UART does not support odd parity

[wilusa]

We are building a prototype for a wireless solution using nRF52840 and we found that the UART included in this MCU does not support Odd parity. This is a major handicap that makes me reconsider whether this part is the right choice because the new design supposes to be plug and play with large install base that uses odd parity. I am still in shock and not believing that Nordic Semi made the UART that rigid, which triggers concerns about what other surprises I will be encountering later on. Honestly, I cannot recall any other MCU I have used that is missing this feature.
Is this one of those rare cases where MCU manufacturer has additional registers not exposed to users by default?
Can Nordic confirm that odd parity is not supported?

[Kenneth]

Hello,

Sorry, but we only support even parity: "When parity is enabled, the parity will be generated automatically from the even parity of TXD and RXD for transmission and reception respectively."

Best regards,
Kenneth

[Dmitry]

If your devices really check parity bit, I think the only way is to build a "semi-software" TX channel with SPIM peripheral - prepare a bitstream that include start/stop/parity bits and transmit it on MOSI output. It's not very difficult, and frequency generator is the same as in UART (value 0x1d60000 gives 115200 baud). For RX, you can just ignore parity error events.

[Kenneth]

I would like to mention that a colleague have worked on a UART implementation using SAADC (to sample RX) and PWM (to act as an TX), this should be able to do what you want:
https://devzone.nordicsemi.com/support-private/support/217709#permalink=412640 

[wilusa]

Hi Dmitry, thanks for your quick response. I was out of the office for a few days.

We were already considering what you are suggesting. We will try it soon.

[wilusa]

Hi Kenneth,

We will give it a try and let you know how it goes.

Thanks for your help.