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Package QFP100R
First use 1992 ?
Used on NEO-AES3-4 board...

Multi-purpose keystone chip used for address decoding, inter-CPU communications, wait cycle generation, and player inputs.

Maps itself to even byte access only (only D15~8 connected).


Edit this pinout




  • IN00: Up P1
  • IN01: Down P1
  • IN02: Left P1
  • IN03: Right P1
  • IN04: A P1
  • IN05: B P1
  • IN06: C P1
  • IN07: D P1


  • IN10: Up P2
  • IN11: Down P2
  • IN12: Left P2
  • IN13: Right P2
  • IN14: A P2
  • IN15: B P2
  • IN16: C P2
  • IN17: D P2


  • IN20: Start P1
  • IN21: Select P1
  • IN22: Start P2
  • IN23: Select P2
  • IN24: Memory card inserted
  • IN25: Memory card inserted
  • IN26: Memory card write protect
  • IN27: System type (home/arcade)


  • A17~A21: 68k address bus
  • A22I~A23I: NEO-E0 address input
  • D8~D15: 68k data bus
  • R/W,UDS,LDS,AS,DTACK: 68k bus control signals
  • 68KCLK: 12MHz 68k clock
  • ROMWAIT,PWAIT0,PWAIT1,PDTACK: signals from cart PROG board to configure how /DTACK is generated for ROMOE region (how is it configured?)

Decoded signals

The following output and write enables have an upper(U)/lower(L) byte enable signal based on /UDS and /LDS from the 68k.

  • ROMOEU,ROMOEL: $000000-$0FFFFF read, 68k program ROM on cart PROG board
  • WRU,WRL,WWU,WWL: $100000-$1FFFFF read/write, 68k user RAM
  • PORTOEU,PORTOEL,PORTWEU,PORTWEL: $200000-$2FFFFF read/write, multipurpose signal on cart PROG board
  • SRAMOEU,SRAMOEL,SRAMWEU,SRAMWEL: $D00000-$DFFFFF read/write, battery-backed RAM

On NEO-C1, when A23I A22I A21 A20 = 1100 and RW = 1, either SROMOEU and SROMOEL should be low depending on UDS and LDS

The following are expected to be word accessed, byte writes and reads are ignored or do not work as expected.

  • CRDO,CRDW: $800000-$BFFFFF read/write, memory card
  • CRDC: Memory card select (CRDO AND CRDW ?)
  • LSPOE,LSPWE: $3C0000-$3DFFFF read/write, LSPC2-A2
  • PAL: $400000-$7FFFFF access, enables transcievers attached to palette RAM for 68k access

Z80 I/O

  • SDD0~SDD7: Z80 data bus used for 68k/Z80 communication
  • SDZ80R,SDZ80W: read / write signals for Z80 communication
  • SDW: signals that 68k has written a byte to Z80 port, will make NEO-D0 generate interrupt if enabled
  • SDZ80CLR: initialise stored byte to zero?