SDRAM
AS4SD2M32
Austin Semiconductor, Inc.
clock edge coincident with, the PRECHARGE command. 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 tRP is met. The precharge can be
issued coincident with the first coincident clock edge (T2 in
Figure 18) on an A1 Version and with the second clock on an
A2 Version (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 is 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.
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 registered, 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 followed 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 com-
mand 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 requires a
tWR of at least one clock plus time, regardless of frequency. 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
FIGURE 16: Random WRITE Cycles
FIGURE 18: WRITE to PRECHARGE
FIGURE 17: WRITE to READ
Austin Semiconductor, Inc. reserves the right to change products or specifications without notice.
AS4SD2M32
Rev. 1.0 1/08
17
AUSTIN [ AUSTIN SEMICONDUCTOR ]
