Load screen

        Entry:
          AX = CD09h
          CX:BX -> structure (see below)
        Return:
          AL = 00h successful
             = 80h unsuccessful

        Format of structure:

        Offset  Size    Description
         00h    BYTE    style
                        44h ('D') diamond style
                        4Ch ('L') line style
         01h    BYTE    reserved (00h)
         02h    WORD    frequency in lines per inch [sic]
                        currently, coerced to nearest of 50, 60, 68, 70, 75,
                        85, or 100
         04h    WORD    screen angle in degrees (-360 to 360)
                        currently coerced to nearest of -45, 0, 45, or 90