UART unresponsive on custom board

[pdpro]

I have designed a custom board using nRF52832. As per my understanding, we can configure any GPIO pin for UART communication. However, I am not able to configure the board for this communication.

I tried declaration of tx,rx,RTS,CTS using almost all spare pins, but there is no sign of UART communication successfully established. I tried to debug step by step and can see UART pins getting initialized and corresponding registers being assigned.

I am using nRF52840 for programming and debugging my target custom board through SWD. As a first step, I tried loop test on DK (shorting GPIO pin 6 & 8) and it is working fine, however my custom board doesn't have any exposed GPIO pin so I cannot do loop test. Please help me with UART on my custom board. Is there any special hardware connection arrangement needed for this communication?

[ovrebekk]

Hi Prasan

Can you provide a schematic for your board?
What are the UART pins connected to?

Are you able to connect a scope to the pins to see what is happening on the bus?

As you say there is no limit on which of the GPIO pins can be used for UART, as long as they are not used for anything else. 

Best regards
Torbjørn

[pdpro]

Hi Torbjorn,

There is some weird behaviour of board I observed today. As per general assumption, I changed the pin on nRF52840 DK to p1.03 & p1.05 as these are unused pins to check the behaviour of UART. I checked the schematic files also and these pins are not connected for any other interfacing. Unfortunately, there is no sign of communication happening on these pins, I cross-checked by connecting logic analyser also. 

I checked the schematic and found that pin P0.08 & P0.06 are connected through FSA2466UMX IC which is helping to see the communication through putty. This might be the reason that changing to any other pin is not working.

My custom board also doesn't have any pins hardwired for this communication. Please help me understand and resolve this issue.

Regards,

Prasan

[ovrebekk]

Hi Prasan

Sorry for the slow response, for the last month or so I have been out in travel and vacation. 

Is hardware flow control enabled?

If it is communication can only occur when both the RTS and CTS lines are low. 

It should be possible to re-assign the UART pins on the DK, even if the default configuration uses P0.08 and P0.06. 

If you can confirm whether or not HWFC is used I can run a test on my own to see if I spot the same issue. Could you share the main.c file of your modified example?

Best regards
Torbjørn

[ovrebekk]

Hi again

Ignore my comment with regards to flow control, I see now that you mention earlier that no flow control is used. 

If you can share the example code you test on the DK I will test it on my side to see where the problem might be. 

Best regards
Torbjørn