Abstract: A circuit couples a test access port (TAP) having a JTAG interface to another port having a serial interface different from the JTAG interface. The circuit includes a forwarding circuit and a timing control circuit. The forward circuit is coupled to couple a test data in (TDI) terminal, a test data out (TDO) terminal, and a test clock (TCK) terminal of the TAP to an input terminal, an output terminal, and a clock terminal of the another port, respectively. The timing control circuit is coupled to drive a select terminal of the another port with a select signal that activates serial data transfer through the serial interface to a device. The timing control circuit delays assertion of the select signal by a configurable time period after assertion of a shift data state of a state machine of the TAP.