Attached as a ZIP file to this page is a simple CDC (Communications Device Class) implementation for the PIC18F2455, using SourceBoost C. I did not write this from scratch, but borrowed on USB HID sample code by Robert Lang, who in turn credited Reston Condit, Dan Butler and Andrew Smallridge. I wanted an easy to use/easy to follow "one file" implementation of a USB CDC device, an could not find anything that was quite what I wanted.

 

To use this code you'll need a working PIC18F2455 USB circuit with 20MHz crystal. And of course you'll need SourceBoost C and a PIC programmer..