reading without losing data

This post is concerned with reading data ,without losing data, from serial port(rs232).
Please tell the asembler code for achiving this.

I comunicate with asynchronous device
(fiscal device for collecting data for sales in shops and calculate the tax) .
Cominication is with 8 bits,none parity and 1 stop bit and 9600 b/s.
Also this charactersiatics are in device menager for comport 1
(Also i think that is not necessary to care for them in the code).
I/O adress for comport1 are 3F8-3FF and IRQ4.

Also please tell me the adress for command and status register
for appropriate component
which take care foe this type of comunication.

Thanks advance