data format of RS232 com. protocol

Hi
I have interface a cash Register with a computer, now through RS232 communication i want to communicate with the cash register, what ever transcations which are occuring there in cash registers should be stored in my computer, so i want to capture the data from the cash register, Can any body tell me the data coming from cash register is in which format, and how to insert it into a text file.
pls guide

rgds
Anupam Srivastava