Port 3FB  -  Line control register

        1xxx xxxx  0=normal, 1=address baud rate divisor registers (3F8/3F9)
        x1xx xxxx  0=break disabled, 1=enabled
        xx11 xxxx  00=Odd parity
                   01=Even parity
                   10=Parity bit is always 0
                   11=Parity bit is always 1
        xxxx 1xxx  1=Parity selected, 0=No parity
        xxxx x111  000=5 bits/character, 1 stop bit
                   001=6 bits/character, 1 stop bit
                   010=7 bits/character, 1 stop bit
                   011=8 bits/character, 1 stop bit
                   100=5 bits/character, 1.5 stop bit
                   101=6 bits/character, 2 stop bits
                   110=7 bits/character, 2 stop bits
                   111=8 bits/character, 2 stop bits

        When bit 7=1 port 3F8/3F9 determines communication speed:

                                              Error between
                Baud rate      3F9  3F8    desired and actual
                    50           09  00             -
                    75           06  00             -
                   110           04  17           0.026%
                   150           03  00
                   300           01  80
                   600           00  C0
                  1200           00  60
                  1800           00  40
                  2400           00  30
                  3600           00  20
                  4800           00  18
                  7200           00  10
                  9600           00  0C
                 19200           00  06
                 38400           00  03
                 56000           00  02           2.860%