NFC pins configured as GPIO will short together

The NFC pins of my nRF52840 MCU have been set to be used as GPIO pins through the NFCPINS register. I can toggle the GPIO lines just but I find that after power on that the two NFC pins seem to be shorted internally together, for about 1 millisecond. How can I prevent this from happening because the NFC/GPIO pins drive some critical circuitry that can't tolerate the apparent 1ms pulse.

0 user75734 over 4 years ago

Hi

This sounds strange. Can you explain/show how you have configured the NFC pins as GPIOs exactly? What SDK and SDK version are you using for your project? For the nRF5 SDK the correct procedure is described in this case. Please note that if using the Development Kit you need to modify the DK with some extra resistors as explained in the DK user guide.

Also, please note that the NFC pins are not suited for high drive/freq. operations, and they are recommended to use at standard drive/low freq. in the pin assignments.

Best regards,

Simon
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0 user116799 over 4 years ago in reply to user75734
Thanks Simon,

We used the following code to configure the NFC pins as generic IOs.

NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Wen << NVMC_CONFIG_WEN_Pos; while (NRF_NVMC->READY == NVMC_READY_READY_Busy){} NRF_UICR->NFCPINS &= ~UICR_NFCPINS_PROTECT_Msk; while (NRF_NVMC->READY == NVMC_READY_READY_Busy){} NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Ren << NVMC_CONFIG_WEN_Pos; while (NRF_NVMC->READY == NVMC_READY_READY_Busy){} NVIC_SystemReset();

We hold the mcu reset pin and then provide the power to the hardware. We could capture a pulse which is in the following picture.

https://drive.google.com/file/d/1Sufa-ArswiFRmOJdXAPH-mhqfOxZ2j99/view?usp=sharing

Actually, we can get the same pulse even if we did not hold the reset pin.

And the versions of SDK / Softdevice are 7.0.1 and S140.
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0 user116797 over 4 years ago in reply to user116799

Futhermore, NFC1 is in configured as an input and pulled up with 100K to 3.3V and NFC2 is output to a 100K pulldown.
We are using the 15.3.0 SDK, I believe.
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0 user116799 over 4 years ago in reply to user116797

Thanks.
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0 user75734 over 4 years ago

Thank you for the update. Did you try configuring the NFC pins as GPIOs as explained in the case I linked to? It should be the correct procedure to do so for SDK v15.3.0.

If that doesn't help either, can you provide some more information on the following. Do you see this on one specific custom board or multiple ones? Are you able to recreate it on a Development Kit? Can you check what revision of the nRF52840 SoC you are using. What does the print on top of the nRF52840 SoC say?

Best regards,

Simon
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