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strange problem

Discussion in 'Microcontrollers, Programming and IoT' started by jimtr6, Jul 2, 2010.

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  1. jimtr6


    Jun 16, 2010
    I programmed a 12F629 and inserted it into my breadboard and it works fine, so I put it on my perfboard in a socket and it will not work, it has an internal oscillator so my connections are only voltage supply and ground, no other connections to the ports, the program simply turns a port on high when I apply a high to to an input. I took it out put it in the breadboard again and it works, I'm just using a logic probe at this point although on the breadboard it lights the LED if I hook it up. I'm baffled, I even made a second board thinking there was a strange issue with the first, still no go, I'm using two boards, one is perfboard the other is Radio Shacks Archer experimenter board made for TTL, neither one will work. No shorted or open pins, voltage and ground are on the pins of the chip, what could cause this??? much appreciated if I can get any help with this.
  2. davenn

    davenn Moderator

    Sep 5, 2009
    it really most likely is a mistake in the more permanently wired board you have done
    PIC chips are not that touchy to make work ...something has been overlooked ;)
    I couldnt imagine anything else

  3. jimtr6


    Jun 16, 2010
    I checked and double checked, actually built second third and fourth boards,those just having voltage supply and ground, no input or output connections to pins, just using a logic probe. The boards with no input will allow the chip to operate (just LED flash), the programs looking for a high on GPI05 and then making the LED flash is a different story, I have added pull down resistors which I should have done from the beginning but the Experimenter Board from Radio Shack just will not work, this is strange stuff, as I said there are no connection issues, I checked double checked, it is something that evades me, oh ya, did 47uA cap across the rails and high frequency caps on inputs....puzzled
  4. PopleWebDesign


    Jul 9, 2010
    Presumably you got this sorted, but one of the key things I keep finding with Micros is the need for a decoupling (noise reducing) capacitor across the chip's supply as close as possible to the chip, I usually pop a ceramic 104 on the bottom of any veroboard on any microcontroller that is in use. Works a treat with the PIC16F84A s that I usually use same for GAL.

    Literally across the bottom of the chip holder. (not ideal when it comes to not damaging the circuit but quick easy and reliable for a prototype).

    Best of luck.

  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    The other issue is that there may be a reset pin left floating. The programmer may be holding this pin to an appropriate level, but if left floating it may cause the uC to be reset continually or intermittently.

    The fact that the reset pin can be programmed to act in different ways means that you can do this accidentally.
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