Signals

Most names come from the official schematics.

Clocks

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

CPU (68k)

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

Graphics

Name	Description	Type	Comes from	Fault consequence
2H1	S ROM A3	Address	LSPC	Bad fix graphics
CA4	C ROMs A4	Address	LSPC	Bad sprite graphics
C* or CR0~CR31	C ROMs data bus (2*16bits), data for one 8-pixels line	Data	C ROM	Bad sprite graphics
FIXD0~FIXD7	Fix layer data bus, data for 2 pixels	Data	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	NEO-B1	Bad colors, snow, black screen

Misc.

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

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