Creating a ComLynx to USB cable

The Atari Lynx consoles can be connected together with a ComLynx cable. I have written about this before and showed how they can also be chain-linked to connect up to 16 consoles. The commercial games only had support for up to 8 (Todd’s Adventures in Slime World, the only one with 8).

But, in the nineties Bastian Schick already developed a ComLynx to RS232 cable that allowed you to connect your Lynx to a PC with a COM port.

cl_232

Since I am no hardware or electronics expert I decided to go a different route: create a ComLynx to USB myself. That would also solve the problem of requiring a computer that still has a COM port. I know mine doesn’t have one. There has been talk about building a ComLynx to USB cable in the AtariAge Lynx forums before. GadgetUK managed to build one, as you can see in the pictures there. He also wrote a .NET program Zeus (with sources) that works excellently and allowed me to test-drive the cable.

Getting started

The Lynx uses UART to let the consoles to talk to each other. There is a lot of material available on the Internet. You could even read a part of my tutorial that brings you up to speed on the Lynx and UART.

Let’s take a look at what a ComLynx cable looks like:

There are two male and one female connector. You can read more about this at a previous blog post. Inside the ComLynx cable there are two wires. I never ever opened a ComLynx cable up. So, in the interest of science I cut open the cable at the end that has the single male. The idea was that I could still use the other end to link to more than one Lynx. Here’s the inside of the cable:

WP_002196 (2)

The cable shows two wires only. After some reading and measuring I came to this conclusion:

  1. Red: Corresponds to the +5V that the ComLynx uses for the high signal of the UART and is the combined receive (RX) and transmit (TX) signals
  2. White: Ground cable (GND)

Alright, that part was easy. The next part is to find some piece of electronics that can be used to connect to the PC via USB.

USB to UART hardware

Searching through eBay I selected the following USB to UART pieces of electronics that seemed to fit the bill: the required connectors (GND, RX, TX and optionally +5V) and cheap (ranging from ($2,60 to $8,05).

  1. Silicon Labs CP2102 USB connectivity bridge (driver)
  2. Prolific PL2303HX  (driver)
  3. FTDI FT232RL USB to TTL serial cable adapter (driver)

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I took the pictures from eBay to show what they are like. The first one is very bare, and uses a 6-pin connector. The second from Prolific has a casing and cable with a loose end. It’s the casing that is most interesting. Finally, the FTDI version has some neat connector-thingies at the end for each of the six loose wires.

Now, a thing to note is that the Prolific one. It turned out that the chipset that is used in this connector is sometimes a fake Chinese one, not the original Prolific. The latest drivers from Prolific will detect and reject the chipset. The result is a Windows device that is detected, but lacking driver support.

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In the properties of the device error code 10 is shown.

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Apparently the older drivers did not have this fake chipset detection and worked OK. The older driver that was referenced in the eBay auction might help. Some more info I found here.

I do not know if mine is a fake one. There is also no support for Windows 8 for the HXA model, whether it is fake or genuine. I should have read the description better.

Installing USB drivers

The Silicon Labs and FTDI USB devices both installed pretty smoothly. Once inserted in your USB slot Windows will detect it and (attempt to) install its own drivers first.

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Windows is really helpful here and offers a link to the download location of the manufacturer.

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The Prolific device does not have an appropriate Windows driver as part of the OS installation.

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Windows 7/8 will find drivers for the FTDI one. However, these are not suitable. You will need to download the appropriate drivers from the manufacturer’s website. I’ve included the links to the drivers in the list above. Windows 8.1 has the drivers for FTDI out-of-the-box.

Running Windows 8 the registered FTDI device showed up as a FT232R, indicating that the driver is not available yet.

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After that I installed the Virtual Com Port (VCP) driver from FTDI and the Silicon Labs driver. The end result is two properly registered USB to UART devices.

