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From: Dan Purgert <dan@djph.net>
Newsgroups: sci.electronics.repair
Subject: Re: Re (2): USB functionality.
Date: Tue, 12 Mar 2024 19:27:04 -0000 (UTC)
Organization: A noiseless patient Spider
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On 2024-03-12, Roger Hayter wrote:
> On 12 Mar 2024 at 16:29:31 GMT, "peter@easthope.ca" <peter@easthope.ca> wrote:
>
>> In article <2219572717.2fe80b82@uninhabited.net>, Roger Hayter
>> <roger@hayter.org> wrote:
>>> But can even USB-C accept a signal input (keyboard and mouse for
>>> instance) and unrelated signal output (audio for instance) on the
>>> same physical socket? I ask only out of curiosity.
>> 
>> The setup is rarely tried.  Appears that nobody can reply.
>> 
>> A keyboard or mouse sends tiny amounts of data; a few bytes per
>> second. In principle the link should be able to fit that in without
>> significant drop-outs in audio output.  WIth so many details involved,
>> a general answer is difficult. When all else fails, we can test and
>> see what happens.  =8~)
>> 
>> Regards,             ... P.
>
> So you could use an overarching protocol which was bilateral (ethernet
> anyone?) and send and separate messages both ways.  What I was aksing was
> whether within the USB protocol there was provision for using some pins in for
> one electrical signal (bi or uni-directional) and other pins for another
> electrical signal. Because that would be the only way to do it without special
> software on at least one of the devices.
>

There's only one set of pins (well, two sets if you count USB2 / USB3 --
but you can only use one set at a time).  

USB2 -> D+/D- (Bi-directional / Half Duplex)
USB3 -> TX1+/TX1- and RX2+/RX2- (optionally Full Duplex, IIRC)

As I recall the "Tx" pair is "Host Transmit to Peripheral", and "Rx" is
"Host Receive from Peripheral", but it's been a while since I read up on
the USB3 / USB-C implementations.

-- 
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