Elevator with S7 300???

Greetings,

I'm student and I would like to program PLC for 4 floor elevator in FBD, it will be just simulation, but maybe we'll realize it in college. So all inputs and outputs are on simulator. It'll have this:
- Switches in & out elevator
- Switch on every floor to figure on which floor is elevator
- Door close switch
- Emergency stop switch at top and bottom of elevator shaft
- Output are two digital outputs (elevator up, elevator down)
First problem for me is logic of elevator, how can I make elevator to go where I want. I found this picture http://img83.imageshack.us/img83/976/elevatorw.jpg but I don't know how this mul works? Can you please tell me how can I on easiest way program this movement?

Thank you on any help!

There is a load on here about lifts.... try search facility

Ideas for you

Use integers for your floor numbers (0 = ground, 1 = 1 etc)

Use a integer for current position, use integer for required position.

Then, if required > actual go up, if required < go down

When lift hits floor position switch, move the floor number into the actual position register.

If actual= required, you have reached your required floor.

Maybe have a DB to contain requested floors so you stop if floor is in DB

Dont want to do the poject for you

Cheers