Acess data wordwise from Nios II

If anybody has the same question here is the response I got from the Altera support:

For masters, the address signal represents a byte address. The value of the address must be aligned to the data width. To write to specific bytes within a data word, the master must use the byteenable signal. For slaves, the inter-connect translates the byte address into a word address in the slave’s address space so that each slave access is for a word of data from the perspective of the slave. For example, address= 0 selects the first word of the slave and address 1 selects the second word of the slave.

Please refer to the following user guide page 30 "Avalon MM salve addressing".

http://www.altera.com/literature/manual/mnl_avalon_spec.pdf