It is next to impossible to help you debug your code with respect to the use of the address 0xFF9E as I have no direct reference or experience with your platform. But if we assume for now that the code you show for setting and clearing a bit at that address is working then you need to be aware of something.

As written your code will put out a very short high level on that pin relative to the long low level time as determined by the delay loop. If you have an oscilloscope you would be able to see the narrow high pulse if you triggered on it and zoomed in the scan speed to capture it. On a zoomed out scope capture rate you may very well miss the narrow pulse.

On the other hand if you were expecting to see something more like a 50% duty cycle square wave on the pin then you would need to put two delay loops in the program; one after you set the bit and another after you clear the bit.

Michael Karas