DDR2 RAMs have these control signals
RAS, CAS - address strobes
UDQ, LDQ - byte strobes
WE - write enable
UDM, LDM - write mask
Why do we need UDM and LDM? Can't you write a byte by asserting WE and only one DQ?
Here's a link to a typical data sheet. It tells me what the write mask does, but not why I need it. https://www.alliancememory.com/wp-content/uploads/pdf/ddr2/AS4C32M16D2A-25BAN_rev1.5.pdf