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128Mbx16x32Mobile_2.fm - Rev. M 1/09 EN
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2001 Micron Technology, Inc. All rights reserved.
128Mb: x16, x32 Mobile SDRAM
Register Definition
Upon exiting the self refresh mode, AUTO REFRESH commands must be issued every
15.625s or less because both SELF REFRESH and AUTO REFRESH utilize the row
refresh counter.
Self refresh is not supported on automotive temperature (AT) devices.
Operation
BANK/ROW ACTIVATION
Before any READ or WRITE commands can be issued to a bank within the SDRAM, a row
in that bank must be “opened.” This is accomplished via the ACTIVE command, which
selects both the bank and the row to be activated (see
Figure 10).After opening a row (issuing an ACTIVE command), a READ or WRITE command may be
issued to that row, subject to the tRCD specification. tRCD (MIN) should be divided by
the clock period and rounded up to the next whole number to determine the earliest
clock edge after the ACTIVE command on which a READ or WRITE command can be
entered. For example, a tRCD specification of 20ns with a 125 MHz clock (8ns period)
any case where 2 < tRCD (MIN)/tCK ≤ 3. (The same procedure is used to convert other
specification limits from time units to clock cycles.)
A subsequent ACTIVE command to a different row in the same bank can only be issued
after the previous active row has been “closed” (precharged). The minimum time
interval between successive ACTIVE commands to the same bank is defined by tRC.
A subsequent ACTIVE command to another bank can be issued while the first bank is
being accessed, which results in a reduction of total row-access overhead. The minimum
time interval between successive ACTIVE commands to different banks is defined by
tRRD.
Figure 10:
Activating a Specific Row in a Specific Bank
CS#
WE#
CAS#
RAS#
CKE
CLK
A0–A10, A11
ROW
ADDRESS
DON’T CARE
HIGH
BA0, BA1
BANK
ADDRESS