User Manual

54 Datasheet

Pentium

III Processor for the PGA370 Socket at 500 MHz to 1.13 GHz

3.4 Non-AGTL+ (Non-AGTL) Signal Quality Specifications and

Measurement Guidelines

There are three signal quality parameters defined for non-AGTL+ signals: overshoot/undershoot,

ringback, and settling limit. All three signal quality parameters are shown in Figure 20 for the non-

AGTL+ signal group.

NOTES:

1. V

= 1.5 V for all non-AGTL+ signals except for BCLK, PICCLK, and PWRGOOD. V

= 2.5 V for BCLK,

PICCLK, and PWRGOOD. BCLK and PICCLK signal quality is detailed in Section 3.1.

3.4.1 Overshoot/Undershoot Guidelines

Overshoot (or undershoot) is the absolute value of the maximum voltage above the nominal high

voltage or below VSS. The overshoot guideline limits transitions beyond VCC or VSS due to the fast

signal edge rates (see Figure 20 for non-AGTL+ signals). The processor can be damaged by

repeated overshoot events on 1.5 V or 2.5 V tolerant buffers if the charge is large enough (i.e., if

the overshoot is great enough). Permanent damage to the processor is the likely result of excessive

overshoot/undershoot. Violating the overshoot/undershoot guideline will also make satisfying the

ringback specification difficult.

The overshoot/undershoot guideline is 0.3 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 1.5 V and 2.5 V

tolerant signals beginning at approximately 0.7 V above the appropriate supply and 0.7 V below

SS. If signals are not reaching the clamping voltage, this will not be 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.

Note: The undershoot guideline limits transitions exactly as described for the ATGL+/AGTL signals. See

Figure 18.

Figure 20. Non-AGTL+ (Non-AGTL) Overshoot/Undershoot, Settling Limit, and Ringback

Undershoot

Overshoot

Settling Limit

Rising-Edge

Ringback

Falling-Edge

Ringback

Time