Discharging Port Capacitances and Actual Voltage “Seen” by the PD
As shown in Fig. 4.5, many Type 1 PSEs will complete classification and go straight to power-up without even trying to discharge the port in between the two phases. In Fig. 4.3, we see there are some cases where the port may discharge somewhat after classification. But none of this is specified because there is no “mark-event range” defined for Type 1 PSEs. The mark-event range was introduced in the AT standard only to handle 2-event classifications.
The need to actively discharge the port to some value between the two class events arose simply to distinguish the class events from each other—from the PD’s perspective. So it is important to know not just the PI voltage at the ...

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