I am trying to read data back data on my USART0 RX pin on my ATmega324P. The data being return from the modem is +CMTI: "SM",1. When this data is received I am trying to fire the RX interrupt but it will not fire. So my question is, will the interrupt only fire with 8 bits, and anything larger it does not fire? I have tried the overflow interrupt but that does not work either.