Ashleigh, I will try to look into this and digest all of the things that you have already done. Your comment about USB9 and the regulators being turned off reminded me that the following errata is in work and may be applicable and wondering if increasing the decoupling capacitance on DVCC/AVCC would help. If the device is powered via the 3.3V USB LDO the BSL invoke might not work once the USB cable is plugged in depending on the on board capacitance connected to DVCC/AVCC. The failure will be caused by the BSL code which is creating a voltage dip on the supply preventing successful code execution. Workaround 1. Increasing the capacitance on DVCC/AVCC (typical 30 uF). However site effect on application needs to be considered. Or ... Regards, Chris
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