Gcvideo lite

GCVideo Lite 0.9

This is the first prototype GCVideo Lite board with analog outputs in RGB and Component/YPbPr formats, revision 0.9. This revision has a few minor annoyances, but has proven to work.

Connectors

The board has five connectors and one jumper: The main signal and power input is the 11x2 connector P1 which connects to the GameCube Digital Video port. The 6x1 connector on the side is the JTAG connector which is needed to program the FPGA on the board. Signal outputs are on the 5x1 and 4x1 connectors. There is also a 2x2 connector labelled "spare" next to the P1 and JTAG connectors which at this time is mostly unused except for one pin that outputs an SPDIF audio signal.

The single jumper on the board is located next to the JTAG connector and consists of two solder pads. If these pads are bridged, the FPGA will output RGB signals, if they are open it will output component signals.

P1 (11x2)

The board is connected to the GameCube's digital video port using the pins of the P1 connector. Since the original connector in the GameCube is proprietary and no alternative is known, this needs to be done using wires. It is strongly recommended to keep these wires as short as possible since one of them is a 54MHz clock signal. Be absolutely sure to not connect or bridge anything to pin 5 (+12V) - an accidental short between that pin and any of the data lines will instantly fry the Gamecube.

The pins of the P1 connector on the GCVideo Lite board correspond 1:1 with the pins of the GC's digital video connector, pin 1 is marked with a square instead of a round pad. This site shows the pin numbering directly on the connector. Alternatively, if you look at the bottom of the GameCube's main PCB with the video connectors facing away from you, pin 1 of the DV connector should be the bottom right pin, pin 2 the one above it. There are also numbers for the outermost pins marked besides the connector on the top side.

I have no idea what your options are if you have a later-model GameCube where Nintendo removed the digital AV port.

JTAG (6x1)

The FPGA has an internal configuration memory which is blank when it is delivered from the factory. To program the FPGA, you need a JTAG interface suitable for use with Lattice's software - I use a clone of the HW-USBN-2A cable, but the software also supports a parallel port cable (no idea about the pinout) or FT2232D-based USB devices (look for Lattice application note AN8082 for the schematic).

On the software side, the FPGA can be programmed using the Lattice Diamond software package. Although it may appear a bit large at about 1.5 GByte download size, this is quite small compared to similar packages from other FPGA vendors. ;) If programming the internal configuration flash of the XO2 fails, try the .jed file instead of the .bit file.

Video (5x1)

The video output connector is the 5x1 connector on the side of the board. Pin 1 is marked using a square instead of a round pad and outputs the R (RGB) or Pr (Component, red plug) signal. Pins 2 and 4 are ground pins. Pin 3 (the middle one) outputs the G (RGB) or Y (Component, green plug) signal, Pin 5 outputs the B (RGB) or Pb (Component, blue plug) signal. There is also a tiny label hidden between the resistors and capacitors saying "B-G-R" which uses "-" as a shorthand for ground.

Sync (4x1)

The GCVideo Lite board has a dedicated connector for sync signals. You can ignore it if you only want to output Component video, but it is required if you want to use RGB. The pins are labelled "C V H -" on the sikscreen. The "-" pin is ground, "V" and "H" are vertical and horizontal sync signals and "C" is a composite sync signal. The composite sync signal should be directly usable e.g. for connections to SCART televisions or scalers like an XRGB Mini that need a composite sync while the V- and H-Sync signals can be used for VGA inputs - but remember that the GameCube outputs 15kHz video during startup and not every game supports 480p!

While the hardware could support RGB with Sync-on-Green, this is currently not implemented.

Spare (2x2)

The 2x2 pin group marked "Spare" in the corner of the group is unused except for the square pin next to P1. This pin is used to output an SPDIF audio signal. For more information on interfacing this signal to an SPDIF receiver, please check the README.md of the gcvideo_lite HDL project.

Please do not connect this pin directly to a coaxial SPDIF input, the feature was added after the board was designed and there is no protection on this pin.

Building

The PCB uses four layers, so it is not suitable for etching at home, but there are many prototyping services available that offer small runs of a PCB. The prototype has been ordered from OSHPark and the zip file with the data they require has been included in the repository.

The values of the parts are marked within their footprint in rather tiny letters, alternatively you can look at the BOM.csv file for the value corresponding to each of the component references.

Audio

There are currently two options for the audio signal from the Gamecube when GCVideo Lite is used as the video encoder. The first option is to use the audio signals from the analog AV port as usual. The second option is to use the SPDIF encoder implemented in GCVideo Lite. The README.md of the gcvideo_lite HDL project has more information about connecting this signal - since it was added after the board was designed, no protection is present on the signal and a direct connection to an SPDIF input may destroy the FPGA.

Known issues

• The drill holes for the JTAG and output video/sync connectors are slightly too small to fit standard 2.54mm pitch pin headers.
• The pads of the two ICs (from KiCADs standard footprint library) are meant for reflow soldering, not hand soldering. It is still possdo not need to use ible to hand-solder these chips, but it takes a lot of patience.
• The "component cable connected" pin is always active, which causes some homebrew applications to switch into 480p mode by default. This can be problematic for users of SD-only monitors, but since the board must be connected to the cube using wires anyway, leaving out the connection of pin 1 (or adding a switch in that line) can fix this issue.
• Trace width could be increased for some of the supply traces on the top and bottom layers.
• Vias are a bit large-ish.

Other Systems

With a different program in the FPGA it is be possible to use the same board to provide RGB and/or Component outputs for an N64, see the gcvideo_lite_n64 directory for details.

Measurements on a Wii board indicate that thare is an internal video data bus that may use the same signals as the GameCube's digital video port, but since the Wii already supports Component video natively there isn't much reason to actually use this board on a Wii. It may need some hardware changes as the Wii uses 1.8V signal levels instead of the 3.3V seen on a GameCube.