Use of PA13 SWDIO PA14 SWCLK

LPWAN Modules / EVBs RAK3172
#1

Hello again RAKWireless…

For RAK3172, Your Documentation says not to use:
|PA13|SWDIO|
|PA14|SWCLK|

In developing Stand Alone firmware with Arduino, what is the negative issue with using these specific pins?
I ask because I have a run of PCB’s that has a port shown below:
image

I am thinking of using this to add an external WDT daughter board until internal WDT is working…
Thanks

#2

Hi @pmjackson ,

The idea of not using the SWD pins is its availability in the future for firmware update and debugging. It is a good practice I see in many designs. However, it doesn’t mean it needs to be in a header. Even SWD testpoints for pogo pins is sometimes enough. If you need that space for external watchdog, you can probably use that area and just make test points for the SWD pins.

#3

Thanks Carl.
I understand what you are saying.

I already have 50 prototype boards in production that have this port already.
My question is really for a temporary use case for the current 3.5.3 RUI3.

Since I already have this port, I am thinking of a small plugin WDT board to that header port.

I would just need one I/O from RAK3172 to reset the ext. WD. The power and reset are there too.

It would make it simpler for me to add a small plugin external WDT

#4

I tested both PA13 and PA14 on 3.5.3 and it works fine. If you are not using the pins for debugging, I believe using it a reset pin for the external watchdog won’t give any harm.

Those pins have alternate functions as well. The datasheet doesn’t have any note or warning on not using it as IO.

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#5

Thanks Carl.

That is good news. I wasn’t sure of all of RUI3’s pin usage.

#6

Extra caution on PB12 since there is an internal resistor in it.

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#7

Thanks for the pointers…