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Hot!Does RTCC pin output pulses when running on VBAT?

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jetrock
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2019/11/22 08:07:17 (permalink)
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Does RTCC pin output pulses when running on VBAT?

I haven't managed to find the answer to this anywhere. The datasheet for the RTCC says that the RTCC module runs when VBAT is supplying the chip. Does this include the RTCC pin as well (it's part of the RTCC module)? I assume it does and this means that I can put external hardware on the RTCC pin, set and alarm then shut down VCC and have the RTCC run on VBAT until the alarm triggers and have the RTCC pin then wake the processor up by turning VCC back on. Is that correct?
 
Regards
 
Andrew
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    mbrowning
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    Re: Does RTCC pin output pulses when running on VBAT? 2019/11/22 08:59:44 (permalink)
    +3 (3)
    Datasheet for what RTCC? I picked a random chip (MCP7940N) and the datasheet very clearly answers this question.
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    ric
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    Re: Does RTCC pin output pulses when running on VBAT? 2019/11/22 14:28:28 (permalink)
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    As this is in the "Peripherals" forum, the OP may well mean the RTCC peripheral inside a PIC.
    However as they have not revealed what device they are working with, we can only speculate.
     

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    jetrock
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    Re: Does RTCC pin output pulses when running on VBAT? 2019/11/23 06:10:38 (permalink)
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    I am indeed talking about the RTCC peripheral in a PIC. The chip I'm looking at is the PIC16F19156, but I dn't think that is particularly relevant as the same RTCC peripheral seems to be embedded in many PIC devices.
    I'll probably have to get a chip on the bench and see what happens in order to answer this. i still think the RTCC pin will output something when the alarm goes of as it is part of the RTCC module which is powered. Will the port peripheral multiplexing allow the signal to exit the chip on an actual pin though?
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    NKurzman
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    Re: Does RTCC pin output pulses when running on VBAT? 2019/11/23 10:03:54 (permalink)
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    “but I dn't think that is particularly relevant as the same RTCC peripheral seems to be embedded in many PIC devices.”
    You are wrong. Microchip has many different RTC implementations over the decades they made Microcontrolers.
    The fact that yours maybe used in many of the does not help.
    If you want answers, do not make people guess.
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    Mysil
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    Re: Does RTCC pin output pulses when running on VBAT? 2019/11/23 10:17:47 (permalink)
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    Hi,
    Many PICs have the same, or very similar RTCC,
    but very few have a Vbat circuit at all. 
    Of those devices that have Vbat, quite a few have serious Errata about Vbat operation.
     
    I would initially suspect that Vbat will power the secondary crystal oscillator and RTCC internal registers,
    and nothing else, when there is no Vdd available.
     
    For PIC32MK__GP/MC Family, Datasheet have this:
    RTCC Pin Output — Real-Time Clock Alarm/Seconds Output (not in VBAT power domain, requires VDD.
     
    But for that device family, there are other errata about Vbat.
     
    But why at all do you want to shut down power to PIC Vdd when there is power available for other external hardware to work? 
    The normal way to do what you want on a PIC microcontroller, would be to set PMD register bits for all peripherals that are not needed, set all I/O pins that are not used to output Low, set all outputs that are used such that they do not feed power out, unless you clearly want.
    Then make the PIC go into Sleep mode.
    You may then get PIC to wake up from RTCC interrupt, from Timer 1 interrupt, or from some other signals from outside.
     
        Mysil
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    jetrock
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    Re: Does RTCC pin output pulses when running on VBAT? 2019/11/23 13:40:45 (permalink)
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    The reason i want to shut VCC down is that I have a dc-dc converter generating it. I don't want that burning power while waiting for an alarm for what could be hours or days. Or years. There has to be a way to wake up, though. I may have to move to an external RTC or some other clock circuit to turn VCC back on.
     
     
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