IBM0612404GT3B
IBM0612804GT3B
128Mb Double Data Rate Synchronous DRAM
Advance Rev 0.2
Writes
Write bursts are initiated with a Write command, as shown in timing figure Write Command on page 31.
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 Pre-
charge 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 com-
mand and the first corresponding rising edge of DQS (t
) is specified with a relatively wide range (from
DQSS
75% to 125% of one clock cycle), so most of the Write diagrams that follow are drawn for the two extreme
cases (i.e. t (min) and t (max)). Timing figure Write Burst (Burst Length = 4) on page 32 shows the
DQSS
DQSS
two extremes of t
for a burst of four. Upon completion of a burst, assuming no other commands have
DQSS
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 pos-
itive 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 33 shows concatenated bursts of 4. An example of non-con-
secutive Writes is shown in timing figure Write to Write: Max DQSS, Non-Consecutive (Burst Length = 4) on
page 34. Full-speed random write accesses within a page or pages can be performed as shown in timing fig-
ure Random Write Cycles (Burst Length = 2, 4 or 8) on page 35. Data for any Write burst may be followed by
a subsequent Read command. To follow a Write without truncating the write burst, t
(Write to Read)
WTR
should be met as shown in timing figure Write to Read: Non-Interrupting (CAS Latency = 2; Burst Length = 4)
on page 36.
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
D
, Odd Number of Data (3 bit Write), Interrupting (CAS Latency = 2; Burst Length = 8)”, and “Write to
QSS
Read: Nominal D
, Interrupting (CAS Latency = 2; Burst Length = 8)”. Note that only the data-in pairs that
QSS
are registered prior to the t
period are written to the internal array, and any subsequent data-in must be
WTR
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, t
should be met as shown in timing figure Write to Precharge: Non-Interrupting
WR
(Burst Length = 4) on page 40.
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 41 to Write to Precharge: Nominal DQSS (2
bit Write), Interrupting (Burst Length = 4 or 8) on page 43. Note that only the data-in pairs that are registered
prior to the t
period are written to the internal array, and any subsequent data in should be masked with
WR
DM. Following the Precharge command, a subsequent command to the same bank cannot be issued until t
is met.
RP
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 Pre-
charge. The disadvantage of the Precharge command is that it requires that the command and address bus-
ses 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.
©IBM Corporation. All rights reserved.
Use is further subject to the provisions at the end of this document.
06K0566.F39350
5/00
Page 30 of 79
IBM [ IBM ]
