Abstract: A digital system that includes a plurality of integrated circuits disposed on a circuit board, each integrated circuit comprising a plurality of scan chains, each scan chain scanning data from a scan input to a scan output in response to a scan clock; each scan input is coupled to a first pad of the integrated circuit, and the scan outputs are multiplexed to a second pad of the integrated circuit; the second pads of the integrated circuits are multiplexed to a port of the circuit board. A controller selects one of the integrated circuits for scanning, the controller selecting the second pad of the selected integrated circuit for coupling to the port of the circuit board; and the controller also selects one of the plurality of scan chains in the selected integrated circuit for scanning, the controller coupling the scan clock to the selected scan chain and selecting the scan output of the selected scan chain for coupling to the second pad of the selected integrated circuit.