Hi, i figure out the problem, but not the cause.
Seems like when i working with the 328p, when i send some data via 485, "somehow" he receives also the same thing, what is impossible because with the 485 i receive or send, never at the same time.
With 2560 this problem never occurs, and it have the same code.
It is not a problem with memory i can ensure you.
The solution: After send some data i read all the RX buffer to clean it.