Uh, perhaps the OP means a S7-200 plc ? 'Cause a Siemens S700 is a phone.
In cay case, please post to whole part number xxxx-xxxx-xxxx-xxx like, as you may have a plc that does not accept 24vdc on inputs.
If you do, then connect the one of the wires of the prx switch to the input terminal. The other wire(s) connection depend on the switch type.