How to receive stream of bytes using PIC USART

[unifoxz]

I am sorry for the confusion. Actually, the following code is to wait for the PC to send the request before PIC read in the data from the SpO2 module.

'request from PC, 9600 baud rate
standby:
SerIn PORTC.7,6,["P",ID_2, ID_1, ID_0]

Once PIC get the matching ID from PC, the PIC will read the data from SpO2 module to extract the SpO2 byte and pulse rate byte from the SpO2 module. Since PC and SpO2 module are using different baud rate (which PC is 9600 baud rate and SpO2 module is 4800 baud rate), I can't put them in the suggested code line.

The PIC need to capture 2 bytes from a stream of bytes sent by the SpO2 module. The SpO2 module sends the bytes in sequence and continuously. I get the wrong data but I think there is nothing wrong with my algorithm to capture the intended data, by referring to the manual of the SpO2 module.

My guess is that the PIC's receiver buffer has overflowed and causing the data clash. How should I avoid the buffer overflow so that I could retrieve the correct data byte from the byte stream of the SpO2 module?