We have exactly the same problem. If you have a solution, please send it this way....

The open-video command shows that mode 3 is available, but it is not actually supported. At the time of the last LH75401 LogicLoader release, we were still showing modes that were not actually supported. My guess is that if you try this mode, it will tell you it doesn't work.

What you will have to do is open one of the other modes, that matches your screen parameters and then manually write to the 75401's LCD registers using the 'x' command. I would suggest first writing to the control register to disable the LCD controller, change your timing registers, and then enable the LCD controller.

The naming of the LCD signals are named for a TFT display. Check out the app note for the SDK about interfaceing a LCD. This gives some hints on naming conventions of the signals.
"AN 161 Interfacing LCD’s to Logic’s SDK Board"

In order to determine the correct Data signals to hook up to your STN display, you can track the LCD data lines back to the processor on the schematic. Logic names them colors, but you can see where they map to on the processor. Then use the LH75401 User Guide from Sharp to determine the correct data signals that need to be used to hook up to the STN.

Thanks,
Mike A.