EXP pins
The EXP pins are expansion pins present on the 72-pin NES cartridge connector and which connect to the expansion port on the bottom of the NES-001 console. These pins were not used by any officially released consumer device, but are used by various unlicensed devices and the FamicomBox hotel console.
Pin summary
| EXP0 | EXP1 | EXP2 | EXP3 | EXP4 | EXP5 | EXP6 | EXP7 | EXP8 | EXP9 | |
|---|---|---|---|---|---|---|---|---|---|---|
| CopyNES | ✓ | |||||||||
| Everdrive N8 | ♪ | |||||||||
| Everdrive N8 Pro | ~ | ~ | ~ | ~ | ~ | ~ | ♪ | ~ | ~ | ~ |
| Expansion Port Sound Module (EPSM) | ✓ | ✓ | ✓ | ♪ | ✓ | ✓ | ||||
| ExROM (MMC5) | ✓ | ♪ | ||||||||
| Extended NES I/O (ENIO) | ~ | ~ | ~ | ~ | ~ | ✓ | ♪ | ✓ | ✓ | ✓ |
| Famicom-to-NES adapter | ♪* | ♪* | ||||||||
| FamicomBox | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| INL expansion audio module | ♪ | |||||||||
| Muramasa NES FDS | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ♪ | ✓ | ✓ | ✓ |
| NES-21G-CPU-72P | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| PowerPak | ✓ | ~ | ~ | ~ | ~ | ~ | ♪ | ~ | ~ | |
| PowerPak Lite | ✓ | |||||||||
| TinyNES | ♪ |
✓ : This pin is used.
♪ : This pin is used for expansion audio output (cartridge) or input (expansion device or console).
* : This pin is used by some, but not all such devices.
~ : This pin is connected, but lacks a specific function.
Pin notes
EXP0
Some modern cartridges have been observed that connect EXP0 to ground, likely because of the presence of a ground pin on the Famicom's cartridge connector in the region where the EXP pins are placed on the NES'. This provides no meaningful benefit and adds risk. For example, inserting such a cartridge into the FamicomBox can short 5V to ground through this pin, causing damage to the cartridge or console.
EXP2
EXP2 is not present on the NES-101.
EXP3
EXP3 is not present on the NES-101.
EXP5
EXP5 is not present on the NES-101.
EXP6
EXP6 is not present on the NES-101. It has become the standard console input for expansion audio and is used by flash carts, modern homebrew, and modern Famicom-to-NES adapters.
EXP9
Because EXP6 is not present on the NES-101, some NES-101 users have modified cartridges to send expansion audio over EXP9, instead.
Devices
CopyNES
The CopyNES uses EXP0 to write to RAM carts, such as the PowerPak Lite.
Expansion Port Sound Module (EPSM)
The EPSM can be written through either a cart-agnostic universal access mode or a mapper-specific mode, where the cartridge decodes the address and passes chip enable and address bits via EXP pins. It also accepts expansion audio input on EXP6.
Expansion Port | Cart | Expansion Port
-----------------
...
YMF288 A1 <- |20 EXP4
EPSM /CE2 <- |19 EXP3 EXP5 55|
|18 EXP2 EXP6 54| -> audio
EPSM /CE1 <- |17 EXP1 EXP7 53| -> YMF288 A0
|16 EXP0 EXP8 52| -> EPSM CE3
EXP9 51|
...
ExROM (MMC5)
ExROM boards, using MMC5, are configured for expansion audio output on EXP6, though the boards must also have the appropriate resistors and capacitors populated for this to function. EXP5, which is pulled low in the cart, is used as a PRG-RAM read disable.
Expansion Port | Cart | Expansion Port
-----------------
...
|20 EXP4
|19 EXP3 EXP5 55| <- PRG-RAM /OE
|18 EXP2 EXP6 54| -> audio
|17 EXP1 EXP7 53|
|16 EXP0 EXP8 52|
EXP9 51|
...
Extended NES I/O (ENIO)
The ENIO CPU board can be accessed through either a cart-agnostic compatibility mode or a direct addressing mode, where the cartridge decodes the address and passes R/W and /CE to the ENIO via EXP pins. EXP5 and EXP7-9 are passed to the CPU board, handling R/W, /CE, and presumably other currently-undocumented functionality. EXP6 is used as an expansion audio input. EXP0-4 are routed to an unpopulated header for expansion use.
Expansion Port | Cart | Expansion Port
-----------------
...
