Nrf Connect - uart for nrf52840 voltage level

[robert_lightbug]

Hello!

 Tyring to configure the uart rx/tx pins pull-up, pull-down or open-drain using the ncs 2.0.2 . So far I couldn't do it. For example "bias-pull-down" seems to have no effect and for open drain I was using "gpio_pin_configure()" after "uart_init()". Scope being: using the 3.3V uart levels nrf52840 to communicate with another chip at 1.8V level (just a last try before moving to a level shifter which needs to be added to the board, hence the mini-struggle to see if any way to avoid it).

Thank you!

[Simonr]

Hi

A UART application running at 3.3V won't be able to communicate with another UART device running at 1.8V, but the nRF52840 can run the entire SoC or the UART pins at 1.8V.

Please check out this ticket, where my colleague Priyanka explains how to set the GPIO voltage levels in the nRF Connect SDK. 

Best regards,

Simon

[robert_lightbug]

 Thank you, Simonr !

[robert_lightbug]

 One last thing, trying to be explicit: we have other chips that need the 3.3V, hence my question: is there any way of setting the uart tx/rx as open drain? I know if not the recommended way but is there a physical limitation or something else?

Thank you!

[Simonr]

Hi Robert

No, there's not a physical limitation as far as I know, but our UART driver will overwrite a pin set to for example open-drain. Please check out this case where using UART with an open drain is already discussed in more detail.

Best regards,

Simon

[robert_lightbug]

Thank you, much appreciated Simonr  !