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ICSP Question

Discussion in 'Oshonsoft' started by Roger Harrold, Feb 28, 2015.

  1. Roger Harrold

    Roger Harrold New Member

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    Can anyone tell me what happens to general purpose digital I/O lines during ICSP programming?
    Not the ICSP data/clock lines, but other I/O. Are they low, high, floating?
     
  2. granddad

    granddad Active Member

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    Roger Usually after the ICSP program reset I/O are all input , and presumably during loading , however I have seen some ports show output activity during program, especially the UART pins...

    We are talking PIC here ..?
     
    Last edited: Feb 28, 2015
  3. Ian Rogers

    Ian Rogers Super Moderator Most Helpful Member

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    Most pic pins are in reset when programming and all IO's default to input!
     
  4. dave

    Dave New Member

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  5. Roger Harrold

    Roger Harrold New Member

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    "We are talking PIC here ..? "
    Yes, sorry, should have been more specific. PIC18F1320

    My application has the PWM pins driving an H-Bridge motor driver.
    The motor goes to full speed during programming, and given the replies here I suspect it is because
    the pins are inputs and floating, so the H-Bridge pins are undefined. I'll trying grounding them via
    10k resistors so that go to 0v during programming.

    Thanks for the replies.

    Roger
     
  6. blueroomelectronics

    blueroomelectronics Well-Known Member

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    I/O pins go into input floating mode.
     
  7. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    If the H-bridge used not enable and the outputs were really TTL compatable, float high you would not have that problem.

    The ULN2003 is an interesting device because when the inputs are open, the output is effectively low. Low is low and high is high. So, this solves the problem on start-up where the output is defined as an input.

    There is another CMOS interface chip that does wierd, but predictable things with open CMOS inputs. Something like --- it maintains the previous state when the input tri-states.
     

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