S7-300 and libnodave

I need your help. I want to use libnodave to communicate with S7-300. I created a Win32 console project first, added testMPI.c and other related files.

I compiled the project successfully, but it can not read bytes from PLC. I stepped in the program, the return of function davaInitAdapter() is always not 0.

I used PC adapter USB. But, in testMPI.c, the function setport() is for serial port in my opinion, I guess it is the problem.

Please give me your suggestion. Thank you very much!