Most names come from the official schematics.
Some help to decipher the names:
- / means the signal is active low.
- OE means Output Enable.
- U is used for Upper (even) byte.
- L is used for Lower (odd) byte.
- B as suffix often means the signal is inverted.
| Name
|
Description
|
Comes from
|
Fault consequence
|
| 24M
|
24MHz master clock
|
NEO-D0
|
Nothing works, no video at all
|
| 12M
|
12MHz clock (24/2) non-inverted
|
NEO-D0
|
Bad graphics
|
| 8M
|
8MHz clock (24/3) non-inverted
|
LSPC
|
No sound
|
| 6MB
|
6MHz clock (24/4) inverted
|
NEO-D0
|
Black screen ?
|
| 4M
|
4MHz clock (24/6) non-inverted
|
LSPC
|
No sound
|
| 4MB
|
4MHz clock (24/6) inverted
|
LSPC + inverter
|
?
|
| 1MB
|
3MHz (!) clock (24/8) inverted
|
NEO-D0
|
?
|
| 68KCLK
|
12MHz clock (24/2) non-inverted
|
NEO-D0
|
Click of death
|
| 68KCLKB
|
12MHz clock (24/2) inverted
|
NEO-D0
|
Bad audio in games using PCM
|
| 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 crashes, bad graphics
|
| /PORTOEL
|
$200000-$2FFFFF (P2 ROM/Security chip) odd byte read
|
Control
|
NEO-C1
|
Game crashes, bad graphics
|
| /PORTOEU
|
$200000-$2FFFFF (P2 ROM/Security chip) even byte read
|
Control
|
NEO-C1
|
Game crashes, bad graphics
|
| /PORTWEL
|
$200000-$2FFFFF (P2 ROM/Security chip) odd byte write
|
Control
|
NEO-C1
|
Game crashes, multiplayer comm. error
|
| /PORTWEU
|
$200000-$2FFFFF (P2 ROM/Security chip) even byte write
|
Control
|
NEO-C1
|
Game crashes, bad graphics
|
| /PWAIT0, /PWAIT1
|
Delay configuration for P2 ROM reads, see wait cycle
|
Control
|
NEO-C1
|
Game crashes (very likely)
|
| 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
|
| PAL
|
Palette RAM decode for 68k access
|
Control
|
NEO-C1
|
Bad colors, snow, black screen
|
| PCK1, PCK2
|
Graphics rendering control
|
Control
|
LSPC2-A2
|
Bad graphics, solid colors, black screen
|
| PCK1B, PCK2B
|
Graphics rendering control
|
Control
|
AS04 inverters
|
Bad graphics
|
- 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.
Misc.
- SYSTEM: low when onboard ROMs selected
- SYSTEMB: inverted SYSTEM
- SDA0~SDA15 : Z80 address bus
- SDD0~SDD7: Z80 data bus
Sound
- 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