Hi Zen,

Profibus is not as easy as e.g. Modbus.
Your Master first reads the GSD file (kind of electronic data sheet) and 
with the information contained there and additional parameters you may 
enter ,then sends configuration data to your slave.
After that the master polls all connected devices (only one in your 
case).
With different services the master now can read/write information 
from/to the slave device.

You have to know the structure of the data within your Profibus slave 
and the service to access them.

Without much deeper knowlege of Profibus, I don't think you will be able 
to write your own communication interface.
I have attached screen shots from an old Profibus specification (it is 
protected) which shall only indicate the complexity. The Profibus spec 
is part of an international standard and thus no longer available for 
free.

You should look at technology companies which offer solutions in 
industrial communication (e.g. Hilscher, HMS, Molex). They have scalable 
solutions from  code to chip to modules.

I have done internal Profibus certification for a couple of years but 
all devices I have seen made use of a standard front-end from one of the 
above mentioned companies.

wish you best luck with your Profibus
Ulrich