what is the reason for data mask pin in DDR3

[FixitFast]

Hi all


what is the reason of data mask pin in DDR3. What if I make it disable?


please reply

 

[kripacharya]

possibly RTFM might lead you to your answer.
Most likely if you disable DM, then the data will not get masked. Yes ?

cheers!

 

[permute]

It allows writes at 1B granularity. For example, if you need to write exactly 1B to RAM and you have a 64b bus (8B wide) and burst length is set to 8, then the smallest size of data you can write would be 8*8=64B (or 512b). With the data mask, you can mask off 7B of one access, and then mask off all 8B of the remaining 7 accesses in the fixed-length burst.

For similar reasons, it allows you to write 2B or 4B at a time as well.

Otherwise you would need to do a read-modify-write any time you wanted to write less than 64B to RAM!