Hi, using C inside the Keil 7.0 Tools i have a strange behaviour. some defines / includes ... #include "mycpu.h" .. #define LCD_Port P2 #define RS P2_1 #define LOW = 0; ... void function1(unsigned char temp) { ... LCD_Port = temp; RS = LOW; // this two lines are not executed, using the debugger, the debugger jumps over these lines ... } void function2(unsigned char temp) { ... LCD_Port = temp; // this line is executed ... } Why? Thank you in advance Axel