That's alright but there is a simulator package that providing you have a real plc(processor), the software is called PICS, this package is excellent in most cases it is best to copy the real Inputs to internal memory bits in a block, disable this block for simulation (no need to have real I/O) unfortunately this software is quite expensive & will require an I/O driver or opc server to communicate with the plc.
I have used pics on many large applications you can simulate very complex situations in full, speed up or slow down real time & it will give you reasonable graphics although not as good as a full blown scada package.
You use the standard functions supplied or create your own, the logic to control the functions is in ladder so easy to use but also very powerfull.
However due to the high cost mainly systems houses use it as every plc will need a licenced driver or opc server.
plc sim is a bit basic but ok for small simulations I'm sure there are other packages out there as well, in the old S5 days an ex siemens employee created a system call prosis, this was software on a pc with interface cards that plugged into the S5 rack, the function control was written in pascal, but this was dedicated to siemens.