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Re: What bus is the touchpad connected to?

Quoting tom r lopes (tomrlopes@gmail.com):

> Anyways I am continuing my quest to reclaim parts scavenged from old
> laptops.  I have already soldered a USB cable to laptop webcam.  Now
> I'm thinking about the touchpad.
> How would I go about finding out how it is connected? Is it USB? PS/2?
> Or something else?

It's PS/2.

> On my Thinkpad xinput list gives
> Synaptics tm2964-001                      id=12   [slave  pointer  (2)]
> ⎜   ↳ TPPS/2 IBM TrackPoint

Note substring:  'PS/2'.

> From searching the web I find many older touchpads were PS/2 but I am
> wondering if they are USB or maybe I2c now.

That's a concern:  The world does tend to slowly change, but in my
experience in the _past_, such devices have been PS/2 for a long time.
(I obviously cannot preclude the possibility of that suddenly changing.)

> P.S. Also interested in the keyboards.  I understand they are connected to
> the laptop as a raw matrix to controller chip on the board.  So you could
> use a multimeter to get the matrix and Arduino to interface.

On ThinkPads of my past acquantance, the keyboards have always used an
internal PS/2 connection.  (Same necessary disclaimer as above.)

IBM (former maker of ThinkPads) had a perhaps exaggerated love affair
with the PS/2 connector, having invented and pushed for it.  And it was 
quite successful, the sole real problem being that unplugging a
PS/2-attached device with the power on sometimes fries the supporting
motherboard circuitry -- not always, just often enough to create menaces
to your equipment from some wandering idiot deciding to unplug your
peripherals without your permission and, when read the riot act,
protesting that 'I've never seen this do harm'.  So, basically, USB won
over PS/2 primarily by being more idiot-proof.

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