Zynq-7000 AP SoC and 7 Series FPGAs MIS v4.1
152
UG586 November 30, 2016
Chapter 1:
DDR3 and DDR2 SDRAM Memory Interface Solution
During the centering substage the write
DQS
is centered in the write
DQ
window based on
the edges found during the edge detection stage. At the end of this stage, write
DQS
should
be centered in the write
DQ
window.
DQS
to
CK
are not correct therefore write leveling is
performed at the end of this stage of calibration.
With every stage 3 tap decrease, the stage 2 taps are increased by 2 to maintain the
DQS
to
CK
relationship established during write leveling. Similarly, with every stage 3 tap
increment, the stage 2 taps are decreased by 2. If stage 2 taps reach 0 or 63, stage 3 tap
increment/decrement is allowed to proceed up to the left and right limit values to avoid
t
DQSS
violation. At the end of this stage of calibration, write leveling is redone to align
DQS
and
CK
using stage 2 taps.
Write Calibration
Write calibration is performed after both stages of read leveling because correct data
pattern sequence detection is necessary for this stage of calibration. Write calibration is
required to align
DQS
to the correct
CK
edge. During write leveling,
DQS
is aligned to the
nearest rising edge of
CK
. However, this might not be the edge that captures the write
command. Depending on the interface type (UDIMM, RDIMM, or component), the
DQS
could either be one
CK
cycle earlier than, one
CK
cycle later than, or aligned to the
CK
edge
that captures the write command.
shows several different scenarios based on
the initial phase relationship between
DQS
and
CK
for a UDIMM or RDIMM interface.
Case 3
Found
Not
Found
Not
Found
Not
Found
(fuz lim2ocal_stg3_right_lim)/2
Case 4
Not
Found
Found
Not
Found
Not
Found
(lim2ocal_stg3_le zero2fuzz)/2
Noise/Jitter Region
Case 1
Found
Found
Found
Not
Found
(fuz zero2fuzz)/2
Case 2
Not
Found
Found
Found
Found
(zer fuzz2oneeighty)/2 – 90
o
Case 3
Not
Found
Found
Found
Not
Found
(zer fuzz2oneeighty)/2 – 90
o
Fall Window 180
o
to 225
o
Case 1
Not
Found
Found
Found
Found
(zer fuzz2oneeighty)/2 – 90
o
Case 2
Not
Found
Not
Found
Found
Found
(fuzz2one oneeighty2fuzz)/2 – 180
o
Case 3
Not
Found
Not
Found
Found
Not
Found
(fuzz2one lim2ocal_stg3_right_lim)/2 – 180
o
Table 1-60:
Starting Scenarios for Write DQS
(Cont’d)
Start DQS
f2z
z2f
f2o
o2f
Center Equation