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Electronics Engineering QUESTION #11748
Question 1
In JTAG boundary scan testing of a PCB, the instruction register is loaded with EXTEST. This allows:
  • Reading the internal device ID code
  • Bypassing all logic to create a single shift register through all devices
  • Forcing logic values at device I/O pins to test board interconnects✔️
  • Enabling the internal self-test of each IC
Correct Answer Explanation
EXTEST (External Test) is a JTAG boundary scan instruction that places all boundary scan cells in external test mode — allowing the test controller to force and observe logic levels at every pin of each device on the board. This enables testing of PCB interconnections (open/short faults, stuck-at faults) without physical access to individual pins, non-invasively.