Memory-mapped ports often have different properties than normal RAM:
* A read-only The contents of a port is what it sounds likecan be updated by the hardware. Attempting to write to this address Reading a port will not affect always return the contentssame value each time it is read. * It is also possible that reading a port will alter its contents, or alter the contents of other related ports. * A read-only port is what it sounds like. Attempting to write to this address will not affect the contents.
* A write-only port can be written to, but reading it will result in undefined behavior. The value read from the address is not necessarily what was last stored in it.