Try the same test without 485. I.e. connect the 8052 to the PC without going through 485. I used to do development that required going through a 485 network and when the 485 convertor went bad you get all kinds of wonderful and confusing results. Whenever I had a communication problem with code that I knew worked the first thing I would do is try taking the 485 out of the equation.

If the problem persists after dropping back to RS232 then it requires further investigation. If it works with pure RS232 then you know you have a 485 problem.

Regards,
Craig Steiner