ByteIO component instead of BitsIO component should be used when whole port is accessed. The BitsIO component is intended for accessing only part of the port (e.g. 4 bits of 8- bit port)
Using the BitsIO component results more complex code because this component provides more general code for the methods, which allows access to only some of the bits of the port. On the other side, the ByteIO component provides access only to the whole port and thus the resulted code is optimized for such type of access.