First configure the touch screen controller ADS7843 according to your uart settings. This can be done by sending the control bits to the ADS7843 through TX pin of MCU. Then wait till a data frame arrives through the RX pin of MCU and read it.
You might have done coding for uart module. If it is so then all you have to do is to send the controll commands according to the datasheet and receive the data from the ADS7843, decode it according to the information given in the datasheet.
If you haven’t done any coding for uart yet, suggest you to try basic uart interfacing codes.
Go through the datasheet of ADS7843 in detail and learn more.