7.13.2. JTAG Secure Mode
When you enable the tamper-protection bit, Cyclone® V devices are in the JTAG secure mode after power-up. During this mode, many JTAG instructions are disabled. Cyclone® V devices only allow mandatory JTAG 1149.1 instructions to be exercised. These JTAG instructions are SAMPLE/PRELOAD , BYPASS, EXTEST, and optional instructions such as IDCODE and SHIFT_EDERROR_REG .
To enable the access of other JTAG instructions such as USERCODE, HIGHZ, CLAMP, PULSE_nCONFIG , and CONFIG_IO , you must issue the UNLOCK instruction to deactivate the JTAG secure mode. You can issue the LOCK instruction to put the device back into JTAG secure mode. You can only issue both the LOCK and UNLOCK JTAG instructions during user mode.
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