US Patent 7734974 Serial scan chain control within an integrated circuit

An integrated circuit 2 includes a plurality of circuit blocks 38, 40, 44 each having an associated serial scan chain loop 32, 34, 36 which extends from a converter 10, to the circuit block 38, 42, 44 in question and then back to the converter 10. Multiplexing circuitry 50, 52 associated with each serial scan chain loop 32, 34, 36 is used to either include that serial scan chain loop 32, 34, 36 in a combined serial scan chain or to bypass that serial scan chain loop 32, 34, 36. The circuit blocks 38, 42, 44 may be bypassed in this way if they are defective or if they are powered-down.