In reply to szy0014:
Your for loop does not make any sense because each iteration overwrites the previous value of hold_data. Also what is the relationship between data and wr_data. Where is the declaration of wr_data.
The range you are trying to describe [(iWORD_SIZE) : (iWORD_SIZE + (WORD_SIZE-1))] should be written as [(i*WORD_SIZE) +: WORD_SIZE].
You may want to take a look at the streaming pack/unpack operator in the LRM