Apparatus selects a state machine bit group from a plurality of state machine bit groups of a digital system for debugging the state machine connected to the selected bit group. The apparatus is adapted to output the bits of the selected bit group using existing output pins of the digital system, and includes a first multiplexer which is adapted to be connected to the plurality of state machine bit groups for outputting the selected state machine bit group. A second multiplexer is adapted to be connected to system signals and the selected state machine bit group from the first multiplexer, and outputs one of the system signals and the selected state machine bit group via the output pins of the system. A control circuit supplies a first select signal to the first multiplexer for selecting the selected state machine bit group output by the first multiplexer, and supplies a second select signal to the second multiplexer for selecting one of the selected bit group and the system signals.