ULPWU AND ICSP, conflict ?


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  1. #1
    Join Date
    Nov 2003
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    98

    Default ULPWU AND ICSP, conflict ?

    Hi
    on the PIC16F690 16F684 and other chips the ULPWU pin is shared with the ICSPDAT pin
    how can i program these on board with a fair sized cap there ?
    anybody have an experience with this ?

    seems like a poor choice of pin sharing to me
    i suppose i could put a jumper to switch out the cap but that would have to be set for every flash cycle during development

    or maybe there is some maximum value that would still work with the programmer? I am using the ME U2B

    thanks

  2. #2
    Join Date
    Nov 2003
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    I now have some data that I have taken that answers this question

    for ULPWU caps 0.01uF - 1.0uF the MEL U2 programmer works fine if a resistor is placed in series with the cap value >= 470 Ohms

    without the resistor the programmer will not work for that range of caps

    during the deep sleep the resistor will have little effect since the discharge current is only 200nA so only a small offset error is introduced

    during charge at wake up the resistor will slow the charging of the cap but this shouldn't be a problem for most apps, either arrange a short delay or see if the time to execute the tasks at hand will swamp that charge time anyway

    BTW, i figure that 0.022uF will produce a poll period of about 0.5secs, we will see

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