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From: Sylvia Else <sylvia@email.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Wake on USB event
Date: Sat, 1 Feb 2025 16:22:21 +0800
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On 01-Feb-25 8:36 am, Don Y wrote:
> On 1/31/2025 9:22 AM, Sylvia Else wrote:
>>> It also seems like Windows only leaves USB ports powered up
>>> during sleep *if* they were active while the machine was awake (?).
>>
>> It appears to me that the device drives a 'K' state onto the data 
>> lines for between 1 and 15ms. The 'K' state is the opposite of the 
>> idle state.
> 
> Said another way, does the exchange contain "data" (a keystroke) or
> is it purely for notification?

If I appear to be double posting, it's because some of my postings seem 
to be vanishing.

On my reading of the spec, it just swaps the data line levels for a 
period, and then swaps them back. I wouldn't expect any data transfer, 
because USB devices do not spontaneously send data, they respond only 
when polled.

I suspect it's going to come down to the voltage levels on the data+ and 
data- lines. Data+ should stay high (above 3V), and data- should stay 
low. Time to build that USB breakout box.

Sylvia.