I just took a look at the manual and you are right, it's not clear enough.
SRAMs in DLS are word-addressable memories. If your word size is larger than 8 bits (Din width greater than 8) you have more than 1 byte per word. \bwe is an active low signal controlling which bytes of the addressed word will be written (bwe = byte write enable).
E.g. if your word size is 16 bits and you address size is 8 bits, it means that you have 256 words or 512 bytes. But since you can only access individual words (i.e. byte pairs) you can only read or write bytes starting at even addresses. What would you do if you wanted to write only byte #5 which is the 2nd byte of the 3rd word? You should set the inputs to the following values:
- addr = 02h
- Din = XX12h, where XXh can be any value (SRAM should not care)
- \bwe = 10b
This way, on the next rising edge of clk, only the 2nd byte of the 3rd word will be overwritten, leaving the 1st byte intact.
Hope it clears things up a bit. If not, I'll try a more concrete example.