pic18F6722 issues


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  1. #1
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    Default pic18F6722 issues

    Hi all,
    I'm trying to bring up a pic design that's using an 18F6722. I've used these parts about 8 times in the past but this one is really stumping me. As far as I can tell, this design is not much different from any of the others. It is an XBEE transceiver for my solar panel system to monitor the current and voltage delivered by my solar panels. This board serially connects to my V-I monitoring board that measures the PV array current and voltage.
    When I try to program the PIC, I get "Target Device does not match selected device" error. I see on my scope that the oscillator is not functioning. I'm not sure if that's what is stopping the programming sequence. When I use my MELABS USB programmer to read the device, the Config bytes appear to be set but all code space is "FF" on a part that I just soldered onto the board.
    I have all the programmer connections exactly the same as my last functioning design and have the digital PGM pin 43 pulled low on the 64 pin part. I'm using the same 18pf caps on the crystal to ground as I've use MANY time before.
    The MCLR pullup is 4.7k Ohms as I've used in the past too.
    I'm really stumped on this one...

    Has anyone more things check?

    Thanks,
    Brian
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  2. #2
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    Default Re: pic18F6722 issues

    a .pcb file is never that handy if you don't have the right software Can you export it to PDF any image format? Case not, install PrimoPdf. Ask your software to print but select PrimoPDF as your printer... easy easy
    Steve

    It's not a bug, it's a random feature.
    There's no problem, only learning opportunities.

  3. #3
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    Default Re: pic18F6722 issues

    This error message may be due because your PGD/PGC/MCLR line are loaded... or sometime because the PGM pin is not loaded to gnd. Or worst... you haven't selected the right device in your device programmer software... oh yeah it happen even if you already did it millions time before
    Steve

    It's not a bug, it's a random feature.
    There's no problem, only learning opportunities.

  4. #4
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    Default Re: pic18F6722 issues

    Hi,
    I've add the PDF generated by primoPDF.
    I have the PGM pin pulled low by a 4.7k. I will scope the PGD abd PGC lines next. There is nothing different about them from my other working designs but then there is always something else possible. I have only the parts populated that have to do with programming the PIC. The eepoms are not on the board yet nor is the XBEE transceiver.

    Thanks,
    Brian
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  5. #5
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    Default Re: pic18F6722 issues

    Schematic please..........
    Steve

    It's not a bug, it's a random feature.
    There's no problem, only learning opportunities.

  6. #6
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    Default Re: pic18F6722 issues

    Hi,
    ExpressPCB has a schematic capture but I don't usually spend the time with it. I "read" the PCB instead.

    Brian

  7. #7
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    Default Re: pic18F6722 issues

    Hi,
    Here is the basic schematic as I pulled it off of the .PCB file view.
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  8. #8
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    Default Re: pic18F6722 issues

    Hi,
    I scoped the DAT and CLK lines and they see that the data line is not transitioning to ground very far (about 1/3 the way).
    I measured the resistance of CLK and DAT to ground and VCC and they are open.
    I don't see in the artwork any overly close traces suspecting an under etched via causing a short but don't see anything.

    Brian

  9. #9
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    Default Re: pic18F6722 issues

    Darned bypass caps... didn't have enough of them. Newest Artwork Programs fine.

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