0A) ; Set zone 2 inc hl ld a,(hl) in a,($0B) ; Set zone 3
The table at $289C is used to set the 4 zones like an unique $7800-bytes long one in 32KiB increments, meaning that $800 bytes are wasted at the end of each range (mapped to Z80 RAM).
Data at $289C: 1E 0E 06 02 = F000, E000, C000, 8000 "Big bank 0": $8000~ $F7FF ($F800~ $FFFF is wasted) 2E 16 0A 04 = 17000, 16000, 14000, 10000 "Big bank 1": $10000~$177FF ($177FF~$17FFF is wasted) 3E 1E 0E 06 = 1F000, 1E000, 1C000, 18000 "Big bank 2": $18000~$1F7FF ($1F7FF~$1FFFF is wasted) 4E 26 12 08 = 27000, 26000, 24000, 20000 "Big bank 3": $20000~$277FF ($277FF~$27FFF is wasted) 5E 2E 16 0A = 2F000, 2E000, 2C000, 28000 "Big bank 4": $28000~$2F7FF ($2F7FF~$2FFFF is wasted) 6E 36 1A 0C = 37000, 36000, 34000, 30000 "Big bank 5": $30000~$377FF ($377FF~$37FFF is wasted) 7E 3E 1E 0E = 3F000, 3E000, 3C000, 38000 "Big bank 6": $38000~$3F7FF ($3F7FF~$3FFFF is wasted)
Note that the game has a 128KiB M1 ROM, but the table is long enough to map up to 256KiB.
Bank settings at boot on a cartridge system, confirmed using Z80 ICE: