UART confusion in docs

Issue: Which UART to use - documentation has conflicting info

Setup: RAK4270 - in this case modules soldered to PCB’s but in general


It has been bought to my attention that the docs for the RAK4270 and its predecessor, the RAK4200 have conflicting information on which UART does what.

I have performed some tests but I’m somewhat confused, busy, tired and need to get absolute confirmation before I go to my certain death in relaying this information on.

Quick start shows connecting to UART1:

RAK4200 Data sheet pin configuration table shows UART2 and has UART1 shown as general GPIO or reserved:

RAK4270 Data sheet pin configuration table shows UART2 for AT commands and UART1 shown as AT commands and firmware updates:

The client had some RAK4200’s and was referring to the Data Sheet section when they did their PCB. They have now come unstuck with the first batch and junking the RAK4200’s and using RAK4270’s doesn’t seems to be a solution.

The breakout boards appear to have similar mixed up info.

I did originally ask about this back at the start of the year which is how they came to create a design that could accommodate both modules:

but I didn’t have any RAK4270’s to hand at the time so couldn’t do an absolute test and the pin mapping for the UART’s was the same so it all seemed good.

These modules are only going to be used as AT slaves but it would obviously be useful to be able to upgrade the firmware. As UART1 was shown as the main one on the RAK4200 they may have a pile of PCB’s that aren’t going to be upgradeable because despite being asked to, they didn’t provide any access to the SWD pins.

Could someone let me know which port is which and definitely does what please as that’s their current focus.

I can probably create some horrible bodged test pin holder to update the module prior to soldering so I may yet be able to survive the day intact!

Hi @nmcc ,

I think the confusion starts on the RAK4200 stating that UART1 as reserved (if I understand the situation correctly). How they did the connection in their RAK4200? I can’t visualize the issue yet because using either UART1 or UART2 for AT commands will both work. But for RAK DFU Tool FW upgrade, that is only possible in UART1 for both RAK4200 and 4270.

They went straight to the datasheet on the RAK4200 so wired up UART2 without checking etc. :man_shrugging:

Looking at the Quick Start and the Data Sheet, the average shows that UART1 is the preferable port as it allows FW updates. But I don’t have a RAK4270 break out to hand to test this. I’m happy to go with your greater knowledge.

With a bit of negotiation they can see that their users are never going to do a FM update but they want to update before they put them on the board. I see some laser cut acrylic & pogo pins in my near future.

I will update the RAK4200 docs to match the RAK4270 which is much clearer with the descriptions. I hope you can make a workaround on it with minimal effort.