Intel® Celeron® Processor for PGA370 up to 1.40 GHz on 0.13 µ Process
3.2.2
Overshoot/Undershoot Magnitude
Magnitude describes the maximum potential difference between a signal and its voltage reference
level, VSS (overshoot) and VTT (undershoot). While overshoot can be measured relative to VSS
using one probe (probe to signal and GND lead to VSS), undershoot must be measured relative to
VTT. This could be accomplished by simultaneously measuring the VTT plane while measuring the
signal undershoot. Today’s oscilloscopes can easily calculate the true undershoot waveform. The
true undershoot waveform can also be obtained with the following oscilloscope data file analysis:
Converted Undershoot Waveform = VTT - Signal_measured
Note: The 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 true waveform conversion, the undershoot/overshoot specifications shown in Table 26
through Table 29 can be applied to the converted undershoot waveform using the same magnitude
and pulse duration specifications used with an overshoot waveform.
Overshoot/undershoot magnitude levels must observe the Absolute Maximum Specifications listed
in Table 26 through Table 29. 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 (1.78 V AGTL, 2.08 V CMOS), the pulse magnitude, duration
and activity factor must all be used to determine if the overshoot/undershoot pulse is within
specifications.
3.2.3
Overshoot/Undershoot Pulse Duration
Pulse duration describes the total time an overshoot/undershoot event exceeds the overshoot/
undershoot reference voltage (Vos_ref = 1.32 V AGTL, 1.80 V CMOS). The total time could
encompass several oscillations above the reference voltage. Multiple overshoot/undershoot pulses
within a single overshoot/undershoot event may need to be measured to determine the total pulse
duration.
Note: Oscillations below the reference voltage can not 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.
3.2.4
Activity Factor
Activity Factor (AF) describes the frequency of overshoot (or 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. Thus, an AF = 0.01 indicates that the specific overshoot (or undershoot) waveform
occurs one time in every 200 clock cycles.
The specifications provided in Table 26 through Table 29 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
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Datasheet
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