I've been working on a rather pin constrained project with multiple serial ports. I've encoutered problems setting up some receive-only USARTS, as certain pins don't seem to work for this purpose.
I'm using a 64 pin device (ATSAMD51J19A). I've identified 4 pins which do not seem to seen by the USART peripheral (no data is received, no status changes or interrupts are issued).:
PA04 (SERCOM 0, IOSet 3, pad 0)
PA05 (SERCOM 0, IOSet 3, pad 1)
PB02 (SERCOM 5, IOSet 6, pad 0)
PB16 (SERCOM 5, IOSet 1, pad 0)
I've verified that when accessed through PORT GPIO, the signal is present and seen by the MCU on these pins. The pin MUX is performed after enabling the USART, and I've verified that the PINCFG/PMUX registers are correctly set.
Other pins in the same IOSets may work, e.g. PA06 (SERCOM0, IOSet 3, pad 2) and PB17 (SERCOM5, IOSet 1, pad 1) work fine. PB03 has other issues (MCU shows erratic behavior, hard faults or resets, when any external signal is applied to this pin, whether or not a USART is Muxed to it). I suspect the PB03 issue is a different one.
Any ideas as to what is going on? I've not seen anything which would explain this in the datasheet or errata?