Hello everyone,
Why some C files are in red (indicates that an error has been occure)?
http://www.keil.com/support/man/docs/uv4/uv4_ca_filegrp_att.htm
You're using unlicensed features. Presumably an Eval or Lite version of Keil.
how to install a licensed version?
When you buy the licence, you will get instructions with it!
http://www.keil.com/support/man/docs/uv4/uv4_dg_lic_mgmt.htm
To buy a license, get in touch with your local distributor:http://www.keil.com/distis/You can also request a free of charge 30 days time limited MDK Pro license for the purpose of evaluation.