Do you have some reason to believe all data wasn't sent? How much data are you sending? I've usually seen RS485 used for rather simple protocols that send packets of relatively small amounts of data (less than 256 bytes) and then wait for some kind of ACK and perhaps send more data.

The protocol you implement will, by itself, assure that all data was sent. If all data wasn't sent you presumably won't get an ACK and will try again. Since the packet size is small you don't lose much by repeating packets--unless there's a significant amount of noise that constantly corrupts the communication.

Craig Steiner