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Keep damaging Freescale 9S12X micro BKGD port
Tom H. Jun 18, 2015 at 12:10 PM (12:10 hours)
Staff: Johnny N.

  • Over the last couple weeks we have damaged the BDM port on three Freescale micros. The pin seems to be shorted to 5v. This happens during connection of the USB ML-12E programmer. We have used these programmers for years along with the same processor and have not seen this problem before. Processor runs, but we can no longer program it. The reset line is pulled up to 5v with a 4.7k resistor and the BKGD pin is pulled up to 5v with a 3.3k resistor.

    Previous processor damage occurred when plugging the USB ML-12E onto the target when the target was powered up. The last unit was damaged when plugging the programmer to the target with the target powered off.



    • Tom,

      We have the following guidelines to avoid electrical damage to any P&E interface.

      1. We recommend using regulated power supplies, have the board be free of shorts, and avoid transients/over-voltage on communication/power lines.

      2. We recommend against plugging the interface into a hot target. This means that you should always turn off the target power before connecting/disconnecting the ribbon cable to the target board.

      3. We recommend users utilize anti-static protection devices.

      If you can determine which BDM pin is shorted/damaged, I can try to assist you in the repair of your faulty multilinks. One test you can do is to check resistance on the BKGD, RST, and VDD pins with respect to gnd using a multimeter.


    • Hi Tom,

      It has been a couple of months so I just wanted to follow up with you to see if you were still running into the same issues.

      P&E Engineering Support

  • Hi Johnny, 

    Thanks for the reply.

    The programming module is fine, the damage occurs on the freescale processor pin 23 MODC/BKGD. It is shorted to 5v. There must be an internal protection diode that gets shorted. Once we replace the processor all is well again.

    We will follow your recommended guidelines and see if it happens again.


    • Hi Tom,

      What is the MCU? Is it always the BKGD pin that is damaged? What software are you using to program the part?


  • Johnny, 

    It is a Freescale MC9S12XEP100MAL. It is always pin 23, MODC/BKGD (112 pin part). We are using Codewarrior.

    We have been using this MCU / programming module setup for years. Recently we have been experiencing this shorted to vcc pin issue. Same setup, same people using it, same processes. The people doing the programming (including myself) are experienced engineers that have developed may products with this MCU / programmer combination.

    One thing that we have been doing (again for years, right or wrong, without issue) was hot plugging the programmer to the target pcb. After the second time a processor was damaged we started connecting the programmer with the target powered down. Working with the same board under development, we experienced the same problem yesterday. Went to program the device (connected programmer with target powered down), get a "can't communicate" error, check the BKGD pin - shorted to vcc, replaced processor and all is working again.

    We have a couple programming modules here and are considering swapping this one out to see if it happens with a different ML-12E.


    • Tom,

      If it is always pin 23, then you are exceeding the maximum ratings for that pin. According to the table A-1 in the reference manual, the absolute maximum current is 25 ma and maximum voltage is 6V.

      Do you have any other components that are connected to the BKGD line?

      Which version of Codewarrior are you using?


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