MSP430F6779A: Are there any other condition can cause MCU lock-up and Reset pin High

What do you mean the MCU lock-up. What you do and cause the MCU lock-up?

The PMM26 lock-up means the code will not run. You can set a GPIO toggle after reset. If you find this GPIO not toggle after you reset, that means you meet the PMM26

I cannot re-produce the problem, only check MCU pin, and just want to know how to identify that MCU under lock up or not?

Any other idea to check from existing MCU without flash new code (if re-flash the problem will disappear)?

Can I use Debugger/JTAG attach to a running application to check PC/register without reset the MCU?, I use CCS.

You can try to use SWD to connect MCU. The you will know whether the code is run.

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