If you are looking to link up for Saturn or Dreamcast for some local LAN head to head gaming you will find that your options for cabling will be a bit on the expensive side, to say the least. 3rd party products do exist, but they are unreliable and likely just as rare.
As a follow up to our multiplayer/LAN adventure, we have been doing some experimentation with SEGAs line of system link capable consoles. We have found that it is possible to make your own cable using a few of the more common types of modern connectors.
Make A SEGA Dreamcast VS Link Cable With An HDMI Cable
2 Dreamcasts can connect to each other via a serial connection. Keep in mind that this is different from the dial up/LAN adapter so this connection must be made using the Dreamcast’s modified serial port.
The serial port on the Dreamcast is an 10 pin connector, so its actually possible cut the top half Of an HDMI connector off, allowing it to be inserted almost perfectly into the serial port. You may have to do a bit of trimming on the right & left sides depending on your particular brand of HDMI cable, and the top half will need to have something glued onto it in order for there to be enough downward force to make good contact with the pins.
Here is a diagram for the wiring. Keep in mind you will have to cross RxD, TxD, RTS, and CTS (hopefully your HDMI cable has internal colored wires!) when you wire your connector.
3D Printed SEGA Saturn Link Cable
Although Saturn link cables are not quite as rare as the aforementioned Dreamcast varieties, they can still be quite expensive.
As luck would have it, a 3D printed option exists that is quite functional, if you are willing to source and connect some tiny Molex KK 2759 wires. The Saturn utilizes and unique double sided 8 pin connector and the tolerances are fairly low as far as dimensions are concerned, so you will need use a printer that is in decent shape and is capable of 0.1mm layer height and 0.19mm (although a 0.2mm nozzle is recommended) nozzle width.
Diy Saturn Link Cable
Making your own cables can be very labor intensive, and after chopping up 3 or 4 HDMI cables for friends I was more than ready for an alternative solution for my own personal use/testing.
If you’re not afraid of a little soldering, and don’t mind having a more permanent solution dangling off the back of your console, consider a JST connector. JST cables are common and can be bought in a male/female configuration, allowing for a much more secure cabling solution. You will of course have to solder up the corresponding pins on each console. The Saturn actually has test points for its Serial connector, which makes soldering in your cable very easy. I was able to figure out the pinout of the Saturn Serial connector with a little bit of probing.
If you wish to join 2 Saturns this way, make sure you cross the TX/RX lines when linking the second console.