Memory mapped registers

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I/O registers

Always read/written as bytes (?)

Address Name Read Write Handled by
$300000 REG_P1CNT Player 1 controls or trackball data (active low)
Bit 7 6 5 4 3 2 1 0
Def D CBARightLeftDownUp
? NEO-C1
$300001 REG_DIPSW Hardware DIPs (active low)
Bit 7 6 5 4 3 2 1 0
Def Freeze FreeplayEnable Multiplayer configurationCommunication identification code0:Normal controller
1:Mahjong keyboard
0:One coin chute
1:Two coin chutes
Settings mode
Kick watchdog NEO-F0 (read)
$300081 ? IN01 to D7 (test switch) and TYPE to D6, see NEO-F0 ? NEO-F0
$320000 REG_SOUND Read Z80 reply code Send command to Z80 NEO-C1
$320001 REG_STATUS_A Switch inputs are active low
Bit 7 6 5 4 3 2 1 0
Def NEC D4990 data bit NEC D4990 time pulse0 on 4SLOT 1 on 6SLOT1 on 1FZServiceCoin 2Coin 1
? NEO-F0
$340000 REG_P2CNT Player 2 controls (active low)
Bit 7 6 5 4 3 2 1 0
Def D CBARightLeftDownUp
? NEO-C1
$380000 REG_STATUS_B Aux inputs (active low)
Bit 7 6 5 4 3 2 1 0
Def 0:AES
1:MVS
Memory card
write protected
Memory card
inserted if 00
Select P2Start P2Select P1Start P1
? NEO-C1
$380001 REG_POUTPUT ? Joypad ports outputs
Bit 7 6 5 4 3 2 1 0
Def ? P2 outputsP1 outputs

MAME select_controller

NEO-D0
$380011 REG_CRDBANK ?
Bit 7 6 5 4 3 2 1 0
Def Memory card bank selection
NEO-D0
$380021 REG_SLOT ?
Bit 7 6 5 4 3 2 1 0
Def ? Slot #

(On home systems this address is a mirror of REG_POUTPUT)

NEO-F0
$380031 REG_LEDLATCHES ? MAME set_output_latch
Bit 7 6 5 4 3 2 1 0
Def ? Latch LED2 dataLatch LED1 dataLatch EL panel data?

Data is latched on falling edge (1 to 0 transition)

NEO-F0
$380041 REG_LEDDATA ? MAME set_output_data (for LEDs and EL panel) NEO-F0
$380051 REG_RTCCTRL ? MAME upd4990a_control_16_w (Calendar)
Bit 7 6 5 4 3 2 1 0
Def D4990 StrobeD4990 ClockD4990 DIN
NEO-F0?
$380061 ? Chute 1 coin lockout -> High NEO-I0
$380063 ? Chute 2 coin lockout -> High NEO-I0
$380065 ? Chute 1 coin counter -> High NEO-I0
$380067 ? Chute 2 coin counter -> High NEO-I0
$3800D1 ? Write to RTC

uPD4990AWrite(byteValue & 2, byteValue & 4, byteValue & 1);

?
$3800E1 ? ? Chute 1 coin lockout -> Low NEO-I0
$3800E3 ? ? Chute 2 coin lockout -> Low NEO-I0
$3800E5 ? ? Chute 1 coin counter -> Low NEO-I0
$3800E7 ? ? Chute 2 coin counter -> Low NEO-I0

System registers

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

Address Name Write
$3A0001 REG_NOSHADOW Normal video output
$3A0011 REG_SHADOW Darken video output
$3A0003 REG_SWPBIOS 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 REG_CRDREGSEL Enable "Register select" for memory card
$3A0019 REG_CRDNORMAL Disable "Register select" for memory card
$3A000B REG_BRDFIX Use the embedded SFIX and SM1 ROM
$3A001B REG_CRTFIX Use the cart's S ROM and M1 ROM
$3A000D REG_SRAMLOCK Write-protects backup RAM (MVS)
$3A001D REG_SRAMULOCK Unprotects backup RAM (MVS)
$3A000F REG_PALBANK1 Use palette bank 1
$3A001F REG_PALBANK0 Use palette bank 0


Video registers

Handled by the GPUs. Byte writes only work on odd addresses and store the same data in the MSB and LSB.

