NT5DS64M8DS
NT5DS32M16DS
512Mb DDR SDRAM
29
REV 1.1 CONSUMER DRAM
Sept. 2013
Writes
Write bursts are initiated with a Write command, as shown in timing figure Write Command on this page.
The starting column and bank addresses are provided with the Write command, and Auto Precharge is either enabled or disabled for
that access. If Auto Precharge is enabled, the row being accessed is precharged at the completion of the burst. For the generic Write
commands used in the following illustrations, Auto Precharge is disabled.
During Write bursts, the first valid data-in element is registered on the first rising edge of DQS following the write command, and
subsequent data elements are registered on successive edges of DQS. The Low state on DQS between the Write command and the
first rising edge is known as the write preamble; the Low state on DQS following the last data-in element is known as the write
postamble. The time between the Write command and the first corresponding rising edge of DQS (tDQSS) is specified with a relatively
wide range (from 75% to 125% of one clock cycle), so most of the Write diagrams that follow are drawn for the two extreme cases (i.e.
tDQSS(min) and tDQSS(max)). Timing figure Write Burst (Burst Length = 4) on page 34 shows the two extremes of tDQSS for a burst of
four. Upon completion of a burst, assuming no other commands have been initiated, the DQs and DQS enters High-Z and any
additional input data is ignored.
Data for any Write burst may be concatenated with or truncated with a subsequent Write command. In either case, a continuous flow of
input data can be maintained. The new Write command can be issued on any positive edge of clock following the previous Write
command. The first data element from the new burst is applied after either the last element of a completed burst or the last desired data
element of a longer burst which is being truncated. The new Write command should be issued x cycles after the first Write command,
where x equals the number of desired data element pairs (pairs are required by the 2n prefetch architecture). Timing figure Write to
Write (Burst Length = 4) on page 35 shows concatenated bursts of 4. An example of nonconsecutive Writes is shown in timing figure
Write to Write: Max DQSS, Non-Consecutive (Burst Length = 4) on page 36. Fullspeed random write accesses within a page or pages
can be performed as shown in timing figure Random Write Cycles (Burst Length = 2, 4 or 8) on page 37. Data for any Write burst may
be followed by a subsequent Read command. To follow a Write without truncating the write burst, tWTR (Write to Read) should be met
as shown in timing figure Write to Read: Non-Interrupting (CAS Latency = 3; Burst Length = 4).
Data for any Write burst may be truncated by a subsequent (interrupting) Read command. This is illustrated in timing figures “Write to
Read: Interrupting (CAS Latency =2; Burst Length = 8)”, “Write to Read: Minimum DQSS, Odd Number of Data (3 bit Write), Interrupting
(CAS Latency = 2; Burst Length = 8)”, and “Write to Read: Nominal DQSS, Interrupting (CAS Latency = 2; Burst Length = 8)”. Note that
only the data-in pairs that are registered prior to the tWTR period are written to the internal array, and any subsequent data-in must be
masked with DM, as shown in the diagrams noted previously.
Data for any Write burst may be followed by a subsequent Precharge command. To follow a Write without truncating the write burst, tWR
should be met as shown in timing figure Write to Precharge: Non-Interrupting (Burst Length = 4).
Data for any Write burst may be truncated by a subsequent Precharge command, as shown in timing figures Write to Precharge:
Interrupting (Burst Length = 4 or 8) on page 43 to Write to Precharge: Nominal DQSS (2 bit Write), Interrupting (Burst Length = 4 or 8).
Note that only the data-in pairs that are registered prior to the tWR period are written to the internal array, and any subsequent data in
should be masked with DM. Following the Precharge command, a subsequent command to the same bank cannot be issued until tRP is
met.
In the case of a Write 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 burst with Auto Precharge. The disadvantage of the Precharge command
is that it requires that the command and address busses be available at the appropriate time to issue the command. The advantage of
the Precharge command is that it can be used to truncate bursts.