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pic 16F819 will not program

Discussion in '8bit Microcontrollers' started by Niels Damsgaard-Sørensen, Aug 22, 2004.

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  1. Hi group. Before i'm pulling out all my hair (still a bit left), i better
    ask for some advice here:
    I'm working on two different boards, both with a'n Pic 16F819 SOIC. I have
    made a lot of these boards earlier, programming onboard with a Picstart.
    This time i made up 20 of each and started programming the same o'l Hex to
    the boards, but nothing semed to work. Took the whole lot with me home for
    the weekend and tried my own ICD2. Same result :-( Problem seemes to be,
    that all chips are write/code protected. Im sure i made the fusesettings in
    MPLAB right, no fusesettings in software. In Microchips errata it says these
    chips can be difficult, in the Picstart helpfile in MPLAB it says : add a 1k
    pulldown to MCLR. Could failing to do so cause the chips to be
    code-protected ? And should i not be able to remove ALL fuses with a general
    Any ideas ?

  2. Protection on the F parts doesn't stop you from erasing the chips and
    programming them. Could they be in LVP mode? Try a 1K pulldown on PGM.

    BTW, whatever problem it was with the flash does not appear on the
    current errata. I wonder where Microchip squirrels away the older
    errata sheets? I ran into a problem with the 16F628 (buggy CCP module)
    that could have used an errata sheet that matched my samples (only a
    year and a half old).

    Best regards,
    Spehro Pefhany
  3. Thanks for your help Spehro - but:
    Tried that. Did that. No luck.
    Still on verifying it states: Config bit errors .....
    I have erased, resat, etc. a thousand times but with the same bad luck. By
    the way - all my machines are now running XP.
    Last time i did this i think it was 98 on the labtop?
    Just programmed some DIL 16F877 with a simple "blink a LED". Both
    programmers works fine.
    I think i know one customer who's gonna blow a fuse tomorrow.
  4. I got it !!
    In the MPLAP helpfile for Picstart it says that when programming 16F818
    /19's you must use a 1K from MCLR to GND! It must be a pullUP !!
    What really tricked me was all the "helpfull" errormessages in Mplab, saying
    that it erased and that config bits was like this and like that. Only when i
    tried erasing, programming and reading without any pic connectet, and still
    got the same message about "read" config bits and protected memory i
    suspected that the programmer was not talking to the pic at all.
    I guess you guys all knew about this, but to a non-educated fool like me,
    this sort of help is not helpfull at all :-((

    When i get elected king of Sweden, Microchip WONT be in for a Nobelprice for
    this one.

  5. Gary Morton

    Gary Morton Guest

    So do you need a pulldown to gnd or a pullup to vdd?
    I have a board with two PIC16F819s which are both programmed using a header
    for ISP. They both used to program OK, but now one still programs but the
    other does not. I was going to unsolder (surface mount) and replace, but I
    will try your suggestion of pull up/down.

    Thanks for raising this issue

  6. The6502man

    The6502man Guest

    I would assume pull up, since MCLR is an active low reset pin. I
    usually use a 4.5K or so myself.

  7. Al Klein

    Al Klein Guest

    I have a 16F84 that does the same thing. Pull MCLR up and it won't
    erase or program. Pull it down and it does. Since the board has MCLR
    pulled up I had to add a pulldown on the programmer.
  8. I have a 16F84 that does the same thing. Pull MCLR >up and it won't
    Point is, that Microchip specifically say about the 16F818/9 that it is
    special because that it needs a 1K pull_down_.
    AND (in my case anyway) it should be a pull_up_.
    Before i read this, i used nothing and found, that the chips was a bit
    unstable to program, but it worked. (I did actually unsolder a few soic
    Pic's because they did'nt work and i suspected i had fryed them by
    accident.) Then i found their corrections mentioning the pulldown and then
    _nothing_ worked. And again i unsoldered some chips before i (by accident)
    tried the pullup. Offcourse i'm the one to blame because i just did as i was
    told without thinking myself, but you know, i thought Microchip know about
    their own products so i looked everywhere else for the cause of my problems.
    And the various errormessages in Mplab kept me from suspecting the actual
    download-process causing the problems.

  9. Al Klein

    Al Klein Guest

    A pullup allows the uProcessor to start running as soon as the
    programming is complete. A pulldown prevents it from running.
    Neither one should have any effect when the programming pin is made
    active. That's just my opinion.
    Someone's learning from uShaft? (How to write totally meaningless
    error messages?)
  10. Johan

    Johan Guest

    try the following connection for /MCLR

    Vdd- 10k - | - 1n4148-> - /MCRL
    | - 10uF - gnd

    In this the how Microchip suggest in their ISP-guide. Works everytime

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