Intel III 450 MHz 80525PY450512 Data Sheet

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Overshoot/Undershoot is the absolute value of the maximum voltage differential across the input 
buffer relative termination voltage (V

TT

). The overshoot/undershoot guideline limits transitions 

beyond V

TT

 or V

SS

 due to the fast signal edge rates. The processor can be damaged by repeated 

overshoot/undershoot events on 1.5 V or 2.5 V tolerant buffers if the charge is large enough (i.e., if 
the overshoot/undershoot is great enough). Determining the impact of an overshoot/undershoot 
condition requires knowledge of the Magnitude, the Pulse Duration, and the Activity Factor.

When performing simulations to determine impact of overshoot/undershoot, ESD diodes must be 
properly characterized. ESD protection diodes do not act as voltage clamps and will not provide 
overshoot/undershoot protection. ESD diodes modeled within the Intel provided Intel

III Processor I/O Buffer Models do not clamp overshoot/undershoot and will yield correct 
simulation results. If other I/O buffer models are being used to characterize Pentium III processor 
performance, care must be taken to ensure that ESD models do not clamp extreme voltage levels. 
The Intel-provided Pentium

 III Processor I/O Buffer Models also contains I/O capacitance 

characterization. Therefore, removing the ESD diodes from the I/O buffer model will impact 
results and may yield excessive overshoot/undershoot.

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

SS

 (overshoot) and V

TT

 (undershoot). While overshoot can be 

measured relative to V

SS

 using one probe (probe to signal - GND lead to V

SS

), undershoot must be 

measured relative to V

TT

. This could 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 date file analysis:

Converted Undershoot Waveform = V

TT

 – Signal_measured

The Converted Undershoot Waveform appears as a positive (overshoot) signal.

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

After the conversion, the Undershoot/Overshoot Specifications (

 through 

) can be 

applied to the Converted Undershoot Waveform using the same Magnitude and Pulse Duration 
Specifications (

 through 

) as with an overshoot waveform.

Overshoot/undershoot magnitude levels must observe the Absolute Maximum Specifications 
(

 through 

). 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.