ENIO J4 header ?? |20 EXP4
ENIO J4 header ?? |19 EXP3 EXP5 55| ?? unknown (ENIO CPU board)
ENIO J4 header ?? |18 EXP2 EXP6 54| -> audio
ENIO J4 header ?? |17 EXP1 EXP7 53| -> ENIO R/W
ENIO J4 header ?? |16 EXP0 EXP8 52| -> ENIO /CE
EXP9 51| ?? unknown (ENIO CPU board)
...
Famicom-to-NES adapter
Some Famicom-to-NES adapters connect expansion audio to an EXP pin. If connected, modern adapters typically use EXP6, though EXP2 has been observed due to its proximity to the audio-to-RF pin on the Famicom cartridge connector.
FamicomBox
The FamicomBox uses the EXP pins primarily to indicate slot ID to the cartridge's 3198 CIC. 9 of the pins are tied to some combination of ground and 5V, which can cause damage to non-FamicomBox cartridges that use EXP pins. One additional pin provides A15, which is not used by any contemporary game. Unlike the NES-001, the FamicomBox does not route any of these pins to any external port for expansion use.
FamicomBox | Cart | FamicomBox
-----------------
...
CPU A15 -> |20 EXP4
/SlotIndex3 -> |19 EXP3 EXP5 55| -- GND
/SlotIndex2 -> |18 EXP2 EXP6 54| -- GND
/SlotIndex1 -> |17 EXP1 EXP7 53| -- GND
/SlotIndex0 -> |16 EXP0 EXP8 52| -- +5V
EXP9 51| -- +5V
...
Muramasa NES FDS
Because the NES-001 doesn't easily allow a cartridge to connect with another device via an external cable, Muramasa's NES FDS connects the RAM adapter cartridge and disk drive via the EXP pins.
Expansion Port | Cart | Expansion Port
-----------------
...
serial out <- |20 EXP4
(R/W) $4034.W2 <- |19 EXP3 EXP5 55| <- serial in
(transfer reset) $4035.W1 <- |18 EXP2 EXP6 54| -> audio
(write protected) $4032.R2 -> |17 EXP1 EXP7 53| -> $4025.W0 (motor control)
(disk /ready) $4032.R1 -> |16 EXP0 EXP8 52| <- $4032.R0 (disk /inserted)
EXP9 51| <- battery
...
NES-21G-CPU-72P
The NES-21G-CPU-72P board is used in some Nintendo test cartridges and uses the EXP pins to interact with an unknown device. The last value written to $6000 is outputted over 8 EXP pins, with the high bit also signaling whether the M2 and the system clock inputs are not functioning. EXP6 indicates when $6000 is being read, and it is speculated that this would cause the expansion device to drive the latched data onto the CPU data lines. EXP5 is used, but its effect is currently unknown; it may control the PRG-ROM's /OE.
Expansion Port | Cart | Expansion Port
-----------------
...
$6000.R4 <- |20 EXP4
$6000.R3 <- |19 EXP3 EXP5 55| <- unknown
$6000.R2 <- |18 EXP2 EXP6 54| -> $6000 /read
$6000.R1 <- |17 EXP1 EXP7 53| -> $6000.R7 OR clocks bad
$6000.R0 <- |16 EXP0 EXP8 52| -> $6000.R6
EXP9 51| -> $6000.R5
...
NES modem
The NES modem is an unreleased official expansion device that would have allowed online access. It is highly likely this device uses the EXP pins, but no specifics are known.
PowerPak
The PowerPak uses EXP0 to allow the CopyNES to program the boot ROM. EXP1-8 are connected to the FPGA and can be used, but only EXP6 has been (for expansion audio output). EXP9 is not connected, and some users have bridged it with EXP6 to enable expansion audio on NES-101 consoles.
Expansion Port | Cart | Expansion Port
-----------------
...
FPGA pin 22 ?? |20 EXP4
FPGA pin 20 ?? |19 EXP3 EXP5 55| ?? FPGA pin 19
FPGA pin 27 ?? |18 EXP2 EXP6 54| -> audio (FPGA pin 23)
FPGA pin 12 ?? |17 EXP1 EXP7 53| ?? FPGA pin 94
boot ROM program -> |16 EXP0 EXP8 52| ?? FPGA pin 41
EXP9 51|
...
PowerPak Lite
The PowerPak Lite is programmed with settings for the current game by a CopyNES via EXP0.
