Intel III 450 MHz 80525PY450512 Data Sheet

46

Ringback refers to the amount of reflection seen after a signal has switched. The ringback 
specification is the voltage that the signal rings back to after achieving its maximum absolute 
value. (See 

 for an illustration of ringback.) Excessive ringback can cause false signal 

detection or extend the propagation delay. The ringback specification applies to the input pin of 
each receiving agent. Violations of the signal ringback specification are not allowed under any 
circumstances for both AGTL+ and non-AGTL+ signals.

When performing simulations to determine the impact of ringback, ESD diodes must be properly 
characterized. The Intel provided Pentium III Processor I/O Buffer Models contain I/O capacitance 
characterization. Therefore, removing the ESD diodes from the I/O buffer model will impact 
results and may yield incorrect ringback. If other I/O buffer models are being used to characterize 
Pentium III processor performance, care must be taken to ensure that ESD models account for the 
I/O capacitance. See 

 for the signal ringback specifications for both AGTL+ and 

non-AGTL+ signals for simulations at the processor core.

Vss

Undershoot

Magnitude

=   V

TT

 - Signal

Overshoot

Magnitude

=   Signal - Vss

V

TT

2.3V

2.2V
2.1V

2.0V

1.635V

Max

Overshoot
Magnitude

Time Dependent

Overshoot

Converted Undershoot

Waveform

Undershoot

Magnitude

Time Dependent

Undershoot