PIC doesn't start witout scope

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  1. - 25th April 2010, 05:18 #1
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    Schematic?
  2. - 25th April 2010, 05:27 #2
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    Here you go
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  3. - 25th April 2010, 05:55 #3
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    What happens if you turn the MCLR diode around?
    Dave
    Always wear safety glasses while programming.
  4. - 25th April 2010, 21:07 #4
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    Quote Originally Posted by mackrackit View Post
    What happens if you turn the MCLR diode around?
    Good call Dave. Is MCLR even a needed function ? Perhaps turn it off in the configs. . . just thinking out loud, if you are controlling motors, maybe an E-STOP and full reset would be safer ?
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  5. - 25th April 2010, 21:16 #5
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    MCLR OFF is not an option for that part. Would be nice if it was...

    Agreed about the full reset. Could save some problems down the road.
    Dave
    Always wear safety glasses while programming.
  6. - 25th April 2010, 22:56 #6
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    Quote Originally Posted by Joe S. View Post
    Good call Dave. Is MCLR even a needed function ? Perhaps turn it off in the configs. . . just thinking out loud, if you are controlling motors, maybe an E-STOP and full reset would be safer ?

    Good catch. Yes, Tobias definetely needs to turn that diode around or it won't work. He can even damage other components in his circuit with the ~12V going to Vpp from the programmer.

    I have a design with a 16F727 where I use a diode and a 4.7k resistor connected to MCRL. Now, reading Joe_S post I just realized that I don't really need this two extra components in my design. In the 16F727 you can configure pin 1 as MCRL or as RE3.

    Robert
  7. - 26th April 2010, 15:33 #7
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    Default schematic screwup

    Guys I appreciate the input and I realize that I have the diode drawn backwards in the schematic compared to the board. The PIC doesn't even program if the diode is backwards.

    The question I have is what happens when I touch the MCLR line with the scope? When I do that, the PIC starts up. Thats the weird deal. I am back at my office now and am going to swap out diodes. Maybe there is just a problem with the diode.

    I will let you know what I find.

    Thanks again
  8. - 26th April 2010, 16:14 #8
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    Quote Originally Posted by Tobias View Post
    Guys I appreciate the input and I realize that I have the diode drawn backwards in the schematic compared to the board. The PIC doesn't even program if the diode is backwards.

    The question I have is what happens when I touch the MCLR line with the scope? When I do that, the PIC starts up. Thats the weird deal. I am back at my office now and am going to swap out diodes. Maybe there is just a problem with the diode.

    I will let you know what I find.

    Thanks again
    Yes, that's weird. Sometimes I forget to remove the programmer from my circuit and when the programmer is off and connected to the circuit my PIC won't work. So, in order to make my PIC work I need to either turn the programmer on or disconnect it from the circuit.

    In your case, what voltage are you feeding MCRL with? Are you sure you are getting this voltage at MCRL? Try replacing the 4.7k resistor also. Try connecting an inductor in series with the 4.7k resistor or a 0.1uF capacitor from MCRL to ground close to the MCRL pin to eliminate posible noise.

    Robert
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