The blue mini-USB console cable that is included with the IR829 (and other 800 series devices) connects the mini-USB console port, under the screwed down plate, to a USB port on your Mac.
To use the "screen" command on OSX El Capitan 10.11 to connect to the console on the IR829, you need install a new set of CP210x USB to UART Bridge VCP Drivers. Then you can:
screen /dev/cu.SLAB_USBtoUART4 9600
I will say that the Serial application is very good, and it was the Serial support team who helped me figure this out. Yes, it does cost $30, but it just works (TM). Also see The specified message was not found..
When using Serial you will need to open (Command-o) a terminal window, whereupon you will be presented with an "Open Port" window, which will allow you to select one of, in my case, two USB to UART bridges. In my case, it was #2 that worked. When then terminal window opens, you will need to open the settings (Command-;) and set the "Terminal Settings->Configuration" option to be "Cisco".
Also see How to use a Serial-USB Console Cable with the IR829 and OSX El Capitan 10.11,How to use the IR829 Mini-USB Console Cable with Windows 10 and How to use the IR829 Mini-USB Console Cable with Linux.
