Extended NES I/O

The Extended NES I/O (ENIO) is a homebrew device by Chykn consisting of an EXP board and a CPU board. The EXP board plugs into the NES-001 expansion port and provides expansion audio and various headers, while the CPU board attaches to the EXP board and provides networking, storage, and USB. The EXP board was produced and sold in small quantities, while the CPU board did not make it beyond prototypes and was not sold. As such, much of this information has been sourced from archives of public documentation.

EXP board

The EXP board enables expansion audio by connecting EXP6 to the expansion port's audio in with a 47K resistor. Headers are included breaking out the various expansion port signals, one of them providing Famicom expansion port functionality via an included cable.

Pinout (v1.2)

J2: Famicom EXP Pin Compatible Header (16-pin R/A IDC)

                +------+
         GND -- |01  02| <- Audio In (not connected)
        /IRQ ?? |03  04| ?? Joypad 2 D4
 Joypad 2 D3 ?? |05  06| <- Joypad 2 D2
 Joypad 2 D1 -> |07  08  ?? Joypad 2 D0
Joypad 2 /OE <- |09  10  -> OUT2
        OUT1 <- |11  12| -> OUT0
 Joypad 1 D1 <- |13  14| -> Joypad 1 /OE
         +5V -- |15  16| -- NC
                +------+

Notes:
 - ?? directionality depends on the presence of other hardware, such as a joypad or a cartridge that always drives /IRQ. If conflicting hardware is not present, these can be used as inputs to the console.
 - J2.2 Audio In: On the Famicom, this pin is used for audio out, though can accept audio input. Here, it connects to J6.2 and is intended to connect to the NES audio in via a 47K resistor, but this resistor and header are both not populated, leaving this pin not connected.
 - The EXP board came with an adapter cable that connects to this header and provides a Famicom-compatible male DA15 port.

J3: ENIO CPU Board Header (26-pin R/A IDC)

                   +------+
            +5V -- |01  02| -- GND
            A15 <- |03  04| -> OUT2
           OUT1 <- |05  06| -> OUT0
           EXP9 ?? |07  08| ?? EXP8
           EXP7 ?? |09  10| ?? EXP5
   Joypad 2 /OE <- |11  12| ?? Joypad 2 D0
    Joypad 2 D1 -> |13  14  <- Joypad 2 D2
    Joypad 2 D3 ?? |15  16| ?? Joypad 2 D4
         CPU D0 <> |17  18| <> CPU D1
         CPU D2 <> |19  20| <> CPU D3
         CPU D4 <> |21  22| <> CPU D5
         CPU D6 <> |23  24| <> CPU D7
Unregulated Vdd -- |25  26| ?? /IRQ
                   +------+

Notes:
 - ?? directionality depends on the presence of other hardware, such as a joypad or a cartridge that always drives /IRQ. If conflicting hardware is not present, these can be used as inputs to the console.

J4: Misc Signal Header (16-pin unpopulated)

             +5V -- |01  02| -- GND
            EXP0 ?? |03  04| <> /NMI
            EXP2 ?? |05  06| ?? EXP1
            EXP4 ?? |07  08| ?? EXP3
     Joypad 1 D4 ?? |09  10| -> Joypad 1 /OE
     Joypad 1 D2 -> |11  12| ?? Joypad 1 D3
     Joypad 1 D0 ?? |13  14| -> Joypad 1 D1
4.00 MHz CIC CLK <- |15  16| ?? /IRQ

Notes:
 - ?? directionality depends on the presence of other hardware, such as a joypad or a cartridge that always drives /IRQ. If conflicting hardware is not present, these can be used as inputs to the console.

J5: Audio and Video Out (3-pin unpopulated)

|1| -- GND
|2| -> Audio Out
|3| -> Video Out

J6: Audio In (2-pin unpopulated)

|1| -- GND
|2| <- Audio In (not connected)

Notes:
 - J6.2 Audio In: Connects to J2.2, but does not connect to the console. See J2.2 above.

J7: NES EXP connector

See NES expansion port.

CPU board

The CPU board contains the following components:

• PIC32
• 100 Mb ethernet port
• MicroSD cart slot (for bootloading or game data storage)
• USB A port (such as for keyboards)
• MiniUSB port (for power if not connected to the console)
• 26-pin IDC header (see EXP board J3 above)
• Xilinx CPLD
• 3.3V switching regulator (selectable between 5V and unregulated Vdd, and 5V selectable between NES and miniUSB)

The CPLD enables communication between the NES and PIC, raising an interrupt on the PIC on access, and also acts as a level shifter. The PIC establishes network connections, transfers data, and buffers the CGP (Classic Gaming Protocol) packets sent between the ENIO and NES.

Addressing

The CPU board can be accessed 8 bits at a time in two ways.

Compatibility Mode

This can be used with any cartridge hardware, but is not compatible with a second controller. This uses:

• $4017R for reads
• Any address below $8000 for writes
• OUT1 as R/W

Direct Addressing Mode

This uses the cartridge to map reads and writes to $4700, supplying R/W and /CE to the CPU board via EXP pins.