http://support.automation.siemens.com/CN/view/en/36068796

Service Pack 3 (SP3) for S7-PLCSIM V5.4 provides the following new functions:

Multiple startability (multi-instance capability) and communication support between the simulated CPUs (simulation instance)
Optimized download by omitting the Node Browser
Support of an additional PG/PC interface: PCinternal (local)
Optimization of the communication between S7-PLCSIM and WinCC / WinCC flexible
Indication of all CPU access addresses in the status line