Abstract: Large number of on-chip instruments support post-silicon validation, volume test, debug, diagnosis and in-field monitoring of an integrated circuit. The IEEE 1687-2014 (Internal JTAG or IJTAG) standard is an effective method for accessing the on-chip instruments. Streamlined access to on-chip instruments through IJTAG is prone to abuse and lead to security issues. An adversary can leak confidential data or get an access to design details of IC through IJTAG network. Recently, locking and unlocking mechanism for IJTAG is proposed to secure the access to on-chip instruments. This paper presents a novel Physical Unclonable Function (PUF) based secure access method for on-chip instruments which enhances the security of IJTAG network and reduces the routing congestion in an integrated circuit.