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Low Voltage Intel

Xeon

™

Processor at 1.60 GHz, 2.0 GHz and 2.4 GHz

Datasheet 43

3.3 System Bus Signal Quality Specifications

and Measurement Guidelines

3.3.1 Overshoot/Undershoot Guidelines

Overshoot (or undershoot) is the absolute value of the maximum voltage above or below V

. The

overshoot/undershoot specifications limit transitions beyond V

or V

due to the fast signal edge

rates. The processor may be damaged by single and/or repeated overshoot or undershoot events on

any input, output, or I/O buffer when the charge is large enough (i.e., when the over/undershoot is

great enough). Determining the impact of an overshoot/undershoot condition requires knowledge

of the magnitude, the pulse direction, and the activity factor (AF). Permanent damage to the

processor is the likely result of excessive overshoot/undershoot.

When performing simulations to determine impact of overshoot and undershoot, ESD diodes must

be properly characterized. ESD protection diodes do not act as voltage clamps and may not provide

overshoot or undershoot protection. ESD diodes modelled within Intel’s signal integrity models do

not clamp undershoot or overshoot and may yield correct simulation results. When other signal

integrity models are being used to characterize the processor system bus, care must be taken to

Figure 21. High-to-Low System Bus Receiver Ringback Tolerance

for PWRGOOD and TAP Buffer

0.5 * Vcc

Vt+ (min)

Vt- (max)

Vcc

Vss

Vt- (min)

Threshold Region to switch

receiver to a logic 0.

Allowable Ringback

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Lenovo 59P5107 Fiche technique Page 43