Documenting interesting *new* M13 Controller

[SunshineRag_DT]

I have had a Lexmark branded M13 for a while now but have not really used it because the cable was deteriorating and DIN and Serial connections and the usage of the FSR Track Pointer. But now that I am trying to do some mods to it I have cracked it open. After looking online it seems there are no pictures or uses of this specific controller on the internet, so that is why I stated this is "new" as in undocumented. Maybe my Google-Fu is weak, but just in case I wanted to post some pictures and some interesting findings I have made to document for posterity.

Here it is:

1403380_M13_Controller.jpg (1.14 MiB) Viewed 2785 times

On the surface it looks like any other pre 1998 Model M controller. But thanks to the nice folks at clickykeyboards.com I have an IBM Branded M13 controller to compare it to. This other one came from a M13 P/N: 92G7461 keyboard, build within 3 months at the same Lexmark factory.

Once you put them side by several interesting things stand out:

1403380_M13_Controller_Compare.jpg (2.26 MiB) Viewed 2785 times

Looking at this picture the left side of both boards is the keyboard controller and computer connection, and the right side is the pointing controller electronics. First thing to note is the Trackpoint controller has many more components. In fact, it includes 3 more ICs (circled in yellow) than the FSR controller probably due to the Trackpoint, but there are also more resistors and caps for these connections. Overall this is probably why the M13 Trackpoints have such a power draw, in fact they have a cardboard and foil heatshield over that right side from the factory. I suspect the M13 FSR board has a much lower power requirement.

The other thing to note is the connectors to the pointing module is different, which is of course expected. The FSR connector is a wider 5 trace connector, while the Trackpoint is a thinner 6 trace connector. The simpler circuitry of the FSR board likely means the Lexmark IC on this board is probably handling more internally than the other IC or the signal processing for the FSR module is simpler. There is a Panasonic IC on the Trackpoint that seems to front the main Trackpoint IC.

Finally I see some very interesting things on the FSR controller, if you look at the areas circled in pink. On the left seems to be an unpopulated 6 pin connector, and since it looks like it is also connected to some of the traces of the current connector I wonder if it is actually a PS/2 output connection for both the keyboard and the mouse since a keyboard out would only need a 4 pin connector. Also there is one connector on the right that is another 5 pin connector exactly like the P/S passthrough on a M13 Trackpoint that connects to the PS/2 mouse passthrough on those boards. I will have to investigate these connectors as if they work I could likely make this board a full PS/2 just like the Trackpoint and even add the passthrough.

I dont know if anyone else cares but I found this comparison very interesting so I thought I would post. It seems info from Admiral Shark that the Lexmark branded M13s with FSR pointers actually came out first in 1993 before any IBM M13s, but were only used for the Lexmark Classic Touch M13 and the Lexmark Erase-Eaze. Once those 2 models ceased production all Lexmark and MaxiSwitch built M13 were Trackpoints, until Unicomp started producing their own FSR pointers keyboards in the late 1990 and by then I think they switched to the pressed connection boards. So likely this controller board is the only FSR that was NOT attached via the PS/2 to a daughterboard and only used in the Classic Touch and Erase-Eaze. I think all other Unicomp on a Stick used separate pointing control boards.

Anyway I will try out those odd extra connectors on this board and see if it actually supports PS/2 but the function was never used since the Trackpoints took over.