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Hot!Resistor on MCLR

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Wanglesnap
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2019/12/08 07:38:53 (permalink)
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Resistor on MCLR

It has been recommended to use a 100R ballast resistor on MCLR on some PICS ,any thoughts on this like will it cause damage? , can I use it for all PICS by leaving it in my programming lead?,I am using a 3watt it just gets warm.
Thanks
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    Mysil
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    Re: Resistor on MCLR 2019/12/08 10:00:11 (permalink)
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    Hi,
    100 Ohm sounds wrong, and 3 Watt resistor getting warm is definitely wrong.
    What have you actually hooked together? Schematic!
     
    A 100 Ohm resistor in series in the line between MCLR pin and programming connector may be O.K.
    When the programmer tool is disconnected, it will be open-ended anyway.
     
    The MCLR pin should be pulled up to Vdd power line by a 10 kOhm resistor.
    Some PIC devices have internal weak pull-up that may be used instead of external pull-up resistor.
     
    If there is a Reset switch, and or a Capacitor connected to the switch, some datasheets show such circuits,
    then there should also be a resistor with value between 470 Ohm and 1 kOhm,
    between switch/capacitor connection, and MCLR pin.
    This serve 2 purposes: 
    1: Preventing any bouncing current from switch and capacitor from causing undershoot voltage on MCLR pin.
    2: Signal isolation when Programmer tool drive the MCLR pin for Reset or High voltage programming.
    If there is Reset button, there should still be 10kOhm pull-up resistor from switch to Vdd supply.
     
    These are all my opinions,
        Mysil
    #2
    ric
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    Re: Resistor on MCLR 2019/12/08 12:25:42 (permalink)
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    Wanglesnap
    It has been recommended to use a 100R ballast resistor on MCLR on some PICS

    Where did you see this?
    I am guessing you have been reading about problems some people have had with PK4 and ICD4 when used with old PIC's that require 13V Vpp, and the resistor wired in series with VPP/MCLR is suggested to limit current.
    Context is vital here. It matters what chips you are programming, and what programmer you are using.
     
    As Mysil said, if you have a 3W resistor mounted somewhere, and it is getting warm, then there is something very wrong!

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    Wanglesnap
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    Re: Resistor on MCLR 2019/12/17 09:44:10 (permalink)
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    Sorry late replying, you hit the nail on the head it has been recommended for some old pics but I'm learning on old pics like 12f508,16f628, etc. These chips were getting quite warm and failing during programming but the resistor seems to have stopped this. I am going to recheck after mplabx v5.30 upgrade.
    #4
    Wanglesnap
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    Re: Resistor on MCLR 2019/12/17 09:49:06 (permalink)
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    I should mention I program with pk4 and a zif stand-alone programmer with 20k pull up.
    #5
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