Electronic – PS2 / SMBus communication


I have an OEM touchpad I want to connect to a PC. The drivers for this touchpad are widely available. I asked the manufacturer for the original datasheet, and it says there, that the touchpad interface/protocol is PS2/SMBus.

On the device there is an 8 pin connector – of which 7 pins are used. They are laid out as follows:
Pin assignment

I do know however that a PS/2 connector has only 6 pins (7 incl. the shield, but is it used at all?), and not 8. I can't see how this connector is compatible with PS/2.

FWIW, this is what the spec had to say about interface:



Refer to IBM PS2 specification. Internal pull-up resistors (5k
typical) are provided on DATA and CLOCK lines.

All the commands specified by IBM are implemented, except for the

  • "Scaling" and "Set Resolution" commands generate an "ACK" response from the touchpad, but leave the touchpad resolution unchanged.


Refer to the System Management Bus (SMBus) Specification. Version 2.0.

That's it.

So am I looking here at something that is technically possible?

Best Answer

Your TouchPad is a modular embedded device that offers multiple protocols output. You can either wire the ps/2 pins internally or externally with a ps/2 cable, or wire the SMBUS pins (mainly internal only in practice). If the TouchPad is really nice, it might support both interfaces at the same time, since no pins share functions or overlap.

All pins are broken out to a single 8 pin connector so an OEM laptop builder can wire it as they want. Manufacturer convenience, nothing more.

Newer TouchPad also come with usb interfaces instead of ps/2. Those can be wired to a usb cable the same way.

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