The busy flag can only polled outside the interrupt function in the application.
1.) before you send any data from the uart you have
to switch on the tx enable line of the RS485 transceiver
3.) switch off the tx enable line of the RS485 transceiver
immediately after the last stop bit from the last byte
of the transmitting frame ist sendet out from the uart
this all should be done in the uart ty interrupt handler,
the application only fills the software fifo and starts the
Retrieving data ...