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Power Over Ethernet Interoperability Guide by Sanjaya Maniktala

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Timings during 2-Event Classification
As shown in Fig. 4.7, the PSE is required to hold the PI voltage within the class-event range for a specified period called TCLE1 (first class-event duration). TCLE1 can be 6 to 30 ms. This duration is considered enough to allow the PD to turn on its class current sink, and for the PSE to measure it (the class current) accurately. TME1 can be anywhere from 6 to 12 ms. So the maximum duration for 2-event classification, not including TME2, is 30 + 12 + 30 = 72 ms. TME2 must be at least 6 ms, but is left open-ended for reasons explained further below.
In practice, since a Type 2 PSE needs to handle Type 1 cases too with the same chip architecture, TCLE1 usually becomes synonymous with TPDC whenever the PSE ...

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