Dear all, I have a working program which has been running for about a year. This project uses the AT89C51ED2 from Atmel. Seeing as I was using uV Version 7.02 which didn't support this chip I decided to upgrade and am now running V7.50a (I believe the latest). I did some alterations on the above mentioned project like changing timers and including the origional keil header file instead of the one I altered myself, and then recompiled. Tested the project in the simulator, everything seems ok. Then I flashed a chip and.... nothing.... Even the Outputs didn't get set to "0". After examining the header files I came accross the following differences. Old altered file: sbit P1_7 = P1^7; sbit P1_6 = P1^6; sbit P1_5 = P1^5; New AT89C51XD2.h file Sbit (P1_7 , 0x90, 7); Sbit (P1_6 , 0x90, 6); Sbit (P1_5 , 0x90, 5); etc...etc...etc... In my progarm I have the following: sbit relais = P1^1; sbit active = P1^0; etc...etc... The question: Could this be the cause of the problem? If so, why don't I get compiler errors? Thanks in advance for any responses. Regards John Garrelts