An enhanced JTAG interface provides an additional clock output at any desired I/O port of a logic device during normal operation. The interface includes a boundary scan data cell associated with each I/O port that enables either input data to the I/O port in a normal mode or routes the boundary scan input data during a JTAG operation. A control cell is associated with each data cell for selectively enabling either a normal mode or a JTAG mode of the boundary scan cell. A set of JTAG instructions enable/disable JTAG operation and select JTAG functions. The boundary scan data cell is modified to incorporate a multiplexing arrangement to selectively route the JTAG clock to the I/O port when required. The control cell is modified to selectively enable/disable the routing of the JTAG clock in the boundary scan data cell.
