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Hot!Sneaky pin change in pic32mx274

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nigelwright7557
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2019/09/18 10:34:00 (permalink)
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Sneaky pin change in pic32mx274

I designed a USB oscillscope using the PIC32mx220.
Everything worked out ok.
I then decided to do a dual channel scope.
So I looked up faster pic32mx with more memory.
I picked the pic32mx274 which has same pin out, great stuff.
Got my new pcb built up and the scope voltages range wasn't being selected properly.
Turns out RA4 is now an input only pin.
This is despite Harmony showing it can be an output or numerous other modes.
So I needed a cut and a link to get the pcb working.
 
#1

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    ric
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    Re: Sneaky pin change in pic32mx274 2019/09/18 13:26:16 (permalink)
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    I would guess that was an unintended side effect of the low power secondary oscillator on that pin.
    Rev A of the datasheet says nothing about it being input only, and there is a TRISA4 bit.
    Rev D of the datasheet has an extra footnote on the pin assignment tables, saying:

    Except for default primary function on this pin, all alternate functions can be input only. Do not attempt to use or assign an output feature.

    The "primary" function is "SOSC".
    TRISA4 still exists, but plainly is non-functional.
     

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    #2
    ric
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    Re: Sneaky pin change in pic32mx274 2019/09/18 13:28:33 (permalink)
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    Wow. 52 items in the errata list, and this is NOT one of them.
     

    I also post at: PicForum
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    #3
    LostInSpace
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    Re: Sneaky pin change in pic32mx274 2019/09/24 10:44:25 (permalink)
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    Microchip apparently does not consider pins not working as a 'worthy' errata.
     
    The PIC32MZ RF3 pin not working as an output if VUSB is not tied to +3.3V is not mentioned anywhere.
     
    I wonder how many PCB's have a jumper on them to 'work around' this issue? I know one of mine does!  ;-)
    #4
    simong123
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    Re: Sneaky pin change in pic32mx274 2019/09/24 12:12:57 (permalink)
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    SteveHageman
    The PIC32MZ RF3 pin not working as an output if VUSB is not tied to +3.3V is not mentioned anywhere.

    Yes it is. See e.g. table 1-14 in the MZ..EF datasheet (although it could be worded better, and be more prominent).
    #5
    LostInSpace
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    Re: Sneaky pin change in pic32mx274 2019/09/24 16:31:14 (permalink)
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    You are right! That is VERY obtuse wording however, some might even say Diabolical. Naturally USBID would not be available if not using the USB function, but that seems a long way from saying that RF3 won't work. You have to make the mental jump to: "Shared pin". Heck, most days I have trouble making the Mental Jump to: Waking up !!!!!  ;-)
     
    #6
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