According to the list at http://www.keil.com/update/versions.asp the current version of C51 is V6.11. The compiler we're using is V6.10 (reported by uVision and also by c51 from command line), after downloading and installing V6.10a from the web. What's the difference between V6.10 and V6.11? Is it wise to upgrade? Where to get V6.11? Loet Heinemans