Patent ID: 8516318

Claim:
A test data access system operable on an electronic circuit that includes a plurality of instruments, comprising: a. a test access port including a test data in (TDI) pin, a test data out (TDO) pin, a decode pin, a reset pin and a clock pin; b. a shift register coupled the TDI pin; c. a first multiplexer, in data communication with the TDI pin, configured to receive data from the TDI pin and configured to transmit data to each of the instruments, the first multiplexer also configured to receive data from a data recirculation bit, the first multiplexer further configured to transmit data from the TDI pin to a plurality of instruments when the recirculation bit has a first value and to transmit data to the plurality of instruments from a recirculation line when the recirculation bit has a second value, different from the first value; d. a second multiplexer, configured to receive data from each of the plurality of instruments and configured to transmit data from a selected one of the plurality of instruments, selected based on a value of data in the shift register; e. a first AND gate configured to generate a gates clock to the shift register; f. a second AND gate, responsive to the first AND gate, configured to lock the shift register; and g. a third AND gate, responsive to the first AND gate, configured to control clocking to the plurality of instruments.