Address Name Read Write
$3C0000 REG_VRAMADDR Read VRAM (address isn't changed) Sets VRAM address
$3C0002 REG_VRAMRW Read VRAM (address isn't changed) Write VRAM
$3C0004 REG_VRAMMOD Reads VRAM address modulo Sets VRAM address modulo (signed)
$3C0006 REG_LSPCMODE
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 (LSPC2 only)
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)
Timer interrupt
mode
Timer interrupt enableDisable auto animation?
$3C0008 REG_TIMERHIGH Invalid MSBs of timer reload value.
$3C000A REG_TIMERLOW Invalid LSBs of timer reload value.
$3C000C REG_IRQACK Invalid Interrupt Acknowledge (byte !).
Bit 7 6 5 4 3 2 1 0
Def ? Ack VBlankAck HBlankAck IRQ3
$3C000E REG_TIMERSTOP Invalid Bit 0=1: Stop timer counter for 32 raster lines when in PAL mode


NeoGeo CD registers

NEO-MGA / LC8953 / LC98000 ?

Address Name Size Read Write Handled by
$FF0002 ? Word ? NeoRaine load_files, really interrupt mask ? ?
$FF0004 ? Word ? CDM3-2 BIOS writes 0,1,3,7 ?
$FF000E ? Byte ? CDM3-2 BIOS writes $3F,$3C ?
$FF000F ? Byte ? NeoCDIRQUpdate(byteValue);

CDM3-2 BIOS writes $20,$10,$08,$04

?
$FF0011 ? Byte ? CDM3-2 BIOS writes $FE ?
$FF0017 ? Byte nNeoCDMode

CDM3-2 BIOS read/writes bit 0

?
$FF0061 ? Byte ? Bit 6: Execute DMA microcode LC8953
$FF0064~$FF0073 ? (Long)words ? Registers used by microcode (NeoRaine upload_param)
$FF007E~$FF008F ? Words ? Microcode (16x9bit instructions ?)
$FF0101 ? Byte nLC8951Register (4 LSB)

CDM3-2 BIOS writes low nibble

LC8951
$FF0103 ? Byte nLC8951Register value LC8951
$FF0105 ? Byte ? nActiveTransferArea = byteValue

upload_type_w

?
$FF0108 ? Word ? CDM3-2 BIOS writes $5555 ?
$FF010C ? Word ? CDM3-2 BIOS writes $5555 and reads ?
$FF0111 REG_DISBLSPR Byte ? 1=Disable 0=Enable sprites NEO-GRC/NEO-OFC
$FF0115 REG_DISBLFIX Byte ? 1=Disable 0=Enable fix layer
$FF0119 REG_ENVIDEO Byte ? Video output. 1=Enable 0=Disable (disable works for sure)
$FF011C REG_CDCONFIG Word
Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Def 1 0CD lid switchConfiguration jumpers?
? NEO-CDD board
$FF0121 REG_UPMAPSPR Byte ? NeoSetSpriteSlot(1);

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
$FF0161 ? ? ? NeoCDCommsRead Status FIFO 10 values (4 bits) ?
$FF0163 ? ? ? NeoCDCommsWrite(byteValue) Command FIFO 10 values (4 bits) ?
$FF0165 ? ? ? NeoCDCommsControl(byteValue & 1, byteValue & 2); (clock,send) ?
$FF016D Byte ? MapVectorTable(!(byteValue == 0xFF)); ?
$FF016F REG_DISBLIRQ Byte ? Disable/enable interrupts nTransferWriteEnable = byteValue ?
$FF0181 Byte ? Enable/Disable (Reset) CD assy ?
$FF0183 REG_ENZ80 Byte ? Enable/Disable (Reset) Z80 ?
$FF0188 REG_CDDALEFTL Word See Reading CDDA sound levels No effect NEO-MGA
$FF018A REG_CDDARIGHTL
$FF01A1 ? Byte ? Upload zone 1MiB SPR DRAM bank selection ?
$FF01A3 ? Byte ? Upload zone 512KiB PCM DRAM bank selection ?
$FF01A7 ? Byte ? CDM3-2 BIOS writes ?
$FF01FC ? Word ? CDDA control ? ?
$FF01FE ? Word ? CD DA/data switch ? ?