Test if keystrokes are not waiting.

If a keystroke is waiting, the Carry Flag will be set.

If no keystroke is waiting, the Carry flag will be clear. Also when a parameter is provided, it will jump to that location.

Examples:

    KeyNotPressed              ; test for keystroke
    KeyNotPressed  CHECK_AGAIN ; if a no key waiting continue checking

See also: KeyPressed, KeyWait and KeyRead.