-
Dear Giovanni,
Serial 1 has higher protection resistances. When you use Serial 2 and it is working, we propose to use Serial 2. The other I/Os with lower impedances are SPI lines (be careful here because the SPI is shared), or you can use pins common with Outputs where is also protection impedance lower (for example Digital 1-5), but this can have influence to outputs. In general – serial 2 is the solution
.Jarda