1Gb: x4, x8, x16 DDR2 SDRAM
18. The inputs to the DRAM must be aligned to the associated clock, that is, the actual clock
that latches it in. However, the input timing (in ns) references to the tCK (AVG) when
determining the required number of clocks. The following input parameters are deter-
mined by taking the specified percentage times the tCK (AVG) rather than tCK: tIPW,
tDIPW, tDQSS, tDQSH, tDQSL, tDSS, tDSH, tWPST, and tWPRE.
19. The DRAM output timing is aligned to the nominal or average clock. Most output param-
eters must be derated by the actual jitter error when input clock jitter is present; this
will result in each parameter becoming larger. The following parameters are required to
be derated by subtracting tERR5per (MAX): tAC (MIN), tDQSCK (MIN), tLZDQS (MIN), tLZDQ
(MIN), tAON (MIN); while the following parameters are required to be derated by sub-
tracting tERR5per (MIN): tAC (MAX), tDQSCK (MAX), tHZ (MAX), tLZDQS (MAX), tLZDQ
(MAX), tAON (MAX). The parameter tRPRE (MIN) is derated by subtracting tJITper (MAX),
while tRPRE (MAX), is derated by subtracting tJITper (MIN). The parameter tRPST (MIN) is
derated by subtracting tJITdty (MAX), while tRPST (MAX), is derated by subtracting tJITd-
ty (MIN). Output timings that require tERR5per derating can be observed to have offsets
relative to the clock; however, the total window will not degrade.
20. When DQS is used single-ended, the minimum limit is reduced by 100ps.
21. tHZ and tLZ transitions occur in the same access time windows as valid data transitions.
These parameters are not referenced to a specific voltage level, but specify when the
device output is no longer driving (tHZ) or begins driving (tLZ).
22. tLZ (MIN) will prevail over a tDQSCK (MIN) + tRPRE (MAX) condition.
23. This is not a device limit. The device will operate with a negative value, but system per-
formance could be degraded due to bus turnaround.
24. It is recommended that DQS be valid (HIGH or LOW) on or before the WRITE command.
The case shown (DQS going from High-Z to logic LOW) applies when no WRITEs were
previously in progress on the bus. If a previous WRITE was in progress, DQS could be
HIGH during this time, depending on tDQSS.
25. The intent of the “Don’t Care” state after completion of the postamble is that the DQS-
driven signal should either be HIGH, LOW, or High-Z, and that any signal transition
within the input switching region must follow valid input requirements. That is, if DQS
transitions HIGH (above VIH[DC]min), then it must not transition LOW (below VIH[DC]) prior
to tDQSH (MIN).
26. Referenced to each output group: x4 = DQS with DQ0–DQ3; x8 = DQS with DQ0–DQ7;
x16 = LDQS with DQ0–DQ7; and UDQS with DQ8–DQ15.
27. The data valid window is derived by achieving other specifications: tHP (tCK/2), tDQSQ,
and tQH (tQH = tHP - tQHS). The data valid window derates in direct proportion to the
clock duty cycle and a practical data valid window can be derived.
28. tQH = tHP - tQHS; the worst case tQH would be the lesser of tCL (ABS) MAX or
tCH (ABS) MAX times tCK (ABS) MIN - tQHS. Minimizing the amount of tCH (AVG) offset
and value of tJITdty will provide a larger tQH, which in turn will provide a larger valid
data out window.
29. This maximum value is derived from the referenced test load. tHZ (MAX) will prevail
over tDQSCK (MAX) + tRPST (MAX) condition.
30. The values listed are for the differential DQS strobe (DQS and DQS#) with a differential
slew rate of 2 V/ns (1 V/ns for each signal). There are two sets of values listed: tDSa, tDHa
and tDSb, tDHb. The tDSa, tDHa values (for reference only) are equivalent to the baseline
values of tDSb, tDHb at VREF when the slew rate is 2 V/ns, differentially. The baseline val-
ues, tDSb, tDHb, are the JEDEC-defined values, referenced from the logic trip points. tDSb
is referenced from VIH(AC) for a rising signal and VIL(AC) for a falling signal, while tDHb is
referenced from VIL(DC) for a rising signal and VIH(DC) for a falling signal. If the differen-
tial DQS slew rate is not equal to 2 V/ns, then the baseline values must be derated by
adding the values from Table 30 (page 60) and Table 31 (page 61). If the DQS differ-
ential strobe feature is not enabled, then the DQS strobe is single-ended and the
baseline values must be derated using Table 32 (page 62). Single-ended DQS data tim-
ing is referenced at DQS crossing VREF. The correct timing values for a single-ended DQS
PDF: 09005aef821ae8bf
1GbDDR2.pdf – Rev. T 02/10 EN
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