Hi there,
So, this should address it 
Yes, absolutely — you can reassign almost any GPIO on the XIAO nRF52840 for SPI, I²C, UART, or GPIO as long as the function is supported by the hardware peripheral mux (Pin Function Mapping).
The Nordic nRF52840’s GPIO matrix is flexible: you can route the SERCOM peripherals (SPI, I²C, UART) to most pins by reconfiguring them in software. This is part of what makes the chip so adaptable.
However — and this is the important caveat — not all pin remaps give you identical electrical or performance behavior.
For example:
- I²C: Only certain pins support hardware pull-ups or the high-drive modes expected for stable I²C at 400 kHz or higher. Moving SDA/SCL to random pins may require stronger external pull-ups or lower speed.
- SPI: You can relocate MISO/MOSI/SCK/NSS, but drive strength, timing, or interference might vary because of board routing. Some pins share internal connections with the QSPI flash or NFC, and reassigning them can break other functions.
- UART: TX/RX can be mapped freely, but hardware flow-control (RTS/CTS) only works on specific pins.
Bottom line:
You can absolutely assign alternate GPIOs for SPI/I²C/UART, but you may lose optimized hardware features, and the routing or power domain might not be ideal. On compact boards like the XIAO, the default pin mappings are chosen to balance performance, signal integrity, and power draw.
That’s the “truth-in-engineering” way to put it: yes, flexible — but not all configurations are equal.
HTH
GL PJ 