Is it possible to invert the UART/UARTE logic in the nRF52832?

RE: Is it possible to invert the UART/UARTE logic in the nRF52832?

ovrebekk — Fri, 06 Sep 2019 06:44:05 GMT

Hi again

The PWM/SAADC UART implementation was shared in an older Devzone case if you're interested:
https://devzone.nordicsemi.com/f/nordic-q-a/40385/nrf52832-bit-band-uart-problem-19200-baudrate

Best regards
Torbjørn

RE: Is it possible to invert the UART/UARTE logic in the nRF52832?

ovrebekk — Thu, 05 Sep 2019 06:43:53 GMT

The method described by Dmitry is doable, but as he mentions it will affect current consumption quite a lot.

A while back there was a project in Nordic to implement an extra UART in the nRF52 using the PWM and SAADC modules. The PWM was used to generate the TX signal, by only using 0 or 100% duty cycle and matching the PWM update frequency to the baudrate. The SAADC was used to sample the RX.

Since both the PWM and SAADC use easyDMA they can run concurrently with the SoftDevice.

I will have to do some digging internally to see where the example was published and get back to you. If you only need to send data once in a while I think this driver should work fine.

Best regards
Torbjørn

RE: Is it possible to invert the UART/UARTE logic in the nRF52832?

Dmitry — Wed, 04 Sep 2019 09:28:18 GMT

If you have 4 free pins, you can try to create two "hardware inverters" inside 52832 with two pairs of GPIOTE channels - one will generate an event for low-to-high transition on input pin and trigger a CLR task for output pin, and vice-versa. Though I can't say how it will affect power consumption...

RE: Is it possible to invert the UART/UARTE logic in the nRF52832?

LoungingHound — Wed, 04 Sep 2019 05:37:12 GMT

OK I think a softdevice will still work for us. We have a very defined Transmit and Receive window, so unexpected interrupts are not going to occur. (We poll the peripheral and it responds, and while waiting for a response the processor only has two non critical monitoring tasks to complete). The problem with a hardware inversion is the increased power consumption, which then require additional hardware to shut down to sleep mode (we are working in the 5-10 uA range in sleep mode which is critical as this device can be running for many years on a single charge). This is going to add to the product cost and board real estate, both of which are very limited.

We did try some other work around's but each seems to cause other issues and we keep coming back to the same point.

Thanks for your feedback.

RE: Is it possible to invert the UART/UARTE logic in the nRF52832?

RK — Wed, 04 Sep 2019 04:20:22 GMT

No you can't invert it by changing configuration, the UART module only supports standard UART modes. Many, many people have bitbanged UART interfaces on the nRF series however you will have to deal, if you do it, with the softdevice interrupting you when you least want it. I'd just add a hardware inverter, by far the easiest way to accomplish this.