communication with S7 300

Hey guys, i have a PPI/485-USB cable which is made by seimens co. and i want to use it to communicate with a S7 300 and i set the PG/PC interface to PPI/Pc cable with a USB as a local connection but when i try to upload the station program to my pc this message appears
"With the set interface configuration, communication in STEP7 is not possible"

Please help me out what i did wrong and how i can communicate with the PLC S7 300 to upload and download stuff?!!

When you see ur SET PG-PC interfac do u get the name of the software what u have installed like when we install CP5512 card we will get the opetion CP5512 AUTO ,CP5512 MPI ,CP5512 PROFIBUS if yes you get the similar options like PPI/PC AUTO,MPI,PROFIBUS then u can select the option PPI/PC auto and then check the BAUDE RATE to which your RS 422 port i.e MPI/DP is set to then try to down load .... it may work all the best

PPI is the protocol of S7-200 series.

S7-300s uses MPI,Profibus DP(Optional), Profinet (Optional)

To be able to communicate with S7-300 CPUs you need MPI/Profibus DP Adapter or CP 5511,CP5512 PCIMCIA cards.

Have a good day.