Connecting your rosco_m68k

Once you've built your new old computer, it's time to start talking to it!

Hooking up your rosco_m68k to your regular modern computer is a simple affair, thanks to the wonders of modern technolgy. USB to Serial (i.e. UART) converters are cheap and plentiful, and you might even have received one along with your kit (if you opted for one when you purchased). Let's look at what you'll need to get started.

In this section, you'll need:

  • A USB lead with +5V and GND broken out to Dupont® connectors, or alternative power connector
  • A USB to Serial converter (sometimes called an FTDI converter) or cable
  • A USB Mini-B to A cable

Connecting the power

You'll need some kind of 5V power supply that can connect to the two-pin power header on the rosco_m68k. We use modified USB cables and regular wall-wart adapters for this, but any well-regulated 5V power source will work just fine. 

If you don't have a power lead, it's easy to make one from an old USB lead - check out this video, for example.

When connecting the power, be sure to observe the polarity - the pins are clearly marked on the board as 5VDC and GND. If using a USB cable, these should be connected to the red and black wires, respectively. It's really important to connect these correctly, getting them the wrong way round will damage your rosco_m68k! If in doubt, use a multimeter to check the polarity before you connect.

Connecting the UART to the USB to Serial converter

The exact method for doing this will vary depending on the specific converter you have, but the general principle remains the same. 

Find the four-pin UART connector on your rosco_m68k - it's on the right side of the board, and the pins are marked CTSRXDTXD and GND. 

Now, on your USB to Serial converter, find the corresponding four pins. Most converters (including the one we optionally supply) will already have headers soldered on for these pins.

Using a four-way wire with DuPont connectors at each end, make the following connections:

rosco_m68k UART PinUSB to Serial Converter Pin
RXDTXD (Sometimes labeled TX)
TXDRXD (Sometimes labeled RX)

Now connect the USB cable from your USB to Serial converter to your computer. The converter will probably have some LEDs that light up at this point, and your computer should recognise it as a new serial device.

The new device should appear in the /dev directory, ready for use. On my Mac, for example, it's named /dev/cu.usbserial-A50285BI and /dev/tty.usbserial-A50285BI. The name will vary depending on your device, and you'll need to know it in the next step. On Mac, you can find it easily by looking at the output of this command:

ls /dev/cu*

In the output of this you should see something like /dev/cu.usbserial-XXXX - this will be your device (if you have multiple USB Serial devices connected, you may need to look at the output before and after connecting to determine which is the correct one. You can also view this information in the GUI but how this is done varies based on the macOS® version you're running). 

On Linux, you can find the name of the device by looking at the output of the 'dmesg' command.

Connecting an SD Card

If you're running Firmware v1.3 and up, you can connect an SD card using an Arduino SD card adapter. Depending on your board revision, this either connects to a dedicated header (on 1.23 boards and higher) or to J5 (on 1.2 boards and below). 

See this page for detailed hookup guide, as well as information on supported cards and formatting.

Installing Software and Testing

In this section we'll install two programs, minicom and ckermit. If you already have them installed, or have another terminal emulator / kermit client that you like, then feel free to skip this section.

We recommend using Homebrew to manage your software. If you already did the Toolchain Installation, then the chances are you already installed Homebrew. We'll document the steps needed with Homebrew here. If you don't already have it, you can find simple installation instructions at

If you're using Linux and don't want to install Homebrew, it's very likely that both these packages are available from your distribution's standard package repositories - you'll be able to install them with apt-get, yum, dnf, or whatever your regular package manager is called.

Run the following to install the two packages we need:

brew install minicom c-kermit

(Note that, if using your Linux distribution's package manager, the Kermit package is likely to be called 'ckermit' instead of 'c-kermit').

After a short installation, both packages should be ready to use, but we need to add a little bit of configuration first.

Create a new file in your home directory called  .kermrc, or edit the existing if it already exists. Notice the leading period! The contents of this file should be

set carrier-watch off ;
set flow xon/xoff ;

Briefly, this disables the carrier detect line (you could also short this line to ground on your USB to Serial converter if you wished, but it's easier to configure it here), tells Kermit to use XON/XOFF flow control (also known as Software flow control), and sets the robust transfer mode. Robust mode is quite slow, but is the only mode supported by the rosco_m68k firmware at the moment.

Now launch minicom:

minicom -D /dev/cu.usbserial-XXXX -c on -R utf-8

Replace the /dev/cu.usbserial-XXXX with the path to the device you determined in the previous step. On Linux, this will probably start with /dev/tty... rather than /dev/cu...

Once Minicom has launched, we just need to configure it. 

Hit Esc+O (CTRL-A, O on Linux) to open the options, and navigate to Serial Port Setup'. You'll want to edit the options so they look something like the following image: 

(To configure a given option, hit the key in the left column).

We want to leave the A, B, C and D options as they are, but change E, F and G to match those shown above.

Once the options are set, ESCape out of the serial menu, and select "Save setup as dfl". This will show a message that the configuration has been saved, and you can now exit out of the menus altogether.

It's probably worth restarting minicom at this point - Esc+Q (Ctrl-A, Q on Linux) to quit then re-run the minicom command. All should now be ready - power up your rosco_m68k (or hit the reset button if it's already powered up), and you should see the following on-screen:

Congratulations - you're now all set, and your rosco_m68k can talk to your computer.

From here, you can use Esc+S (Ctrl-A, S on Linux) to initiate a Kermit file transfer, and send a compiled binary program to your board and interact with it in the serial terminal.

Now that the rosco_m68k is successfully talking to your computer, it's time to run some example programs! We'll do that in the next section.