Vol 1
Electrical Specifications
106 Intel® Xeon® Product 2800/4800/8800 v2 Product Family
Datasheet Volume One, February 2014
6.12 Signal Quality
Data transfer requires the clean reception of data signals and clock signals. Ringing
below receiver thresholds, non-monotonic signal edges, and excessive voltage swings
will adversely affect system timings. Ringback and signal non-monotonicity cannot be
tolerated since these phenomena may inadvertently advance receiver state machines.
Excessive signal swings (overshoot and undershoot) are detrimental to silicon gate
oxide integrity, and can cause device failure if absolute voltage limits are exceeded.
Overshoot and undershoot can also cause timing degradation due to the build up of
inter-symbol interference (ISI) effects.
For these reasons, it is crucial that the designer work towards a solution that provides
acceptable signal quality across all systematic variations encountered in volume
manufacturing.
This section documents signal quality metrics used to derive topology and routing
guidelines through simulation. All specifications are specified at the processor die (pad
measurements).
Specifications for signal quality are for measurements at the processor core only and
are only observable through simulation. Therefore, proper simulation is the only way to
verify proper timing and signal quality.
6.12.1 SMI2 Signal Quality Specifications
Various scenarios for the SMI2 Signals have been simulated to generate a set of layout
guidelines.
Overshoot (or undershoot) is the absolute value of the maximum voltage above or
below V
SS
. The overshoot/undershoot specifications limit transitions beyond specified
maximum voltages or V
SS
due to the fast signal edge rates. The processor can be
damaged by single and/or repeated overshoot or undershoot events on any input,
output, or I/O buffer if the charge is large enough (that is, if the over/undershoot is
great enough). Baseboard designs which meet signal integrity and timing requirements
and which do not exceed the maximum overshoot or undershoot limits listed in
Table 6-29 will insure reliable IO performance for the lifetime of the processor.
Figure 6-24. PWRGOOD Signal Waveform
A
NM_rise
T
NM
V
overshoot
V
IL_MAX
V
undershoot
V
IH_MIN
A
NM_fall
T
NM