How to use the exceptions in a RFC ?

I can use XI (through BPM) to call a RFC and get response from the "Export" of a RFC. But could I get the exception from the "exception" of a RFC ?

I tried to write a RFC which will generate a exception and I found it in the XI monitor, but how to use it ? i.e. sometimes I need to get the "export", but sometimes I need to get "exception". Is there any documents or examples for it ? thanks.