Hi, I am currently trying to get my code support two different type of LCD display, the only difference is the hardware level driver, so condional compilation directive has to be introduced. #ifdef DISPLAY_1 void display_driver() { // do one thing } #else void display_driver() { // do another thing } #endif However I don't want change the directive in the code, I would like to do it in the IDE, I guess it should be under project\option\C51, any one know how to do it ? Thanks in advance. Daniel