Hi, I was using 89C52 for my project. It worked fine but due to larger code size. I have to shift to 89C55WD. But the problem is that when i first burnt the code in the microcontroller, every thing was fine. But after serial reception it came to hanging state. And then it is not responding after that. It has happened to me twice. There is no pb in circuit, i have already checked. If anyone has solution please help me. Thanks Afshan