Apple stopped putting serial ports on Macs in the late 1990’s. For the most part, I don’t miss them. In fact, I think every laptop I’ve been issued by an employer has been equipped with one of these dust gathering and finger scratching ports, and I would be happier without them. So, I can’t say I’m surprised to learn that the smooth and tidy back of my iMac does not have a serial port. Unfortunately, I have a few simple or old devices that still speak “serial”.

When I was working on my ECE degree, I purchased a USB-to-Serial adapter to connect my iBook to everything from oscilloscopes to micro-controllers. Earlier this week I had to dig out my adapter, a Keyspan USA-19, to update my DSL router (a story for another day).

As it turns out, Keyspan was bought by Tripp Lite in 2008, but appears to continue making and supporting Keyspan’s USB-to-Serial adpaters. I couldn’t find drivers for the USA-19, but took the risk an used the driver for the USA-19HS (Mac OS X 10.6.x to 10.8.x). There isn’t anything fancy about the installer; just follow the prompts.

Once the driver is installed, plug in the adapter and check for it with:

% ls -1 /dev/tty.*

I had to restart before I saw what I was looking for (I’ve omitted the results that aren’t relevant):

% ls -1 /dev/tty.*
/dev/tty.KeySerial1
/dev/tty.USA192433P1.1

Once you identify the USB-to-Serial adapter, in this case, USA192433P1.1, you can connect using tip(1)/cu(1) or screen(1). I used tip on my iBook, but don’t have it installed on my iMac.

% screen /dev/tty.USA.192433P1.1

Check the screen manpage for details about setting baud rate and other options.