Intel III Xeon 667 MHz 80526KZ667256 Scheda Tecnica

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4.2.2.1 Overshoot/Undershoot Magnitude
Overshoot magnitude describes the maximum potential difference between a signal and its reference voltage level, Vss.
Undershoot Magnitude describes the maximum potential difference between a signal and V

TT

 (undershoot).   While

overshoot can be measured relative to VSS using one probe (probe on signal and ground lead on VSS), Undershoot must
be measured relative to V

TT

.  This can be accomplished by simultaneously measuring the V

TT

 plane while measuring the

signal undershoot.  The true waveform can then be calculated by the oscilloscope itself or by the following oscilloscope
data file analysis:

Converted Undershoot Waveform = V

TT

 - Signal

Note: This Converted Undershoot Waveform appears as a positive (overshoot) signal.

Note:  Overshoot (rising edge) and Undershoot (falling edge) conditions are separate and their impact must be
determined independently.

After the conversion, the Overshoot/Undershoot Specifications can be applied to the Converted Undershoot Waveform
using the Overshoot/Undershoot Magnitude and Pulse Duration Specifications in Table 22.

Overshoot/Undershoot Magnitude levels must also observe the Absolute Maximum Specifications. These specifications
must not be violated at any time regardless of bus activity or system state.  Within these specifications are threshold
levels that define different allowed Pulse Durations.  Provided that the magnitude of the Overshoot/Undershoot is within
the Absolute Maximum Specifications, the impact of the Overshoot/Undershoot Magnitude may be determined based
upon the Pulse Duration and Activity Factor.

4.2.2.2 Overshoot/Undershoot Pulse Duration
Overshoot/Undershoot Pulse Duration describes the total time that an Overshoot/Undershoot event exceeds the
Overshoot/Undershoot Reference Voltage (Vos_ref = 1.635V).  This total time could encompass several oscillations
above the Overshoot/Undershoot Reference Voltage.  Thus, multiple Overshoot/Undershoot pulses within a single
Overshoot/Undershoot event must be measured to determine the total Pulse Duration.

Note: Oscillations below the Reference Voltage cannot be subtracted from the total Overshoot/Undershoot Pulse
Duration.

Note: Multiple Overshoot/Undershoot events occurring within the same clock cycle must be considered together as one
event.  Using the worst-case Overshoot/Undershoot Magnitude, sum together the individual Pulse Durations to determine
the total Overshoot/Undershoot Pulse Duration for that total event.

4.2.2.3 Overshoot/Undershoot Activity Factor
Activity Factor (AF) describes the frequency of Overshoot/Undershoot occurrence relative to a Clock.  Since the highest
frequency of assertion of an AGTL+ or a CMOS signal is every other clock, an AF = 1 indicates that the specific
Overshoot or Undershoot waveform occurs EVERY OTHER clock cycle (e.g., 1-0-1-0… system bus switching pattern).
Thus, an AF = 0.01 indicates that the specific Overshoot or Undershoot waveform occurs 1 time in every 200 CLK cycles.

The specifications provided in Table 22 show the Maximum Pulse Duration allowed for a given Overshoot/Undershoot
Magnitude at a specific Activity Factor.  Each Table entry is independent of all others, meaning that the Pulse Duration
reflects the existence of Overshoot/Undershoot Events of that Magnitude ONLY. A platform with an overshoot/undershoot
that just meets the Pulse Duration for a specific Magnitude where the AF < 1, means that there can be NO other
Overshoot/Undershoot events, even of lesser Magnitude (note that if AF = 1, then the event occurs at all times and no
other events can occur).

Note:  Activity Factor for AGTL+ signals is referenced to BCLK frequency.

Note:  Activity Factor for CMOS signals is referenced to PICCLK frequency.

The overshoot/undershoot specifications listed in the following tables specify the allowable overshoot/undershoot for a
single overshoot/undershoot event. However most systems will have multiple overshoot and/or undershoot events, each
of which will have their own set of parameters (duration, AF and magnitude).   While each overshoot on its own may meet
the overshoot specification, when you add the total impact of all overshoot events, the system may fail.  A guideline to
ensure a system passes the overshoot and undershoot specifications is shown below.

•

 

Insure no signal (CMOS or AGTL+) ever exceed the 1.635V.

•

 

If only one overshoot/undershoot event magnitude occurs, ensure it meets the over/undershoot specifications in the
following tables.  This means that whenever the over/undershoot event occurs, it always over/undershoots to the
same level.