A method and apparatus are provided for customizing and monitoring multiple interfaces, such as, multiple IEEE 1149.1 standard joint test access group (JTAG) interfaces and implementing enhanced fault tolerance and isolation features. A first interface is connected to a pair of master sources. A second interface is connected to a plurality of target interfaces; and a third interface is provided for a plurality of predefined control signals. A pair of redundant selectors is provided for coupling a select signal to the first multiplexer for selecting one of the plurality of target interfaces. A pair of redundant ATTENTION monitor functions is provided for monitoring ATTENTION signals for each of the plurality of target interfaces.