64Mb: x32
SDRAM
BURST TERMINATE
SELF REFRESH
The BURST TERMINATE command is used to trun-
cate either fixed-length or full-page bursts. The most
recently registered READ or WRITE command prior to
the BURST TERMINATE command will be truncated,
as shown in the Operation section of this data sheet.
The SELF REFRESH command can be used to retain
data in the SDRAM, even if the rest of the system is
powered down. When in the self refresh mode, the
SDRAM retains data without external clocking. The SELF
REFRESH command is initiated like an AUTO REFRESH
command except CKE is disabled (LOW). Once the SELF
REFRESH command is registered, all the inputs to the
SDRAM become “Don’t Care” with the exception of
CKE, which must remain LOW.
Once self refresh mode is engaged, the SDRAM pro-
vides its own internal clocking, causing it to perform its
own AUTO REFRESH cycles. The SDRAM must remain
in self refresh mode for a minimum period equal to
tRAS and may remain in self refresh mode for an indefi-
nite period beyond that.
The procedure for exiting self refresh requires a se-
quence of commands. First, CLK must be stable (stable
clock is defined as a signal cycling within timing con-
straints specified for the clock pin) prior to CKE going
back HIGH. Once CKE is HIGH, the SDRAM must have
NOP commands issued (a minimum of two clocks) for
tXSR because time is required for the completion of any
internal refresh in progress.
AUTO REFRESH
AUTO REFRESH is used during normal operation of
the SDRAM and is analagous to CAS#-BEFORE-RAS#
(CBR) REFRESH in conventional DRAMs. This com-
mand is nonpersistent, so it must be issued each time
a refresh is required.
The addressing is generated by the internal refresh
controller. This makes the address bits “Don’t Care”
during an AUTO REFRESH command. The 64Mb
SDRAM requires 4,096 AUTO REFRESH cycles every
64ms (tREF), regardless of width option. Providing a
distributed AUTO REFRESH command every 15.625µs
will meet the refresh requirement and ensure that each
row is refreshed. Alternatively, 4,096 AUTO REFRESH
commands can be issued in a burst at the minimum
cycle rate (tRC), once every 64ms.
Upon exiting SELF REFRESH mode, AUTO REFRESH
commands must be issued every 15.625ms or less as
both SELF REFRESH and AUTO REFRESH utililze the
row refresh counter.
64Mb: x32 SDRAM
64MSDRAMx32_5.p65 – Rev. B; Pub. 6/02
MicronTechnology,Inc.,reservestherighttochangeproductsorspecificationswithoutnotice.
©2002,MicronTechnology,Inc.
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