64Mb: x4, x8, x16 SDRAM
WRITE Operation
Figure 28: WRITE-to-WRITE
T0
T1
T2
CLK
WRITE
NOP
WRITE
Command
Address
DQ
Bank,
Col n
Bank,
Col b
DIN
DIN
DIN
Transitioning data
Don’t Care
1. DQM is LOW. Each WRITE command may be issued to any bank.
Note:
Data for any WRITE burst can be truncated with a subsequent READ command, and
data for a fixed-length WRITE burst can be followed immediately by a READ command.
After the READ command is registered, data input is ignored and WRITEs will not be
executed (see Figure 30 (page 58)). Data n + 1 is either the last of a burst of two or the
last desired data element of a longer burst.
Data for a fixed-length WRITE burst can be followed by or truncated with a PRE-
CHARGE command to the same bank, provided that auto precharge was not activated.
A continuous-page WRITE burst can be truncated with a PRECHARGE command to the
same bank. The PRECHARGE command should be issued tWR after the clock edge at
which the last desired input data element is registered. The auto precharge mode re-
quires a tWR of at least one clock with time to complete, regardless of frequency.
In addition, when truncating a WRITE burst at high clock frequencies (tCK < 15ns), the
DQM signal must be used to mask input data for the clock edge prior to and the clock
edge coincident with the PRECHARGE command (see Figure 31 (page 59)). Data n + 1
is either the last of a burst of two or the last desired data element of a longer burst. Fol-
lowing the PRECHARGE command, a subsequent command to the same bank cannot
be issued until tRP is met.
In the case of a fixed-length burst being executed to completion, a PRECHARGE com-
mand 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 disadvant-
age 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 bursts or continu-
ous page bursts.
PDF: 09005aef80725c0b
64mb_x4x8x16_sdram.pdf - Rev. U 05/13 EN
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57
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