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Trying to figure out the pinout of a trackpoint

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delingren:
I came across this keyboard/trackpoint combo from a ThinkPad X1 Carbon Gen 1. I'm trying to figure out the pinout. The keyboard should be pretty easy. I've done it for a few other keyboards. The trackpoint should be a PS2 device, I suppose. But I need to first figure out the pinout. I did check out https://deskthority.net/wiki/TrackPoint_Hardware but my module is not listed there.

It has 10 pins. I suppose 3 are for the buttons. Then there's Vcc, GND, DATA, and CLK, maybe a RESET as well. The remaining 2 are probably NC. I came across this post https://geekhack.org/index.php?topic=115912.0 and its original version in Chinese (I speak Chinese), which is very helpful. The markings on the chip on my controller don't indicate it's TPM754 though. It reads PSC4L7. I wasn't able to find any info on it. It looks suspiciously like a TPM754 with 28 pins. But I can't be certain.

I wonder if anyone has ever come across this trackpoint and can shed some light? Thanks.

bigmac223:
Buzz out the continuity between the TPM754 to the pins you wish to identify.  Refer to the reference schematic found on the TPM754 datasheet.  Your red circled part is most likely a resonator (X1 on the reference schematic).  A resonator is a lower cost version of a crystal and provides the clock source for the microcontroller.

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