Specifications

PENTIUM® PRO PROCESSOR AT 150, 166, 180, and 200 MHz E
58
TX out 0 jim 0 Z0=40 TD=12.25PS
ty jim 0 in 0 Z0=66 TD=12.25ps
.ENDS
5.0 3.3 V Tolerant Signal Quality
Specifications
The signals that are 3.3 V tolerant should also meet
signal quality specifications to guarantee that the
components read data properly and to ensure that
incoming signals do not affect the long term reliability
of the component. There are three signal quality
parameters defined for the 3.3 V tolerant signals.
They are Overshoot/Undershoot, Ringback and
Settling Limit. All three signal quality parameters are
shown in Figure 37. The
Pentium® Pro Processor
I/O Buffer Models—IBIS Format (On world wide web
page http://www.intel.com)
contain models for
simulating 3.3 V tolerant signal distribution.
5.1. OVERSHOOT/UNDERSHOOT
GUIDELINES
Overshoot (or undershoot) is the absolute value of
the maximum voltage allowed above the nominal
high voltage or below VSS. The
overshoot/undershoot guideline limits transitions
beyond V
CC
P or V
SS
due to the fast signal edge
rates. See Figure 37. The processor can be
damaged by repeated overshoot events on 3.3 V
tolerant buffers if the charge is large enough (i.e. if
the overshoot is great enough). However, excessive
ringback is the dominant harmful effect resulting from
overshoot or undershoot (i.e. violating the
overshoot/undershoot guideline will make satisfying
the ringback specification difficult). The
overshoot/undershoot guideline is 0.8 V and
assumes the absence of diodes on the input. These
guidelines should be verified in simulations without
the on-chip ESD protection diodes present
because the diodes will begin clamping the 3.3 V
tolerant signals beginning at approximately 1.5 V
above V
CC
P and 0.5 V below VSS. If signals are not
reaching the clamping voltage, then this is not an
issue. A system should not rely on the diodes for
overshoot/undershoot protection as this will
negatively affect the life of the components and make
meeting the ringback specification very difficult.