...REFRESH REQUIREMENTS
DDR SDRAMs require a refresh of all rows in any rolling 64 ms interval. Each refresh is generated in one of two ways: by an explicit AUTO REFRESH command, or by an internally timed event in SELF REFRESH mode...
...AUTO REFRESH
AUTOREFRESH is used during normal operation of the DDR SDRAM and is analogous to CAS–BEFORE–RAS (CBR) refresh in previous DRAM types. This command is nonpersistent, so it must be issued each time a refresh is required.
The refresh addressing is generated by the internal refresh controller. This makes the address bits ”Don’t Care” during an AUTO REFRESH command. The DDR SDRAM requires AUTO REFRESH cycles at an average periodic interval of tREFI (maximum)...