A USB port transmitter includes a plurality of arbiters, each employing a distinct priority rule to select one USB transmission from among multiple scheduled USB transmissions based on their types. A selector selects one of the arbiters to select the one USB transmission from among the multiple scheduled USB transmissions. A programmable storage element controls the selector to select the one arbiter. In one embodiment, at least a first arbiter prioritizes header/data packets higher than link commands, and at least a second arbiter prioritizes link commands higher than header/data packets. In one embodiment, at least one arbiter prioritizes flow control and power management link commands higher than header/data packets. In one embodiment, at least a first of the arbiters prioritizes USB LGO_Ux link commands higher than USB LAU/LXU link commands, and at least a second arbiter prioritizes USB LAU/LXU link commands higher than USB LGO_Ux link commands.