how can we transfer variable from S7 to WINCC

dear experts:
normally if there is a PCS7 multiproject,when we compile the intergrated OS,all variables got the property of "S7_m_c"will be transferred to wincc automatically. now there is a S7 project communicating with WINCC,and all the variables in the sub-folder of TCP/IP are DB(show in the document "variable of WINCC"),but when i check the same DB in the S7 project,we can not find "s7_m_c" in it's property,so how can we transfer the variable from S7 to WINCC?