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64MSDRAM_2.fm - Rev. N 12/08 EN
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2000 Micron Technology, Inc. All rights reserved.
64Mb: x4, x8, x16 SDRAM
Commands
A fixed-length READ burst may be followed by, or truncated with, a PRECHARGE
command to the same bank (provided that auto precharge was not activated), and a full-
page burst may be truncated with a PRECHARGE command to the same bank. The
PRECHARGE command should be issued x cycles before the clock edge at which the last
desired data element is valid, where x = CL -1. This is shown in
Figure 16 for each
possible CL; data element n + 3 is either the last of a burst of four or the last desired of a
longer burst. Following the PRECHARGE command, a subsequent command to the
same bank cannot be issued until tRP is met. Note that part of the row precharge time is
hidden during the access of the last data element(s).
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 disadvan-
tage of the PRECHARGE command is that it requires that the command and address
buses be available at the appropriate time to issue the command; the advantage of the
PRECHARGE command is that it can be used to truncate fixed-length or full-page bursts.
Full-page READ bursts can be truncated with the BURST TERMINATE command, and
fixed-length READ bursts may be truncated with a BURST TERMINATE command,
provided that auto precharge was not activated. The BURST TERMINATE command
should be issued x cycles before the clock edge at which the last desired data element is
element n + 3 is the last desired data element of a longer burst.
Figure 16:
READ-to-PRECHARGE
Note:
DQM is LOW.
CLK
DQ
DOUT
n
T2
T1
T4
T3
T6
T5
T0
COMMAND
ADDRESS
READ
NOP
BANK,
COL n
NOP
DOUT
n + 1
DOUT
n + 2
DOUT
n + 3
PRECHARGE
NOP
T7
DON’T CARE
CLK
DQ
DOUT
n
T2
T1
T4
T3
T6
T5
T0
COMMAND
ADDRESS
READ
NOP
BANK,
COL n
NOP
DOUT
n + 1
DOUT
n + 2
DOUT
n + 3
PRECHARGE
NOP
X = 1 cycle
CL = 2
CL = 3
X = 2 cycles
TRANSITIONING DATA