64Mb: x32
SDRAM
Operation
BANK/ROW ACTIVATION
Before any READ or WRITE commands can be is-
sued to a bank within the SDRAM, a row in that bank
must be “opened.” This is accomplished via the AC-
TIVE command, which selects both the bank and the
row to be activated. See Figure 3.
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 issued. For example, a
t
RCD specifi-
cation of 20ns with a 125 MHz clock (8ns period) results
in 2.5 clocks, rounded to 3. This is reflected in Figure 4,
which covers any case where 2 <
t
RCD (MIN)/
t
CK - 3.
(The same procedure is used to convert other specifi-
cation 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 mini-
mum time interval between successive ACTIVE com-
mands 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 over-
head. The minimum time interval between successive
ACTIVE commands to different banks is defined by
t
RRD.
Figure 3
Activating a Specific Row in a
Specific Bank
CLK
CKE
CS#
HIGH
RAS#
CAS#
WE#
A0–A10
ROW
ADDRESS
BA0, BA1
BANK
ADDRESS
Figure 4
Example: Meeting
t
RCD (MIN) When 2 <
t
RCD (MIN)/
t
CK - 3
T0
CLK
tCK
COMMAND
ACTIVE
NOP
tRCD (MIN)
tRCD (MIN) +0.5 tCK
tRCD (MIN) = 20ns, tCK = 8ns
tRCD (MIN) x tCK
where x = number of clocks for equation to be true.
tCK
NOP
tCK
READ or
WRITE
T1
T2
T3
DON’T CARE
64Mb: x32 SDRAM
64MSDRAMx32_5.p65 – Rev. B; Pub. 6/02
12
Micron Technology, Inc., reserves the right to change products or specifications without notice.
©2002, Micron Technology, Inc.
MICRON [ MICRON TECHNOLOGY ]
