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Benjamin Gao
Benjamin Gao
Associate II
February 11, 2017
Question

What shall i do with the NPOR pin in the stm32f0x8 line mcu?

  • February 11, 2017
  • 2 replies
  • 1634 views
Posted on February 11, 2017 at 19:26

Hi everyone!

In

RM0091 i was told that  the stm32f0x8 is some special, it's NPOR pin must be held low until VDD is stable, and when VDD is stable, the reset state can be exited either by putting the NPOR pin in high impedance.

Does this mean i should connect this pin pull down to GND, and wait for VDD stable, then set the reigster to make the pin high 

impedance? But how can the mcu knows VDD is on what status? Is there any other method to handle this pin?

Thanks~

Benjamin

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    2 replies

    Tesla DeLorean
    Tesla DeLorean
    Guru
    February 11, 2017
    Posted on February 11, 2017 at 22:57

    No it sounds like you need an external chip which externally clamps the pin low (open-collector) until the supply thresholds. Something like an MCP120

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    Benjamin Gao
    Benjamin GaoAuthor
    Associate II
    February 12, 2017
    Posted on February 12, 2017 at 03:24

    Hi Clive, the 

    MCP120 is exactly what i need, thanks a lot!

    ANURAG AKBARI
    ANURAG AKBARI
    Visitor II
    February 16, 2017
    Posted on February 16, 2017 at 20:27

    Can any one help me to understand NPOR pin feature in STM32F0x8 series. 

    What is the purpose of this pin and how to use this pin.

    I am new to stm32 series microcontroller.

    Tesla DeLorean
    Tesla DeLorean
    Guru
    February 16, 2017
    Posted on February 16, 2017 at 22:36

    Understand that the role of designer means you need to read and digest the technical documentation. In ST's case this would be the Data Sheet and Reference Manual.

    The part you are talking about is a 1.8V powered device, as such it doesn't have an internal POR (Power On Reset) circuit, you must provide this externally as part of your power supply design/strategy. Synchronous circuits need an effective reset circuit, this is not achieved with a simplistic R-C circuit, which is prone to fail under regular operating conditions, ie user initiated resets, or brief interrupt of supply. The latter can leave the chip in an indeterminate state.

    The NPOR signal is expected to clamp the pin to ground for a period of time after the supply (yours) has stabilized.

    The suggested circuit would be a laser trimmed MCP120 (or equivalent device) attached to VDDA and with something like a 10 or 47K pull-up to VDDA

    NPOR type inputs are NOT unique to STM32, but common over a lot of processors from the last several decades. The NRST and NPOR type pins should not be actively driven by push-pull drivers, or directly to supply pins.

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