I'll assume you are using an imbedded system or something to that effect here since as Salem said normally you can't just grab an address like that.
You should be fine doing this:
Also, assuming you do have access to this memory address I'd advise that you be careful. Usually a person asking this question is one who really shouldn't be trying to do this (you would already know what to do). It is possible that this an address contains information that is crucial to your OS. Furthermore, you can really screw up things if by tinkering with system information. It usually would require a reboot, but I've heard of cases where the OS has been corrupted.
unsigned int *pAddr = (unsigned int *)0x80000000 ;