You can connect via the command line
Use the built in Unix program called: screen
Open Utilities folder, open Terminal.
You'll see a black terminal window.
You can see some of the screen commands by typing: man screen
That will pull up the sceen manual pages.
I connect to my USB serial device with the command:
screen /dev/tty.usbserial 9600
This also works:
screen /dev/tty.PL2303-0000201A
The actual tty name may change depending on what kind of USB Serial Adapter you are using.