Just bumping this old thread as i want to revisit the idea.

I don't have access to the transmitting device so can't add bits or change format etc.
I can't use handshaking etc.
My PIC18F2680 Hardware Usarts/hserin etc are already committed.

I want to trigger an interrupt when a pin goes low (it idles high) then receive that incoming serial data with Serin2
If it jumps to the Serin2 quickly enough will it work? Or will I lose that first bit.

The actual first byte of incoming data isn't critical (it's a header) but the next 4-5 bytes are.