PICkit 2 Connection Questions

Discussion in 'Embedded Systems and Microcontrollers' started by tracecom, Jun 18, 2013.

  1. tracecom

    Thread Starter AAC Fanatic!

    Apr 16, 2010
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    Below is a clip from the Microchip PICkit 2 User's Guide.

    [​IMG]

    In the third bullet point, I take this to mean that the PICkit 2 should be connected to a powered USB port at any time that the PICkit 2 is connected to a target board that has its own power supply.

    Is my understanding correct? And if so, what would be the result if the PICkit 2 was not connected to a powered USB port, but was connected to a target board that has its own power supply?
     
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  2. t06afre

    AAC Fanatic!

    May 11, 2009
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    As I read it, you are corect. My guess is that it can cause some unwanted loading of the target board.
     
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  3. Markd77

    Senior Member

    Sep 7, 2009
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    Maybe it makes the PICKIT work unreliably when it is plugged into USB. If there's just a resistor between the PIC in the programmer and the (powered) target PIC then the PICKIT PIC can be running. Current flows through the protection diodes so it can be powered even if VDD isn't connected.
    I doubt if it would ever cause any damage, but best not to find out.
     
  4. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    You are correct tracecom. Do not connect the PK2 to a power source (on the board end) if you don't have it plugged in via usb. My guess is that if you have, say, 9v on the board side and 0v on the USB side, it could cause some internal components to become reverse-biased when they should not be, and possibly cause damage. Poor design in that sense. I wonder if they fixed it for the PK3.
     
  5. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Simon sez don't do that.

    It's always best to follow his advice.
     
  6. tracecom

    Thread Starter AAC Fanatic!

    Apr 16, 2010
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    You are right, but I wish manual writers would accompany warnings with explanations.

    "Don't do that!"

    Why? Will my PICkit 2 or my circuit explode, smoke, or what? :)
     
  7. t06afre

    AAC Fanatic!

    May 11, 2009
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    If you do this it is chance for that something may happen. What will happen will depend on very much on your circuit. Can not say more. If you find out you have done this error. Do not fix it by plugging in the USB cable. But disconnect the PICKIT from the board, then plug in the USB cable
     
  8. tracecom

    Thread Starter AAC Fanatic!

    Apr 16, 2010
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    Thanks. I had used the PICkit 2 a lot before I read this warning, so it's possible I did what I was not supposed to do. I don't specifically remember doing it, but it's possible.

    But my PICkit 2 still works fine and I am not aware of any damage to my circuits, so, I suppose there's no problem.
     
  9. Brownout

    Well-Known Member

    Jan 10, 2012
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    Since the PICKIT2 is powered via USB, when you first plug it in, the state of the device is unknown, until it intializes. If you have it connected to a powered circuit, unknown things can happen when you plug in the USB cable. You might get away wiht it 100 times, then watch it go up in smoke on the 101st try.
     
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