Use input n=1 or input n=2 to feed the port. It is often easier to use than the ALT flag, and sometimes necessary. If channels on both sides of the card are being used, using this flag on both the even and odd channels gives the card the necessay information to keep the port active for the alternate channels when the same side channels are stopped and started. This option requires the MUXCLK=s flag on series-4 cards.