ReadSerialPortx Questions

[Nathan]

When the function ReadSerialPortx is called does it actually read from the serial port, or does it read a byte from the input circular buffer?

If the ReadSerialPortx function does read from the buffer, I'm assuming the data from the serial ports is automatically stuffed into these buffers? As in, I don't need to write a routine to fill the buffers with data?

And finally, how large are the input and output ring buffers? I need to know how fast I need to retrieve data from them so overwrites don't occur.

TIA,
Nathan