Signals

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Most names come from the official schematics.

Clocks

Name Description Type Comes from Fault consequence
24M 24MHz master clock Clock Chipicon.png NEO-D0 Nothing works, no video at all
12M 12MHz clock (24/2) non-inverted Clock Chipicon.png NEO-D0 Bad graphics
8M 8MHz clock (24/3) non-inverted Clock Chipicon.png LSPC No sound
6MB 6MHz clock (24/4) inverted Clock Chipicon.png NEO-D0 Black screen ?
4M 4MHz clock (24/6) non-inverted Clock Chipicon.png LSPC No sound
4MB 4MHz clock (24/6) inverted Clock Chipicon.png LSPC + inverter ?
1MB 3MHz (!) clock (24/8) inverted Clock Chipicon.png NEO-D0 ?
68KCLK 12MHz clock (24/2) non-inverted Clock Chipicon.png NEO-D0 Click of death
68KCLKB 12MHz clock (24/2) inverted Clock Chipicon.png NEO-D0 Bad ADPCM-B instruments in games using Chipicon.png PCM

CPU (68k)

Name Description Type Comes from Fault consequence
A1~A23 68k address bus Address Chipicon.png 68k Click of death
A22I,A23I Altered address lines for 68k vector table swap Address Chipicon.png NEO-E0 Probably click of death
/AS 68k Address Strobe Control Chipicon.png 68k Probably click of death
D0~D15 68k data bus Data Multiple Click of death
/DTACK 68k Data Transmit ACKnowledge (see wait cycle) Control Chipicon.png NEO-C1 Click of death ?
/PORTADRS $200000-$2FFFFF (P2 ROM/Security chip) any access Control Chipicon.png NEO-C1 Game freezes, bad graphics
/PORTOEL $200000-$2FFFFF (P2 ROM/Security chip) odd byte read Control Chipicon.png NEO-C1 Game freezes, bad graphics
/PORTOEU $200000-$2FFFFF (P2 ROM/Security chip) even byte read Control Chipicon.png NEO-C1 Game freezes, bad graphics
/PORTWEL $200000-$2FFFFF (P2 ROM/Security chip) odd byte write Control Chipicon.png NEO-C1 Game freezes, multiplayer comm. error
/PORTWEU $200000-$2FFFFF (P2 ROM/Security chip) even byte write Control Chipicon.png NEO-C1 Game freezes, bad graphics
/PWAIT0, /PWAIT1 Adds 0 to 3 cycle delay for P2 ROM reads, see wait cycle Control Chipicon.png NEO-C1 Game freezes (unlikely)
R/W 68k Read/Write Control Chipicon.png 68k Click of death
/ROMOE $000000-$0FFFFF (P1 ROM) read Control Chipicon.png NEO-C1 + AND Game doesn't start
/ROMOEL $000000-$0FFFFF (P1 ROM) odd byte read Control Chipicon.png NEO-C1 Game doesn't start
/ROMOEU $000000-$0FFFFF (P1 ROM) even byte read Control Chipicon.png NEO-C1 Game doesn't start
/ROMWAIT Add 1-cycle delay for P1 ROM reads Control Chipicon.png NEO-C1 Game freezes (unlikely)
/SROMOE $C00000-$CFFFFF (System ROM) read Control Chipicon.png NEO-E0 Click of death
/SROMOEL $C00000-$CFFFFF (System ROM) odd byte read Control Chipicon.png NEO-C1 Click of death
/SROMOEU $C00000-$CFFFFF (System ROM) even byte read Control Chipicon.png NEO-C1 Click of death

Graphics

Name Description Type Comes from Fault consequence
2H1 S ROM A3 Address Chipicon.png LSPC Bad fix graphics
CA4 C ROMs A4 Address Chipicon.png LSPC Bad sprite graphics
C* or CR0~CR31 C ROMs data bus (2*16bits), data for one 8-pixels line Data Chipicon.png C ROM Bad sprite graphics
FIXD0~FIXD7 Fix layer data bus, data for 2 pixels Data Chipicon.png S ROM Static vertical lines, solid color screen
P0~P23 Multiplexed P bus Muxed Multiple Garbled or absent graphics
PA0~PA11 Palette RAM address bus Address Chipicon.png NEO-B1 Bad colors, snow, black screen

Misc.

Name Description Type Comes from Fault consequence
BNK0~2 Memory card bank selection Control Chipicon.png NEO-D0 Errors on access to big memory cards

CPU (Z80)

Sound

  • PAL: Palette RAM address decode for 68k access
  • PCK1B: Low 55ns, high 610 (1.5MHz) Clock to latch C ROM address from P0~P23 (mapping) on rising edge.
  • PCK2B: Low 55ns, high 610 (1.5MHz) Clock to latch S ROM address from P0~P15 (mapping) on rising edge.
  • SDA0~SDA15 : Z80 address bus
  • SDD0~SDD7: Z80 data bus
  • SDRAD0~SDRAD7: ADPCM-A ROM multiplexed bus (data/address)
  • SDRA8,SDRA9,SDRA20~SDRA23: ADPCM-A ROM address bus
  • SDPAD0~SDPAD7: ADPCM-B ROM multiplexed bus (data/address)
  • SDPA8,SDPA9,SDPA10,SDPA11: ADPCM-B ROM address bus
  • SYSTEM: low when onboard ROMs selected
  • SYSTEMB: inverted SYSTEM