Why does Fn key on laptop does not work when used with an external keyboard?

Question

On my Dell Latitude E6400, the up and down arrow keys are used to change the brightness of the screen when used with the Fn key.

I connected an external keyboard via USB and tried to increase the brightness while pressing the Fn key from the laptop keyboard and the up arrow from the external keyboard.

It did not work. Shift, Ctrl and Alt work correctly when when used this way with an external keyboard.

Why not Fn?

Answer 1

Fn key combinations usually cause the keyboard interface to emit different signals. Since the Fn key is not interpreted by the OS, there is likely no easy way to use it with keys on a different keyboard and have the same result since the keyboard interface isn't listening to the other keyboard.

Answer 2

I'd say because Shift, Ctrl and Alt action the same across all computers. These are standard keys.

Fn functions are specific to the laptop - some need certain drivers on the laptop for them to function correctly, therefore the laptop probably listens for the Fn function and the laptop arrow keys to perform an action, as opposed to an external keyboard which is just treated as your normal 'up and down' keys, regardless of the Fn key.

Answer 3

I think (haven't tried it myself) that the external keyboard does not contain the programming that the laptop keyboard does. I'm guessing that if you have access to the FN key on the laptop keyboard, you also have access to the up/down keys on the laptop keyboard, just use those if it works with the external keyboard plugged in.