Zynq-7000 AP SoC and 7 Series FPGAs MIS v4.1
450
UG586 November 30, 2016
Chapter 3:
RLDRAM II and RLDRAM 3 Memory Interface Solutions
For frequencies < 400 MHz, because FREQ_REF_CLK has twice the frequency of
MEM_REF_CLK, the maximum delay that can be derived from the PHASER is 1/2 the data
period or 1/4 the clock period. Hence for frequencies < 400 MHz, just using the PHASER
delay taps might not be sufficient to accurately center the clock in the data window. For
these frequency ranges, a combination of both data delay using IDELAY taps and PHASER
taps is used. The calibration logic determines the best possible delays, based on the initial
clock-data alignment. The algorithm first delays the read capture clock using the
PHASER_IN fine delay line until a data window edge is detected.
X-Ref Target - Figure 3-53
Figure 3-53:
Read Level Stage 1
Rise
DQ
Fall
QK
(1) Initial
Alignment
Rise
DQ
Fall
(2) Data
pushed with
IDELAY to
edge align
Fall
Data Shift
QK
DQ
Rise
Fall
Fall
First edge
QK
DQ
Rise
Fall
Fall
Second
edge
QK
DQ
Rise
Fall
Fall
Calculated center
(3) Push Qk
clock, find
edge where
data goes
“valid/
invalid”
(4) Push Qk
clock, find
second edge
where data
goes “valid/
invalid”
(5) Compute
center and
move QK
QK Shift
QK Shift