Kensington Cable Pinouts

The classic Kensington Expert Mouse ("trackball") has long been hailed as one of the greatest technological achievements of the 20th century. To make it work with current technology, however, may require creating a custom cable to convert its proprietary mini-DIN 8 connector to something normal. The Expert Mouse is "dual mode", that is, it can speak as either a serial or PS/2 mouse depending upon the cable used. The table below shows the pinout of the connectors needed to make a cable or verify that one is wired correctly.

Jumper tests

• Cutting jumper J2 is useful! It causes the northwest and northeast button to act as locking toggles for left and right mouse buttons. The first click sends a button press event and the second click releases it. This makes dragging much easier! (Though, how often do you need to drag with the right mouse button?

• Cutting jumper J3 is even more useful! It causes the northwest button to send a middle click and the northeast button acts as a locking toggle for the left mouse button.  

  • If button is locked down via the northeast button, it can also be released by clicking the southwest button.

  • Note that if J2 is also cut, then the northeast button does nothing.

• Cutting jumper J4 does not have any known useful effect. 

  • Cutting J2 as well as J4  causes the mouse to not work at all.

  • Cutting J3 as well as J4 acts the same as if only J3 was cut.

• Connecting J5 (Pin 20 → Vcc) does not appear to do anything. PS/2 and serial work the same as before.
  (Grounding J5 appears to cause only mouse clicks to be sent over serial, but PS/2 works fine.)

• Connecting J6 (Pin 21 → Vcc) causes only mouse clicks to be sent over PS/2 and serial, no mouse movement.
  (Grounding J6 appears to break serial, but PS/2 works.)

• Cutting jumper J7 disables the northwest and northeast buttons. 

Jumper settings are only read when the mouse is first powered on. 

TODO:

• Previous versions of the Expert Mouse documented dip switches that allowed many different things, some of which would be very useful. How do I enable those options?

  • MouseSystems mode

  • More rapid pointer acceleration

  • Left-handed mode

  • Different baud rate

Things that do not work or don't work well

• When button lock is enabled (J2 or J3 cut) and in PS/2 (not serial) mode, if the mouse is unplugged when a button is locked down, it cannot be released by a different mouse device.

• When in 3-button mode (J3 cut) and using the serial port (not PS/2), Kensington's Expert Mouse suffers from the middle-button drag problem. 

  • Microsoft's 3-button serial protocol sends the exact same sequence for middle button down as up. This becomes a problem when dragging with the middle button held down as some events will be missed and the middle button state will end up reversed. 

  • The usual solution to this is to use the "MouseSystems" protocol instead which does not have that misfeature. It is not yet clear at this time how to enable that.

    • Toggling DTR (gpm -o dtr) does not enable MouseSystems.

    • Holding down mouse buttons while plugging in the cable does nothing. (On some mouses, if a button is held down when it gets power it will switch to MouseSystems instead of Microsoft protocol).

    • J4, J5, J6 do not cause the serial port to speak the MouseSystems protocol.

  • Currently the best solution seems to be simply using PS/2 instead of serial.

• The mouse movement speed of the trackball may feel slow on a high-resolution screen. One solution is to apply a transformation matrix only to the trackball (not other mouses) using `xinput` on GNU/Linux.  Here's an example that triples the trackball speed:

  • xinput  set-prop "Generic USB K/B Mouse" "Coordinate Transformation Matrix"  3 0 0  0 3 0  0 0 1

  • To see the possible pointer names, run `xinput` with no arguments.