512Mb: 32 Meg x 16, 16 Meg x 32 Mobile SDRAM
Operations
Upon exiting the self refresh mode, AUTO REFRESH commands must be issued every
7.8125µs or less as both SELF REFRESH and AUTO REFRESH utilize the row refresh
counter.
Deep Power-Down
Deep power-down is an operating mode used to achieve maximum power reduction by
eliminating the power of the whole memory array of the devices. Array data will not be
retained once the device enters deep power-down mode.
This mode is entered by having all banks idle then CS# and WE# held LOW with RAS#
and CAS# held HIGH at the rising edge of the clock, while CKE is LOW. This mode is
exited by asserting CKE HIGH.
Operations
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 9 on page 23).
After opening a row (issuing an ACTIVE command), a READ or WRITE command may be
issued to that row, subject to the
t
RCD specification.
t
RCD (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
t
RCD specification of 20ns with a 125 MHz clock (8ns period)
results in 2.5 clocks, rounded to 3. This is reflected in Figure 10 on page 23, which covers
any case where 2 <
t
RCD (MIN)/
t
CK
≤
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
t
RC.
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
t
RRD.
PDF: 09005aef81ca5de4/Source: 09005aef81ca5e03
MT48H32M16LF_1.fm - Rev. H 6/07 EN
22
Micron Technology, Inc., reserves the right to change products or specifications without notice.
©2005 Micron Technology, Inc. All rights reserved.
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