can u see any problem in the looping
I do not know if micro can see any problem, but you need go to links <-- and find best serial appnotes and read "ten ways to bulletproof RS-485 circuits. If all ten ways are followed, and it still does not work, you can be sure you have a software problem.

One common problem is switching direction immediately in the ISR for the last RI/TI interrupt, that is a mistake. The interrupt does NOT happen at the end of the stop bit. For exact timings, have a loook in "the bible" chapter 3.

Erik