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MC9S12D64 - COP Reset

Question asked by Lucas Sinopoli on Mar 30, 2017
Latest reply on Apr 5, 2017 by Radek Sestak


I'm having issues with the watchdog (COP) reset in MC9S12D64.
I've read the manual S12CRGV4 and understand the workings of the reset for the MCU.


I've tried/verified the following:
- The vector is properly set. All reset conditions (external pin, COP, and clock monitor) are pointing to the Startup code.
- The circuitry on the reset pin consists of a pull-up, a 1nF cap, and a power supply reset monitor IC (ILC5061). However, I've tried disconnecting the capacitor and changing its value, as well as the IC and the system still can't properly reset.
- I've tried two ways of triggering the reset:
         1. Letting the COP expire without restarting it,
         2. Writing COPCTL = 0x01, and ARMCOP = 0x60. (the manual say that writing anything diferent that COPCTL = 0x01,ARMCOP = 0x60 will cause the reset)


The symptoms I observe are the following:
- When I meassure the reset pin on the oscilloscope, its voltage goes from 5V to near 0V for about 34us, then depending on the value of the capacitor that I have connected to it it'll go back to 5V in a few microseconds.
- When the reset happens the micro gets stuck into some strange state (perhaps a continuos reset?) and doesn't excecute the application at all.
- In some units the the issue is not present, and I've measured the capacitor values in such units, as well as observed the signal at the reset pin, and it looks identical.
- Both of the techniques mentioned above showed the same missbehavior.

Could someone provide me with some help?

Thanks so much!