DEBUG Boundary scan

The RESET pin selects between the JTAG boundary scan (RESET = LOW) and the ARM SWD debug (RESET = HIGH). The ARM SWD debug port is disabled while the part is in reset.

To perform boundary scan testing, follow these steps:

  1. Erase any user code residing in flash.
  2. Power up the part with the RESET pin pulled HIGH externally.
  3. Wait for at least 250 μs.
  4. Pull the RESET pin LOW externally.
  5. Perform boundary scan operations.
  6. Once the boundary scan operations are completed, assert the TRST pin to enable the SWD debug mode and release the RESET pin (pull HIGH).
Note: The JTAG interface cannot be used for debug purposes.
Note: POR, BOD reset, or a LOW on the TRST pin puts the test TAP controller in the Test-Logic Reset state. The first TCK clock while RESET = HIGH places the test TAP in Run-Test Idle mode.

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