64Mb: x32 SDRAM
Bank/Row Activation
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.
After a row is opened with the ACTIVE command, a READ or WRITE command can 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 15 (page 43), 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 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 mini-
mum time interval between successive ACTIVE commands to different banks is defined
by
t
RRD.
Figure 15: Example: Meeting
t
RCD (MIN) When 2 <
t
RCD (MIN)/
t
CK < 3
T0
T1
T2
T3
CLK
tCK
tCK
NOP
tRCD(MIN)
NOP
tCK
READ or
WRITE
Command
ACTIVE
Don’t Care
PDF: 09005aef811ce1fe
64mb_x32_sdram.pdf - Rev. T 04/13 EN
43
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1999 Micron Technology, Inc. All rights reserved.
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