AS4C64M8D2
NOTE 4: Differential data strobe
DDR2 SDRAM pin timings are specified for either single ended mode or differential mode depending on the
setting of the EMRS “Enable DQS” mode bit; timing advantages of differential mode are realized in system design.
The method by which the DDR2 SDRAM pin timings are measured is mode dependent. In single ended mode,
timing relationships are measured relative to the rising or falling edges of DQS crossing at VREF. In differential
mode, these timing relationships are measured relative to the crosspoint of DQS and its complement, DQS#. This
distinction in timing methods is guaranteed by design and characterization. Note that when differential data strobe
mode is disabled via the EMRS, the complementary pin, DQS#, must be tied externally to VSS through a 20 Ω to
10 kΩ resistor to insure proper operation
NOTE 5: AC timings are for linear signal transitions.
NOTE 6:All voltages are referenced to VSS.
NOTE 7:These parameters guarantee device behavior, but they are not necessarily tested on each device. They
may be guaranteed by device design or tester correlation
NOTE 8: Tests for AC timing, IDD, and electrical (AC and DC) characteristics, may be conducted at nominal
reference/supply voltage levels, but the related specifications and device operation are guaranteed for the full
voltage range specified.
Specific notes for dedicated AC parameters
NOTE 1:User can choose which active power down exit timing to use via MRS (bit 12). tXARD is expected to be used
for fast active power down exit timing. tXARDS is expected to be used for slow active power down exit timing
where a lower power value is defined by each vendor data sheet.
NOTE 2: AL=Additive Latency.
NOTE 3:This is a minimum requirement. Minimum read to precharge timing is AL+BL/2 provided that the tRTP and
tRAS (min) have been satisfied.
NOTE 4: A minimum of two clocks (2* tCK) is required irrespective of operating frequency.
NOTE 5: Timings are specified with command/address input slew rate of 1.0 V/ns.
NOTE 6:Timings are specified with DQs, DM, and DQS’s (DQS in single ended mode) input slew rate of 1.0V/ns.
NOTE 7:Timings are specified with CK/CK# differential slew rate of 2.0 V/ns. Timings are guaranteed for DQS
signals with a differential slew rate of 2.0 V/ns in differential strobe mode and a slew rate of 1 V/ns in single
ended mode.
NOTE 8:Data setup and hold time derating.
For all input signals the total tDS (setup time) and tDH (hold time) required is calculated by adding the data sheet.
tDS(base) and tDH(base) value to the ΔtDS and ΔtDH derating value respectively.
Example: tDS (total setup time) =tDS (base) + ΔtDS.For slew rates in between the values listed in Tables 26, the
derating values may obtained by linear interpolation.These values are typically not subject to production test.
They are verified by design and characterization.
Table 26. DDR2-667/800 tDS/tDH derating with differential data strobe
△tDS, △tDH derating values for DDR2-667, DD2-800 (All units in ‘ps’; the note applies to the entire table)
DQS,DQS# Differential Slew Rate
2.8 V/ns
2.4 V/ns
2.0 V/ns
1.8 V/ns
1.6 V/ns
1.4 V/ns
1.2 V/ns
1.0 V/ns
0.8 V/ns
△tDS
△tDH
△tDS
△tDH
△tDS
△tDH
△tDS
△tDH
△tDS
△tDH
△tDS
△tDH
△tDS
△tDH
△tDS
△tDH
△tDS
△tDH
DQ
2.0
1.5
1.0
0.9
0.8
0.7
0.6
0.5
0.4
100
63
42
0
-
100
63
100
67
0
63
42
0
-
-
-
-
-
-
-
-
-
-
-
-
Slew
Rate
V/ns
67
0
-
67
0
-5
-
42
79
12
7
54
12
-2
-19
-42
-
-
24
19
11
2
-
24
10
-7
-30
-59
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
0
-
-
-14
-5
-13
-
-14
-31
-
31
23
14
2
22
5
-
-
-
-
-
-
-
-
-
-
-
-
-1
-10
-
35
26
14
-12
-52
17
-6
-
-
-
-
-
-
-
-18
-47
-89
-
38
26
0
6
-
-
-
-
-
-
-
-10
-
-35
-77
-140
-23
-65
-128
38
12
-28
-11
-53
-116
-
-
-
-
-
-
-
-24
-
-
-
-
-
-
-
-
-
-
-40
Confidential
28
Rev. 1.0
Feb. /2014
ALSC [ ALLIANCE SEMICONDUCTOR CORPORATION ]
