Important!
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This readme file applies only to MAC OS X version starting with 10.7 (incl.) and beyond. 
Composite CDC + (any other interface) USB devices (such as the MCP2200 & MCP2221, which 
are composite CDC+HID devices) will only work on Mac OS X 10.7 (or later). 
Mac OS X 10.7 is the first OS X version that supports USB Interface Association
Descriptors (IADs), which are needed when implementing composite USB devices with multiple 
interfaces, with at least one CDC-ACM function. Prior versions of Mac OS X did not support 
IADs, and therefore can only support non-composite, single function CDC-ACM devices.

Upon plugging in a USB CDC ACM virtual COM port device into a Mac OS X based machine, 
the OS should automatically enumerate the USB device successfully, and a new object 
should show up as:
/dev/tty.usbmodemXXXX
(where XXXX is some value, such as “fd1321”)
To test the CDC functionality a procedure like follows can be used:

Open TERMINAL. This can be done by clicking SPOTLIGHT and searching for TERMINAL. 
Spotlight is the little magnifying glass in the upper right of the screen.
In Terminal, with the USB CDC ACM device NOT plugged in (yet), type:
ls /dev/tty.*

This will show all serial devices currently connected to the Mac. In the author’s case, 
the following list appears:
/dev/tty.Bluetooth-Modem
/dev/tty.Bluetooth-Incoming-Port
/dev/tty.BluePortXP-115D-SPP

Now, plug the MCP2200 or MCP2221 device into a USB port of the Mac. Hit the UP cursor, 
which will bring the search command back ( ls/dev/tty.* ) and hit return. 
You should get the exact same list as before, but this time, with a new serial device. 
In the author’s case, it was:
/dev/tty.usbmodemfd1321

Once the complete name is know, the received serial port data can be displayed by typing:
screen /dev/tty.usbmodemfd1321
(replace “fd1321” in the above line with the value for your machine). 

The baud rate can be set by using syntax like follows:
screen -U /dev/tty.usbmodemfd1321 115200
Where “usbmodemfd1321” should be replaced with the actual value of the device, and “115200” 
should be replaced with actual desired baud rate (ex: 9600, 19200, 38400, 57600, 115200, etc.). 
More details and usage information for screen can be found in the man page of the "screen" utility.

A number of serial port utilities can be found on the App Store. "Serial Tools" is a good example 
of a free serial terminal application.