AS4C256M16D3
Read Timing; Clock to Data Strobe relationship
Clock to Data Strobe relationship is shown in the following figure and is applied when the DLL is enabled and
locked.
Rising data strobe edge parameters:
tDQSCK min/max describes the allowed range for a rising data strobe edge relative to CK and CK#. tDQSCK
is the actual position of a rising strobe edge relative to CK and CK#. tQSH describes the data strobe high
pulse width.
Falling data strobe edge parameters:
tQSL describes the data strobe low pulse width.
Figure 19. Clock to Data Strobe relationship
RL Measured
to this point
CLK#
CLK
tDQSCK (min)
tDQSCK (min)
tQSL
tQSH
tDQSCK (min)
tQSL
tDQSCK (min)
tQSL
tHZ(DQS) (min)
tLZ(DQS) min
tQSH
tQSH
DQS, DQS#
Early Strobe
tRPRE
tLZ(DQS) max
tRPST
tHZ(DQS) (max)
tRPST
Bit 0
Bit 1
tDQSCK (max)
Bit 2
Bit 3
tDQSCK (max)
Bit 4
Bit 5
tDQSCK (max)
Bit 6
Bit 7
tDQSCK (max)
DQS, DQS#
Late Strobe
tRPRE
tQSH
tQSL
tQSH
tQSL
tQSH
tQSL
Bit 0
Bit 1
Bit 2
Bit 3
Bit 4
Bit 5
Bit 6
Bit 7
NOTES:
1. Within a burst, rising strobe edge is not necessarily fixed to be always at tDQSCK(min) or tDQSCK(max). Instead, rising strobe
edge can vary between tDQSCK(min) and tDQSCK(max).
2. Notwithstanding note 1, a rising strobe edge with tDQSCK(max) at T(n) can not be immediately followed by a rising strobe edge
with tDQSCK(min) at T(n+1). This is because other timing relationships (tQSH, tQSL) exist: if tDQSCK(n+1) < 0: tDQSCK(n) < 1.0 tCK -
(tQSHmin + tQSLmin) - | tDQSCK(n+1) |
3. The DQS, DQS# differential output high time is defined by tQSH and the DQS, DQS# differential output low time is defined by tQSL.
4. Likewise, tLZ(DQS)min and tHZ(DQS)min are not tied to tDQSCKmin (early strobe case) and tLZ(DQS)max and tHZ(DQS)max are
not tied to tDQSCKmax (late strobe case).
5. The minimum pulse width of read preamble is defined by tRPRE(min).
6. The maximum read postamble is bound by tDQSCK(min) plus tQSH(min) on the left side and tHZDSQ(max) on the right side.
7. The minimum pulse width of read postamble is defined by tRPST(min).
8. The maximum read preamble is bound by tLZDQS(min) on the left side and tDQSCK(max) on the right side.
Confidential
43
Rev. 3.0
Aug. /2014
ALSC [ ALLIANCE SEMICONDUCTOR CORPORATION ]
