UART peripheral of nRF52832 not disabled in System OFF mode?

[Remo]

Hi all

According to chapter 50.2 of the nRF52832 product specification V1.2, the pins used for the UART peripheral should be configured before in the GPIO peripheral to ensure correct behavior when the System OFF mode is entered.

Therefore I assumed that the UART peripheral (as all other peripherals) is disabled when the System OFF mode is entered and the previously set GPIO configuration takes effect.

We have configured the TX and RX signals as INPUT/DISCONNECTED to prevent from any cross currents when in System OFF mode, but the TX signals stays OUTPUT/HIGH!

When I disable the UART peripheral before entering the OFF mode, the pins are configured correctly. With the nRF51822, the behavior was as expected (pins were set to input/disconnected when OFF mode was entered).

Why is the UART peripheral not disabled in the OFF mode? Is this a bug in the nRF52832?

Kind regards

[Remo]

Can anyone from Nordic please reply?

[Stian Røed Hafskjold]

Hi,

The statement in the PS might be a bit confusing. It means that in order to avoid unpredictable behavior when the UART peripheral is disabled, the GPIOs must be configured as in the table, RX as input and TX as output. It does not mean that the GPIO configuration falls back to the previously configured values when the UART is disabled.

In order to have floating input pins in system off, you should first disable the UART peripheral and then configure the GPIOs as inputs before entering system off.

[Remo]

Thanks for your answer.

In this case the PS is not confusing but rather wrong, because it states explicitly that the pin configuration applies for the OFF mode:

To secure correct signal levels on the pins by the UART when the system is in OFF mode, the pins must be
configured in the GPIO peripheral as described in Pin configuration on page 532.

Will this be corrected in the PS? Why was this behavior changed from the nRF51 to the nRF52? Do all peripherals that need GPIOs behave the same way?

Kind regards

[Kenneth]

The pins will latch when entering system OFF, and direction and level depends on whatever might be controlling the pins at the time it goes to System OFF. The problem however is that when wakeup from System OFF, then all peripherals are reset, thereby the pins will fall-back to the GPIO configuration it had before going to System OFF. That is why we have a statement to make sure to configure the GPIO, to avoid that pins may switch direction or level after wakeup for a short period before init has been applied.

[Remo]

Thank you very much for the clarification.