Xilinx Virtex-5 FPGA ML561 - Manual (Page 92)

92 www.xilinx.com Virtex-5 FPGA ML561 User Guide
UG199 (v1.2.1) June 15, 2009
Chapter 7: ML561 Hardware-Simulation Correlation R
Table 7-16 summarizes the extrapolated SI characteristics of all six test signals.
Here are some observations about extrapolated SI characteristics among these test signals:
•
The Data Valid Window (DVW) values already account for the degradation caused by
ISI due to the PRBS6 test pattern. For timing analysis, two values need to be taken into
consideration appropriately. For a PRBS6 test pattern, the worst-case DVW value
(after discounting for ISI) is 82% UI for DDR2 DIMM operations.
•
DDR2 write operations, as compared to QDRII write operations, have a lower noise
margin due to the always on nature of the DCI termination on the DQ signal for the
SSTL18_II_DCI I/O standard at the FPGA. Consequently, the overshoot/undershoot
margin for DDR2 write operations is higher than for QDRII write operations. The
DDR2 DIMM write operation has the lowest VIL noise margin of 107 mV.
•
For read operations, the sum of VIH and VIL noise margins beyond the AC value
specifications is at least 509 mV (56.6% of VREF). QDRII read operations have the
lowest VIL noise margin of 201 mV.
• All six signals have positive values for overshoot and undershoot margins. QDRII
write operations have the lowest undershoot margin value of 30 mV.
(For Table 5-1, page 48 through Table 5-5, page 49 , the recommendations remain the same
except for a clarification for DDR2 ODT as “75 ohm ODT”.)
Table 7-16: Summary of Worst-Case SI Characteristics
Operation
ΔDVW
(% UI)
ΔISI
(% UI)
Noise Margin
(% VREF)
Overshoot /
Undershoot Margin
(% VREF)
DDR2 Component Write
1.27 ns
(84%)
127 ps
(8.5%)
570 mV
(63.3%)
685 mV
(76.1%)
DDR2 Component Read
1.29 ns
(86%)
178 ps
(11.9%)
867 mV
(96.3%)
349 mV
(38.9%)
DDR2 DIMM Write
1.23 ns
(82%)
117 ps
(7.8%)
253 mV
(28.1%)
981 mV
(109.0%)
DDR2 DIMM Read
1.23 ns
(82%)
224 ps
(14.9%)
546 mV
(60.7%)
989 mV
(109.9%)
QDRII Write
1.38 ns
(83%)
313 ps
(18.8%)
687 mV
(76.3%)
186 mV
(20.7%)
QDRII Read
1.45 ns
(87%)
85 ps
(5.1%)
509 mV
(56.5%)
1183 mV
(131.5%)