10.1.3. JTAG Secure Mode
If you enable the tamper-protection bit, the Stratix® V device is in JTAG secure mode after power up. In the JTAG secure mode, the JTAG pins support only the BYPASS, SAMPLE/PRELOAD , EXTEST, IDCODE, SHIFT_EDERROR_REG , and UNLOCK instructions. Issue the UNLOCK JTAG instruction to enable support for other JTAG instructions.