Re:Can any PIC wake up from UART interruption?
I think some PICs have an option to wake from UART, but they will not normally capture the first byte during wake-up.
I have previously implemented your idea of using external interrupt connected to RX line to wake up the PIC. Despite what you may have read, I was able to successfully capture even the first byte! The trick is, you must wake up into a clock source that has very fast start up time. In other words, no crystals and no PLLs. EC is the fastest, but generally not very useful because leaving an EC running during sleep kind of defeats the purpose (the EC will draw too much current).
For me, I had the PIC wake up on INT0 falling edge (start bit) and used 8MHz INTOSC. The INTOSC started up fast enough that the PIC was up and running with the RX line still in the Start Bit state. That allowed me to capture the very first byte of data on the UART, no problem.