Microprocessor apparatus and method for securing a programmable fuse array

An apparatus in an integrated circuit for precluding the use of extended JTAG operations, the apparatus comprising:

• a microprocessor, comprising:
• a JTAG control chain, configured to enable/disable the extended JTAG operations;
• a feature fuse, configured to indicate whether the extended JTAG operations are to be disabled;
• a level sensor, configured to monitor an external voltage signal, and configured to indicate that said external voltage signal is at a legal level;
• an access controller, coupled to said feature fuse, said level sensor, and said JTAG control chain, configured to determine if said feature fuse is blown, and configured to direct said JTAG control chain to disable the extended JTAG operations if said feature fuse is blown, and configured to direct said JTAG control chain to disable the extended JTAG operations if said external voltage signal is at an illegal level regardless of whether said feature fuse is blown;
• and
• a blow controller, coupled to a fuse array, configured to receive a voltage, and configured to blow a selected fuse within said fuse array responsive to a value of said voltage, wherein blowing of said selected fuse is allowed only when the extended JTAG operations are enabled.

A method for precluding the use of extended JTAG operations in an integrated circuit, the method comprising:

• via blowing a feature fuse that is disposed within the integrated circuit, indicating that extended JTAG operations are to be disabled;
• first determining if the feature fuse is blown, and directing a JTAG control chain to disable the extended JTAG operations;
• second determining if an external voltage signal is at a legal level;
• disabling the extended JTAG operations if the feature fuse is blown, and directing the JTAG control chain to disable the extended JTAG operations if the external voltage is at an illegal level regardless of whether the feature fuse is blown;
• and
• receiving a voltage, and blowing a selected fuse within a fuse array responsive to a value of the voltage, wherein said blowing is allowed only when the extended JTAG operations are enabled.