PIC16F1503 Fixed Voltage Reference


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  1. #1
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    Default PIC16F1503 Fixed Voltage Reference

    Hi All,

    I am working with a PIC16F1503 and would like to use the Fixed Voltage Reference (FVR) as the reference for the ADC.
    I have successfully done this in the past using a PIC16F1829 but the same register settings do not apply for the PIC16F1503.

    In the case of the '1829:
    From the datasheet, setting ADPREF<1:0> to "11" means "Vref+ is connected to internal Fixed Voltage Reference (FVR) module

    In the case of the '1503:
    From the datasheet, the only two setting options for ADPREF<1:0> are "00" (Vrpos is connected to Vdd) and "10" (Vrpos is connected to external Vref+ pin)
    All other options are "Reserved" and there is not FVR option listed.

    Can anyone enlighten me on how to use the Fixed Voltage Reference (FVR) as the reference for the ADC on a PIC16F1503?

    Cheers
    Barry
    VK2XBP

  2. #2
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    Default Re: PIC16F1503 Fixed Voltage Reference

    a quick look at the data sheet leaves you with only two option for positive reference
    vdd or external vref
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    Warning I'm not a teacher

  3. #3
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    Default Re: PIC16F1503 Fixed Voltage Reference

    Hi Richard,

    Yes, I see that now but contradictory to this diagram, the datasheet also states that the output of the FVR can be configured to supply a reference voltage to the ADC input channel:

    Name:  PIC16F1503 FVR.jpg
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    and this is supported in the FRVCON register (bits 1-0) regarding the relevant ADC FVR buffer gain:

    Name:  PIC16F1503 FVR2.jpg
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    Which one is to be believed?

    Cheers
    Barry
    VK2XBP

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    Default Re: PIC16F1503 Fixed Voltage Reference

    it could be worded better. the hight-lighted word "reference" could be removed to better reflect reality

    The Fixed Voltage Reference (FVR) is a stable voltage
    reference, independent of VDD, with a nominal output
    level (VFVR) of 1.024V. The output of the FVR can be
    configured to supply a reference voltage to the
    following:
    • ADC input channel
    • Comparator positive input
    • Comparator negative input
    The FVR can be enabled by setting the FVREN bit of
    the FVRCON register
    Warning I'm not a teacher

  5. #5
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    Default Re: PIC16F1503 Fixed Voltage Reference

    the exact same wording is used in the PIC16F1829 datasheet yet that device DOES have the option to set the ADC Vref+ to the internal FVR module (ADPREF<1:0> = 11)

    Some consistency would be a good thing....

    Cheers
    Barry
    VK2XBP

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    Default Re: PIC16F1503 Fixed Voltage Reference

    Come on guy, Microchip can't even decide what to call basic registers. Hay hoo.
    George

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