Memory mapped registers

Note: Most of the register names come from neogeo_spex.pdf

Common registers

I/O registers

Address	Name	Size	Read	Write	Handled by
$300000	REG_P1CNT	Byte	Player 1 controls (active low) Bit 7 6 5 4 3 2 1 0 Def D C B A Right Left Down Up	?	NEO-C1
$300001	REG_DIPSW	Byte	Dipswitches (active low) Bit 7 6 5 4 3 2 1 0 Def Freeze Freeplay Coin meters ? Autofire ? Test mode	Kick watchdog	NEO-F0 (read)
$300081	?	Byte	Read only	?	?
$320000	REG_SOUND	Byte	Send command to Z80	Read Z80 reply code	NEO-D0 ?
$320001	REG_STATUS_A	Byte	Bit 7 6 5 4 3 2 1 0 Def ?	?	?
$340000	REG_P2CNT	Byte	Player 2 controls (active low) Bit 7 6 5 4 3 2 1 0 Def D C B A Right Left Down Up	?	NEO-C1
$380000	REG_STATUS_B	Byte	Bit 7 6 5 4 3 2 1 0 Def ? Memory card write protect Memory card inserted Select P2 Start P2 Select P1 Start P1	?	NEO-C1
$380001	?	Byte	?	Joypad ports outputs Bit 7 6 5 4 3 2 1 0 Def ? P2 outputs P1 outputs MAME select_controller	NEO-D0
$380011	?	Byte	?	Write only, after a write to $3A0019	?
$380021	REG_SLOT	Byte	?	Bit 7 6 5 4 3 2 1 0 Def ? Slot #	NEO-F0?
$380030(1?)	?	Byte	?	MAME set_output_latch (LED marquee ?)	NEO-F0?
$380040(1?)	?	Byte	?	MAME set_output_data (LED marquee ?)	NEO-F0?
$380050(1?)	?	Byte	?	MAME upd4990a_control_16_w (Calendar)	NEO-F0?
$380061	?	Byte	?	Base address for writes (used by the MVS BIOS)	?
$380065	?	Byte	?	Write only (used by the MVS BIOS)	?
$380067	?	Byte	?	Write only (used by the MVS BIOS)	?

System registers

Handled by a 74HC259 adressable latch.

Address	Name	Size	Read	Write
$3A0001	REG_DISPENABL	Byte	Invalid	Normal video output
$3A0011	REG_DISPDSABL	Byte	Invalid	Darken video output
$3A0003	?	Byte	Invalid	Use the BIOS vector table
$3A0013	REG_SWPROM	Byte	Invalid	Use the cart's vector table
$3A0005	REG_CRDUNLOCK1	Byte	Invalid	Allow /WE to pass through to memory card when low
$3A0015	REG_CRDLOCK1	Byte	Invalid	Don't allow /WE to pass through to memory card
$3A0007	REG_CRDLOCK2	Byte	Invalid	Don't allow /WE to pass through to memory card
$3A0017	REG_CRDUNLOCK1	Byte	Invalid	Allow /WE to pass through to memory card when high
$3A0009	?	Byte	Invalid	?
$3A0019	?	Byte	Invalid	?
$3A000B	REG_BRDFIX	Byte	Invalid	Use the embeded fix tileset (SFIX)
$3A001B	REG_CRTFIX	Byte	Invalid	Use the cart's fix tileset
$3A000D	REG_SRAMLOCK	Byte	Invalid	Write-protects the SRAM (MVS)
$3A001D	REG_SRAMULOCK	Byte	Invalid	Unprotects SRAM (MVS)
$3A000F	REG_PALBANK1	Byte	Invalid	Use palette bank 1
$3A001F	REG_PALBANK0	Byte	Invalid	Use palette bank 0

Video registers

Probably handled by the LSPC chips.

Address	Name	Size	Read	Write
$3C0000	REG_VRAMADDR	Word	Read VRAM (address isn't changed)	Sets VRAM address
$3C0002	REG_VRAMRW	Word	Read VRAM (address isn't changed)	Write VRAM
$3C0004	Word	REG_VRAMMOD	Reads VRAM address modulo	Sets VRAM address modulo (signed)
$3C0006	REG_HBLANKCNT	Word	Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Def Raster line counter ? 1:50Hz 0:60Hz Auto animation counter Line counter: (diagram needed) $00F8-$00FF : Vertical sync $0100-$010F : Top border $0110-$01EF : Active display $01F0-$01FF : Bottom border	Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Def Auto animation speed (in frames) HBlank (RLI) interrupt mode HBlank interrupt enabled Disable auto animation ?
$3C0008	REG_HBLANKPOS	Word	Invalid	MSB of RLI position (number of pixels)
$3C000A	?	Word	Invalid	LSB of RLI position (number of pixels)
$3C000C	REG_IRQACK	Byte	Invalid	Interrupt Acknowledge. Bit 7 6 5 4 3 2 1 0 Def ? Ack VBlank Ack HBlank Ack IRQ3
$3C000E $3C000F	?	?	Some emulators treat these locations like $3C000A.

NeoGeo CD only (from NeoCD's source)

NEO-MGA / LC8953 ?

Address	Name	Size	Read	Write	Handled by
$FF0002	?	Word	?	?	?
$FF007E~$FF008F	?	Word	?	dma_mode
$FF0105	?	Byte	?	upload_type_w
$FF0111	?	Byte	?	spr_disable
$FF0115	?	Byte	?	fix_disable
$FF0119	?	Byte	?	video_enable
$FF011C	?	Word	region_code, 0xFF	?
$FF016F	?	Byte	?	disable_irq_w
$FF0183	?	Byte	?	z80_enable
$FF0188	?	Word	REG_CDDALEFTL	?	NEO-MGA
$FF018A	?	Word	REG_CDDARIGHTL	?