Hi,

If you do not elaborate your question it is very difficult to answer. The Serin command is a software driver serial TX/RX routine. So until and unless you are doing it often you may miss some data. A faster approach is to use to CTS, RTS lines on your ports by which you can control the handshaking by the PIC itself. Some PICs feature a hardware UART, which makes your life a little easier. So we need the PIC you are using and the intention of your program.

Regards

Sougata