I have a production design (that I inherited from another company) with a MKL15Z128 processor. During production programming (with a PE Micro Cyclone), we had a bunch of them fail. There was no serial comm with the chip, and Production was unable to reprogram the parts. I looked at them with a PE Micro Multilink Universal using the KDS software. When I try to program them, I get the message "Device is secure. Erase to unsecure?", and after a couple of attempts the programming fails. Looking at the Reset line on the interface, I see it toggling at about 8-15uS, although it holds low when the interface is trying to do something. There is activity on the other two programming lines.
I'm guessing here - if I assume that the programmer had a bad cable and/or the download got corrupted, is this maybe a watchdog toggling the Reset line? Is it possible that a corrupted download could also lock out device erase? Is this a common occurrence? Is there any way to revive the parts, or do I have to just change them out? The design currently has direct connections to the SWD pins. Is there a requirement (or recommendation) for protection components? Or is the hardware connection to the Multilink generally pretty robust?
I've also seen KDS lose communications with the Multilink, even though Windows could see it in the Device Manager. After rebooting my PC, it worked again. Is this a known problem?