Port 3C0, 13  -  Horizontal PEL Panning

          111x xxxx  Reserved
          xxx1 1111  Horizontal PEL Panning

          Bits 4-0:  These bits select the numer of PELs that the video
                     data is shifted to the left. PEL panning is availeble
                     is both alphanumeric and graphics modes. The following
                     figure shows the number of bits shifted for each mode.

                     Register  Mode     A/N      All Other
                     Value     13       Modes.   Modes  
                     0         0        1        0
                     1         -        2        1
                     2         1        3        2
                     3         -        4        3
                     4         2        5        4
                     5         -        6        5
                     6         3        7        6
                     7         -        8        7
                     8         -        0        -

                     .Only mode 7 and the A/N modes with 400 scan
                      lines.