Serial scanning circuitry is connectable to test access port controller for transferring serial data to and from functional circuitry. The test access port controller includes a first state machine having plural states controlling the transfer of serial data. Additional control circuitry includes a second state machine connected to the serial scanning circuitry and connected to the test access port controller. The additional control circuitry, when connected to the test access port controller, effects the providing and receiving of signals between the serial scanning circuitry and the functional circuitry and the transferring of serial data to and from the serial scanning circuitry continuously without interruption while the first state machine remains in one state.