Memory mapped registers

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

I/O registers

Always read/written as bytes (?)

Address	Name	Read	Write	Handled by
$300000	REG_P1CNT	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	Dipswitches (active low) Bit 7 6 5 4 3 2 1 0 Def Freeze Freeplay Multiplayer configuration Controller mode (normal or mahjong) Coin mode (normal or versus) Test mode	Kick watchdog	NEO-F0 (read)
$300081	?	Read only	?	?
$320000	REG_SOUND	Send command to Z80	Read Z80 reply code	NEO-D0 ?
$320001	REG_STATUS_A	Bit 7 6 5 4 3 2 1 0 Def NEC D4990 data bit NEC D4990 time pulse ? Service Coin 2 Coin 1	?	?
$340000	REG_P2CNT	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	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	REG_POUTPUT	?	Joypad ports outputs Bit 7 6 5 4 3 2 1 0 Def ? P2 outputs P1 outputs MAME select_controller	NEO-D0
$380011	?	?	Write only, after a write to $3A0019	?
$380021	REG_SLOT	?	Bit 7 6 5 4 3 2 1 0 Def ? Slot #	NEO-F0?
$380030(1?)	?	?	MAME set_output_latch (LED marquee ?)	NEO-F0?
$380040(1?)	?	?	MAME set_output_data (LED marquee ?)	NEO-F0?
$380050(1?)	?	?	MAME upd4990a_control_16_w (Calendar)	NEO-F0?
$380061	?	?	Base address for writes (used by the MVS BIOS)	?
$380065	?	?	Write only (used by the MVS BIOS)	?
$380067	?	?	Write only (used by the MVS BIOS)	?
$3A0001	REG_DISPENABL	?	Enable display	?
$3A0003	REG_SWPBIOS	?	Select the bios vector table	?
$3A0005	?	?	Write only (used by the MVS BIOS)	?
$3A0007	?	?	Write only (used by the MVS BIOS)	?
$3A000A	REG_BRDFIX	?	Select board fix rom	?
$3A000C	REG_SRAMLOCK	?	Lock the SRAM	?
$3A000E	REG_PALBANK1	?	Select the bank 1 of palette ram	?
$3A0011	REG_DISPDSABL	?	Disable display	?
$3A0013	REG_SWPROM	?	Select the game vector table	?
$3A0015	?	?	Write only (used by the MVS BIOS)	?
$3A0017	?	?	Write only (used by the MVS BIOS)	?
$3A0019	?	?	Write only (used by the MVS BIOS)	?
$3A001A	REG_CRTFIX	?	Select game fix rom	?
$3A001C	REG_SRAMUNLOCK	?	Unlock the SRAM	?
$3A001E	REG_PALBANK0	?	Select the bank 0 of palette ram	?

System registers

Handled by a 74HC259 adressable latch on cart systems. Byte writes only.

Address	Name	Write
$3A0001	REG_DISPENABL	Normal video output
$3A0011	REG_DISPDSABL	Darken video output
$3A0003	?	Use the BIOS vector table
$3A0013	REG_SWPROM	Use the cart's vector table
$3A0005	REG_CRDUNLOCK1	Enable writes to memory card (use REG_CRDUNLOCK2 too)
$3A0015	REG_CRDLOCK1	Disable writes to memory card
$3A0007	REG_CRDLOCK2	Disable writes to memory card
$3A0017	REG_CRDUNLOCK2	Enable writes to memory card (use REG_CRDUNLOCK1 too)
$3A0009	?	?
$3A0019	?	?
$3A000B	REG_BRDFIX	Use the embedded SFIX and SM1 ROM
$3A001B	REG_CRTFIX	Use the cart's S ROM and M ROM
$3A000D	REG_SRAMLOCK	Write-protects SRAM (MVS)
$3A001D	REG_SRAMULOCK	Unprotects SRAM (MVS)
$3A000F	REG_PALBANK1	Use palette bank 1
$3A001F	REG_PALBANK0	Use palette bank 0

Video registers

Handled by the GPUs.

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	REG_VRAMMOD	Word	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. See Display timing ? 1:50Hz 0:60Hz Auto animation counter	Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Def Auto animation speed (in frames) Raster interrupt mode Raster interrupt enable 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 registers

NEO-MGA / LC8953 / LC98000 ?

Address	Name	Size	Read	Write	Handled by
$FF0002	?	Word	?	NeoRaine load_files	?
$FF0004	?	Word	?	CDM3-2 BIOS writes 0,1,3,7	?
$FF000E	?	Byte	?	CDM3-2 BIOS writes $3F,$3C	?
$FF000F	?	Byte	?	CDM3-2 BIOS writes $20,$10,$08,$04	?
$FF0011	?	Byte	?	CDM3-2 BIOS writes $FE	?
$FF0017	?	Byte	CDM3-2 BIOS read/writes bit 0		?
$FF0061	?	Byte	?	Bit4: Run microcode ?	LC8953
$FF0064~$FF0070	?	(Long)words	?	Registers used by microcode (NeoRaine upload_param)
$FF007E~$FF008F	?	Words	?	Microcode (16x9bit instructions ?)
$FF0101	?	Byte	?	CDM3-2 BIOS writes low nibble	?
$FF0103	?	Byte	CDM3-2 BIOS: sequential read/writes		?
$FF0105	?	Byte	?	upload_type_w	?
$FF0108	?	Word	?	CDM3-2 BIOS writes $5555	?
$FF010C	?	Word	?	CDM3-2 BIOS writes $5555 and reads	?
$FF0111	REG_DISBLSPR	Byte	?	Disable/enable sprites	NEO-GRC/NEO-OFC
$FF0115	REG_DISBLFIX	Byte	?	Disable/enable fix layer
$FF0119	REG_ENVIDEO	Byte	?	Enable/disable video output
$FF011C	REG_CDCONFIG	Word	Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Def 1 0 CD lid switch Configuration jumpers ?	?	NEO-CDD board
$FF0121	REG_UPMAPSPR	Byte	?	Set upload zone to SPR DRAM	?
$FF0123	REG_UPMAPPCM			Set upload zone to PCM DRAM
$FF0127	REG_UPMAPZ80			Set upload zone to Z80 DRAM
$FF0129	REG_UPMAPFIX			Set upload zone to FIX DRAM
$FF0141	REG_UPUNMAPSPR			Unset SPR DRAM to upload zone
$FF0143	REG_UPUNMAPPCM			Unset PCM DRAM to upload zone
$FF0147	REG_UPUNMAPZ80			Unset Z80 DRAM to upload zone
$FF0149	REG_UPUNMAPFIX			Unset FIX DRAM to upload zone
$FF016F	REG_DISBLIRQ	Byte	?	Disable/enable interrupts	?
$FF0183	REG_ENZ80	Byte	?	Enable/disable(reset) Z80	?
$FF0188	REG_CDDALEFTL	Word	See Reading CDDA sound levels	?	NEO-MGA
$FF018A	REG_CDDARIGHTL
$FF01A1	?	Byte	?	Upload zone 1MiB SPR DRAM bank selection	?
$FF01A3	?	Byte	?	Upload zone 1MiB PCM DRAM bank selection	?
$FF01A7	?	Byte	?	CDM3-2 BIOS writes	?
$FF01FC	?	Word	?	CDDA control ?	?
$FF01FE	?	Word	?	CD DA/data switch ?	?