80546KF Datasheet, PDF (56/138 Pages) Intel Corporation – 64-bit Intel Xeon Processor MP with up to 8MB L3 Cache

Front Side Bus Signal Quality Specifications
Figure 3-4. High-to-Low Receiver Ringback Tolerance for PWRGOOD and TAP Signals
V_TT
Vt+ (min)
0.5 * V_TT
Vt- (max)
Vt- (min)
Allowable Ringback
Threshold Region to switch
receiver to a logic 0.
3.1.2
3.1.3
Vss
Overshoot/Undershoot Guidelines
Overshoot (or undershoot) is the absolute value of the maximum voltage above or below V_SS. The
overshoot/undershoot specifications limit transitions beyond V_TT 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 (i.e., if the over/undershoot is great
enough). Determining the impact of an overshoot/undershoot condition requires knowledge of the
magnitude, the pulse duration, and the activity factor (AF). Permanent damage to the processor is
the likely result of excessive overshoot/undershoot.
When performing simulations to determine the impact of overshoot and undershoot effects, ESD
diodes must be properly characterized. ESD protection diodes do not act as voltage clamps and will
not provide overshoot or undershoot protection. ESD diodes modeled within Intel signal integrity
models do not clamp undershoot or overshoot and will yield correct simulation results. If other
signal integrity models are being used to characterize the processor front side bus, care must be
taken to ensure that ESD models do not clamp extreme voltage levels. Intel signal integrity models
also contain I/O capacitance characterization. Therefore, removing the ESD diodes from a signal
integrity model will impact results and may yield excessive overshoot/undershoot.
Overshoot/Undershoot Magnitude
Magnitude describes the maximum potential difference between a signal and its voltage reference
level. For the processor, both are referenced to V_SS. It is important to note that overshoot and
undershoot conditions are separate and their impact must be determined independently.
The pulse magnitude, duration, and activity factor must all be used to determine if the overshoot/
undershoot pulse is within specifications.
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64-bit Intel^® Xeon™ Processor MP with up to 8MB L3 Cache Datasheet