Hi Mike,

Welcome to 8052.com. This is only a guess, and I am assuming that you've built your own circuit because you described individual components. If you simulate your program and it works, and assuming you have all of the pins configured properly (like EA as Mehdi pointed out), then my guess would be that you're not getting a clean boot up. If you use the simple RC circuit that the data sheet calls for to provide power up reset, then it's a good bet that you aren't booting up properly. This is even more likely if you've put your circuit together with friction connections.

I know, I know. The manufacturer's data sheet says all you need is the one capacitor. In short, they lied. Do a search of the forum for "reset" and you can read far more than I'm willing to type on the subject. I will, however, make the point by pointing out that you will never find one of the manufacturer's demo-boards that uses the RC reset circuit. Why do you suppose that is? In the meantime do yourself a favor and get a reset supervisor.

Good luck,

Joe