Hi Sreerama,
Which K20 MCU are you using? Maybe the following post created by our colleague Erich Styger is helpful for you, it explains the usage of the FRDM-K20D50M as USB CDC with Processor Expert:
https://mcuoneclipse.com/2013/04/27/usb-cdc-with-the-frdm-k20d50m/
Hope it helps!
Best Regards,
Carlos Mendoza
Technical Support Engineer
-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------