"Don't ask me how it works though, i just copied it"

That can be very dangerous approach - especially where pointers are concerned! :-0

But you are correct: it is casting the value 0x00 to a function pointer.

So the question now is, does Siti just want to know how to do a software reset, or is this really a question about How to add assembly to Keil C51 - as the subject line says?