1. A method of coupling a plurality of test access port (TAP) controllers to a single external interface, comprising: resetting a first bit in each of plurality of TAP controllers ( 102 , 106 ) to a known state; producing a first signal based, at least in part, on the state of the first bit in each of the plurality of TAP controllers ( 102 , 106 ); selecting one ( 108 ) of the plurality of TAP controllers based, at least in part, on the first signal; coupling an external input terminal to an input terminal of the selected one of the plurality of TAP controllers; and coupling an output terminal of the selected one of the plurality of TAP controllers to an external output terminal.