INT 60 u - HP 95LX System Manager - LET SYSTEM MANAGER HANDLE MENU KEYSTROKE
        DI = 0204h
        STACK:  2 WORDs unused dummies (for calls from high level languages)
                DWORD   pointer to menu data (see INT 60/DI=0200h)
                WORD    keystroke
                DWORD   pointer to WORD to receive selection number
Return: buffer for selection number filled with index of selected menu item or
          FFFFh if no final selection yet
        STACK unchanged
SeeAlso: INT 60/DI=0200h,INT 60/DI=0202h,INT 60/DI=0207h