If server receives the request and detect an error on the communication channel (e.g parity, LRC, CRC), server will not response anything to the client. Client will then have the timeout request error.
* If server receives the request and is unable to execute it (e.g client requests to read a non-existent register), server will return an exception response to client to indicate the nature of the error.Exception response message includes two other fields when compared to a normal response message:

* Function Code: Function code's