Arduino module modbus

[maxtisc]

hello team
in a project I receive the impulses from an external module and recalculate them in speed, I am proceeding step by step and everything worked well, now implementing the rs485 modbus module, but at the end of the compilation it gives me a series of errors

C:\Users\Max\Dropbox\radar\radar_AN_arduino_modbus.c: At top level:
C:\Users\Max\Dropbox\radar\radar_AN_arduino_modbus.c:5690: error: redefinition of '__vector_51'
C:\Users\Max\Dropbox\radar\radar_AN_arduino_modbus.c:5656: error: previous definition of '__vector_51' was here

also in the icon list they appear other errors that were not there before
I hope you can help me
thanks

[maxtisc]

hello team
I'm very happy because I managed to make modbus work, the problems were multiple from the wiring and the software, but now everything is ok, I only have 2 questions:
1) does it make sense to use an interrupt on the rx pin of the 485?
2) the last bytes of the transmission from what I understand are the CRC, how are they generated?

thanks