If you are running 2.7 this button now defaults to Macro 821.
However, you can change this mapping to any other macro, or any hard key in the "Buttons" tab, within the "Settings" section of the Shell. You'll have to scroll down to the bottom, it's labeled "Programming Wing/Ion XE/Element 2 Buttons".
Just to be clear, you can still re-map the key in the shell in previous versions, it just defaulted to Macro 20, where other devices defaulted this key to Macro 821. With 2.7 they made everything 821 for consistency. If you haven't updated yet (and you're not in the middle of a run) I would highly recommend making the jump, many many great changes and new features; though it might take a bit to get used to the new tombstone shape!