+19200, 38400, 57600, or 115200. Your hardware may limit your baud
+rate choices.
+.Pp
+For multiport cards the
+.Nm flags
+keyword in the kernel configuration file determines which port of
+your multiport card is the master device, and whether the
+port is part of a multiport card. The master device is the port which
+has register through which all interrupts of the card are funneled.
+All ports of a multiport card report pending interrupts using this
+single register.
+.sp
+The master device is indicated
+.Nm bitwise
+, so all sio entries in the kernel config file that are part of a
+multiport card must include the correct
+.Nm flags
+specification. The bitwise assignment allows multiple multiport cards to
+be configured in one system. It does
+.Nm not
+imply that the hardware can share the same physical interrupt line!
+.Pp
+In the synopsis the
+.Nm flags 0x401
+means that the 4th port (sio4) is the master
+device (so the MSB of the flags), and that the ports are part of a
+multiport card (the LSB of the flags, actually only the LS
+.Nm bit
+).
+F.e. if you have only two standard ports in addition to multiport
+card, this
+.Nm flags
+will be
+.Nm 0x201 .
+.Pp
+Which port is the master device depends on the card type. Consult
+the hardware documentation of your card.
+.Pp
+Serial ports controlled by the
+.Nm sio
+driver can be used for both dialin and dialout. Use
+.Xr comcontrol 8
+to enable/disable bidirectional use of the
+.Nm sio
+ports. The minor number of the dialout
+port is 128 higher than that of the corresponding dialin port. Use
+.Xr stty 1
+to enable or disable modem control as required by your setup.