Apparatus and method of authenticating joint test action group (jtag)

An apparatus that performs joint test action group (JTAG) authentication, the apparatus comprising a JTAG access circuit that determines whether to access a JTAG-compliant device according to a predetermined protocol that governs the JTAG-compliant device and the apparatus, wherein:

• the JTAG access circuit at least one of inactivates at least one of inner bus lines and inner units and activates the at least one of the inner bus lines and the inner units according to whether the JTAG-compliant device is accessed, wherein the JTAG access circuit detects whether the JTAG-compliant device is connected to the apparatus, wherein when the JTAG access circuit detects that the JTAG-compliant device is connected to the apparatus, the JTAG access circuit inactivates the inner bus lines and the inner units, and determines whether JTAG recognition data applied from the JTAG-compliant device is consistent with comparison reference data, and wherein when the JTAG recognition data applied from the JTAG-compliant device is consistent with the comparison reference data, the JTAG access circuit activates at least one of the inactivated inner bus lines and the inactivated inner units.