Is it possible to perform a serial UART loopback test on NRF52832?

[Jinyue Zhu]

I am wondering if it's possible to conduct a serial UART loop back test on nRF. For example, if I use a wire to connect the TX and RX pins together, and send something out the TX, would the data come back in RX? If that is allowed, how do I test that in a windows environment? Should I use putty? Thanks.

Similar test: https://knowledge.ni.com/KnowledgeArticleDetails?id=kA03q000000YFtECAW&l=en-US

[awneil]

Jinyue Zhu said:

if I use a wire to connect the TX and RX pins together, and send something out the TX, would the data come back in RX?

Yes, of course it would!

However, if you're doing it on a Dev Board, be aware that the UART pins are connected to the interface chip which goes to the PC ...

An nRF52832 has only 1 UART - so, if you're doing a loopback test on that UART, you won't be able to use it to communicate with a PC.

[Jinyue Zhu]

Hi Awneil,

Thanks for the reply. If I am using nRF52832, then what should be the approach to verify the serial loopback actually worked...? Are there documentations in the datasheet that specify that the UART could support loopback?

Thanks,

Jinyue

[Sigurd]

Hi,

The UART example in the nRF5 SDK supports this, just set the define ENABLE_LOOPBACK_TEST

https://infocenter.nordicsemi.com/topic/sdk_nrf5_v17.0.2/uart_example.html

[Jinyue Zhu]

Hi Sigurd,

Thanks! Just out of curiosity, what would the behavior if I enable the loopback test? In this case, after I load the program to the board, no COM port can be used and hence how do I know the data flow back?

[awneil]

That's not a simple hardware connection, as you described in the OP.

In that example data sent from the PC is received by the nRF52 code, and that code then re-transmits it back to the PC:

    PC                     nRF52
  +-----+                +-------+
  |     |                |       |
  |     +---TX---------->+ ...   |
  |     |                |    :  |
  |     +<--RX-----------+....   |
  |     |                |       |
  +-----+                +-------+

This would be described as a software loopback.