256Mb: x4, x8, x16 SDRAM
AUTO REFRESH Operation
AUTO REFRESH Operation
The AUTO REFRESH command is used during normal operation of the device to refresh
the contents of the array. This command is nonpersistent, so it must be issued each
time a refresh is required. All active banks must be precharged prior to issuing an AUTO
REFRESH command. The AUTO REFRESH command should not be issued until the
minimum tRP is met following the PRECHARGE command. Addressing is generated by
the internal refresh controller. This makes the address bits “Don’t Care” during an AU-
TO REFRESH command.
After the AUTO REFRESH command is initiated, it must not be interrupted by any exe-
cutable command until tRFC has been met. During tRFC time, COMMAND INHIBIT or
NOP commands must be issued on each positive edge of the clock. The SDRAM re-
quires that every row be refreshed each tREF period. Providing a distributed AUTO RE-
FRESH command—calculated by dividing the refresh period (tREF) by the number of
rows to be refreshed—meets the timing requirement and ensures that each row is re-
freshed. Alternatively, to satisfy the refresh requirement a burst refresh can be employed
after every tREF period by issuing consecutive AUTO REFRESH commands for the num-
ber of rows to be refreshed at the minimum cycle rate (tRFC).
PDF: 09005aef8091e6d1
256Mb_sdr.pdf - Rev. R 10/12 EN
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