about 'DQM',‘CKE’，’WE‘ of emif in rm48L950's schematic design

please give help,my question is:

1:why use SN74CBTLV3245ARGY,and pull up 'DQM', when connect DOM of sdram chip to rm48L950?

2:why use SN74CBTLV3245ARGY,and pull down 'CKE', when connect DOM of sdram chip to rm48L950?

3:why not use SN74CBTLV3245ARGY,and pull down or pull up WE, just like 'DQM' or 'CKE',when connect 'DOM' of sdram chip to rm48L950?