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 Autofire ? 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 ?	?	?
$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)	?

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	Allow /WE to pass through to memory card when low
$3A0015	REG_CRDLOCK1	Don't allow /WE to pass through to memory card
$3A0007	REG_CRDLOCK2	Don't allow /WE to pass through to memory card
$3A0017	REG_CRDUNLOCK1	Allow /WE to pass through to memory card when high
$3A0009	?	?
$3A0019	?	?
$3A000B	REG_BRDFIX	Use the embeded fix tileset (SFIX)
$3A001B	REG_CRTFIX	Use the cart's fix tileset
$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	?	Byte	?	spr_disable	?
$FF0115	?	Byte	?	fix_disable	?
$FF0119	?	Byte	?	video_enable	?
$FF011C	?	Word	4 bit region_code + CD open/close ?, 0xFF	?	?
$FF0121	REG_UPSELSPR	Byte		0/1 Map SPR in $E00000 ?	?
$FF0123	REG_UPSELPCM			0/1 Map PCM in $E00000 ?
$FF0127	REG_UPSELZ80			0/1 Map Z80 in $E00000 ?
$FF0129	REG_UPSELFIX			0/1 Map FIX in $E00000 ?
$FF0141	REG_UPUNMAPSPR			0/1 Unmap SPR in $E00000 ?
$FF0143	REG_UPUNMAPPCM			0/1 Unmap PCM in $E00000 ?
$FF0147	REG_UPUNMAPZ80			0/1 Unmap Z80 in $E00000 ?
$FF0149	REG_UPUNMAPFIX			0/1 Unmap FIX in $E00000 ?
$FF016F	?	Byte	?	disable_irq_w	?
$FF0183	?	Byte	?	z80_enable	?
$FF0188	REG_CDDALEFTL	Word	See Reading CDDA sound levels	?	NEO-MGA
$FF018A	REG_CDDARIGHTL			?
$FF01A1	?	Byte	?	CDM3-2 BIOS writes 0,1,2	?
$FF01A3	?	Byte	?	CDM3-2 BIOS writes 0,1	?
$FF01A7	?	Byte	?	CDM3-2 BIOS writes	?