Hi,
I have been struggling with making XIAO RP2040 work with a MAX232 chip. But there is a design mistake on the board, and I can only use D1 as RX while D2 as TX pin 
Is it possible to CHANGE pinouts for built-in UART hosts? Or can I use something like software serials on XIAO RP2040?
Thanks a lot.
The RP2040 Data Sheet shows that UART0 (the one used by Serial1 on XIAO RP2040 pins D6 and D7) could be assigned to GPIO28 and GPIO29 (by writing directly to certain registers not in the Arduino paradigm ). GPIO28 and GPIO29 are connected to XIAO RP2040 Pins D2 and D3, but there is no way to connect a UART to GPIO27 and GPIO28. Period. Full stop.
You can try it, but whether it works satisfactorially or not is always a big question mark.
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Some have reported success, but I, personally, would not release a product with software serial unless it was absolutely necessary. I will say that using software serial to keep from having to modify a board would not be considered absolutely necessary by anyone I have ever worked for. YMMV (Your Mileage May Vary.)
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Regards,
Dave
Footnote: Of course, if you are not using D6 and D7 for anything else, you could just jumper to D2 and D1, respectively, but I am always out of pins on little things like XIAOs.