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20
64Mb: x32, 3.3V SDRAM
BatRam_3V.p65 – Rev. 0.7, Pub. 2/01
Micron Technology, Inc., reserves the right to change products or specifications without notice.
2001, Micron Technology, Inc.
64Mb: x32, 3.3V
SDRAM
PRELIMINARY
Figure 18
WRITE To PRECHARGE
Figure 17
WRITE To READ
Figure 16
Random WRITE Cycles
CLK
DQ
D
IN
n
T2
T1
T3
T0
COMMAND
ADDRESS
WRITE
BANK,
COL
n
D
IN
a
D
IN
x
D
IN
m
WRITE
WRITE
WRITE
BANK,
COL
a
BANK,
COL
x
BANK,
COL
m
NOTE:
Each WRITE command may be to any bank.
DQM is LOW.
CLK
DQ
T2
T1
T3
T0
COMMAND
ADDRESS
NOP
WRITE
BANK,
COL
n
D
IN
n
D
IN
n
+ 1
D
OUT
b
READ
NOP
NOP
BANK,
COL
b
NOP
D
OUT
b
+ 1
T4
T5
NOTE:
The WRITE command may be to any bank, and the READ command
may be to any bank. DQM is LOW. CAS latency = 2 for illustration.
DON’T CARE
DQM
CLK
DQ
T2
T1
T4
T3
T0
COMMAND
ADDRESS
BANK
a
,
COL
n
T5
NOP
WRITE
PRECHARGE
NOP
NOP
D
IN
n
D
IN
n
+ 1
ACTIVE
tRP
BANK
(
a
or all)
t
WR
BANK
a
,
ROW
DQM
DQ
COMMAND
ADDRESS
BANK
a
,
COL
n
NOP
WRITE
PRECHARGE
NOP
NOP
D
IN
n
D
IN
n
+ 1
ACTIVE
tRP
BANK
(
a
or all)
t
WR
NOTE:
DQM could remain LOW in this example if the WRITE burst is a fixed
length of two.
BANK
a
,
ROW
T6
NOP
NOP
t
WR = 2 CLK (when
t
WR >
t
CK)
t
WR = 1 CLK (
t
CK >
t
WR)
page can be performed to the same bank, as shown in
Figure 16, or each subsequent WRITE may be per-
formed to a different bank.
Data for any WRITE burst may be truncated with a
subsequent READ command, and data for a fixed-
length WRITE burst may be immediately followed by a
READ command. Once the READ command is regis-
tered, the data inputs will be ignored, and WRITEs will
not be executed. An example is shown in Figure 17.
Data
n
+ 1 is either the last of a burst of two or the last
desired of a longer burst.
Data for a fixed-length WRITE burst may be fol-
lowed by, or truncated with, a PRECHARGE command
to the same bank (provided that auto precharge was
not activated), and a full-page WRITE burst may be
truncated with a PRECHARGE command to the same
bank. The PRECHARGE command should be issued
t
WR after the clock edge at which the last desired input
data element is registered. The “two-clock” write-back
requires at least one clock plus time, regardless of fre-
quency, in auto precharge mode. In addition, when
truncating a WRITE burst, the DQM signal must be
used to mask input data for the clock edge prior to, and
the clock edge coincident with, the PRECHARGE com-
mand. An example is shown in Figure 18. Data
n
+ 1 is
either the last of a burst of two or the last desired of a
longer burst. Following the PRECHARGE command, a
subsequent command to the same bank cannot be
issued until
t
RP is met. The precharge will actually be-
gin coincident with the clock-edge (T2 in figure 18) on
an “one clock”
t
WR and sometime between the first
and second clock on an “two clock”
t
WR (between T2
and T3 in Figure 18.)
In the case of a fixed-length burst being executed to
completion, a PRECHARGE command issued at the
optimum time (as described above) provides the same
operation that would result from the same fixed-length
burst with auto precharge. The disadvantage of the
PRECHARGE command is that it requires that the com-
mand and address buses be available at the appropri-
ate time to issue the command; the advantage of the