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Building the physical wire

With the USB devices and driver troubles out of the way there is nothing holding us back in that respect. Let’s connect the ComLynx cable to the USB device.

I came up with two strategies:

  1. Connect/solder cable to the USB device
    Since I already opened a cable I might as well connect it to the USB device itself.
  2. Keep ComLynx cable and device intact
    This means that the cable will not be cut and the device will not require any cutting, soldering or whatever.

Soldering away

Going with number 1 first I looked at the back of the FTDI device after opening up the USB case. There I found that it neatly shows what each pin is used for.

TODO: New pictures

So, I soldered the red cable for combined RX and TX to the two pins that were indicated as RXD and TXD. The white ground wire connects to GND. The end result with the casing assembled again looks pretty swell.

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When I did the same for the Prolific device, I couldn’t test that wire with my Windows 8.1 machine, because of the aforementioned incompatibility of the Prolific chipset.

I had already used the Silicon Labs version and that turned out to work alright as well. The end result wasn’t as pretty as the previous one, so I took it apart again and build the one shown above. When I rebuild it using the Silicon Labs device I will post new pictures here.

Inside the ComLynx connector

Since the other strategy would not allow me to mutilate the original ComLynx cable or solder at the device, I had to sacrifice another thing: the ComLynx connector. Fortunately I have several of those lying around from all the broken Lynx boards I acquired over the years.

The next picture shows the loose connector’s back, front and inside.

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It may be kind of hard to see, but the back shows four pins:

  • Left side: a single pin that corresponds to RX and TX
  • Top side: again, a single pin for GND
  • Right side: two pins, of which I do not know the function (anyone care to comment?)

Here’s what the ComLynx cable looks like inserted into the connector.

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I used a simple solder board to align the top and left pin to two little connectors that can hold the individual wires of the FTDI device’s cable. The two pins at the right side (left facing the front) were bent outwards, so they wouldn’t connect or interfere with the rest.

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You can see how I soldered them to the board.

With that done I could finally insert the ComLynx cable into the connector. All that was left was to hook up the beautifully colored wires of the FTDI device to the little two connectors at the right of the ComLynx connector.

The color scheme for the FTDI cable (in my case) was like this:

Color Function
Black GND
Blue CTS
Red +5V
Green TXD
White RXD
Yellow RTS

That meant that the white and the green should be at the bottom row and the black cable at either one of the top pins.

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Well, maybe not as neat as the previous one, but you don’t have to ruin a perfectly fine ComLynx cable nor solder the original wire. I might leave this as is or take the USB device apart to go for strategy 1 with it. I think it is more practical to have a single cable, instead of two separate cables and an open electronic board.

Test driving the cables

Aah, yes, the testing. At this point you will have to wait for my tutorial series to catch up. I did the first part on ComLynx already. The next one will show how to program the Lynx for UART and will make extensive use of the cable.

Or, you can ask for me to do a write-up before that. Feel free to ask any questions. Good luck building your own cable.

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One Response to Creating a ComLynx to USB cable

  1. Johney says:

    Does someone knows were the white ground wire is used for?!
    I find it strange that the red wire is used for both sending & recieving signal unless,,,,, the sended signal is coded in a low freq and the recieved signal coded in a high freq sothat both signals never crashing & interrupt eachother,,,,, or it functions like a alternating traffic system to only allow 1 signal to get passtrough,(aka walki talki system??)

    If it turns out that other connected lynxes can only listen to the main lynx at all time, then it’s impossible to play head to head games such as tetris wich require a 2 way traffic system, in this you can split that signal as much you want from the main lynx sothat other users can see what you do but you cannot see them in your game,

    Because according to wiki uart is just an analogue systen with limited bandwidch just like an antenna, in this this case,,why did the lynx designers not just choose for a high bandwidch 2 traffic digital output, rather then a fency analogue crap.

    Anyway i see potential in that usb comlynx as you may could setup an online network to play multi player lynx games that way via both emulator and lynx systems.

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