“SoftwareSerial” PIO-based UART — Arduino-Pico 3.1.1 documentation

Equivalent to the Arduino SoftwareSerial library, an emulated UART using
one or two PIO state machines is included in the Arduino-Pico core. This
allows for up to 4 bidirectional or up to 8 unidirectional serial ports to
be run from the RP2040 without requiring additional CPU resources.

Instantiate a SerialPIO(txpin, rxpin, fifosize) object in your sketch and then
use it the same as any other serial port. Even, odd, and no parity modes
are supported, as well as data sizes from 5- to 8-bits. Fifosize, if not
specified, defaults to 32 bytes.

To instantiate only a serial transmit or receive unit, pass in
SerialPIO::NOPIN as the txpin or rxpin.

For example, to make a transmit-only port on GP16
.. code:: cpp

SerialPIO transmitter( 16, SerialPIO::NOPIN );

For detailed information about the Serial ports, see the
Arduino Serial Reference .