Serial Ports (USB and UART)

The Arduino-Pico core implements a software-based Serial-over-USB port using the USB ACM-CDC model to support a wide variety of operating systems.

Serial is the USB serial port, and while Serial.begin() does allow specifying a baud rate, this rate is ignored since it is USB-based. (Also be aware that this USB Serial port is responsible for resetting the RP2040 during the upload process, following the Arduino standard of 1200bps = reset to bootloader).

The RP2040 provides two hardware-based UARTS with configurable pin selection.

Serial1 is UART0, and Serial2 is UART1.

Configure their pins using the setXXX calls prior to calling begin()


The size of the receive FIFO may also be adjusted from the default 32 bytes by using the setFIFOSize call prior to calling begin()


The FIFO is normally handled via an interrupt, which reduced CPU load and makes it less likely to lose characters.

For applications where an IRQ driven serial port is not appropriate, use setPollingMode(true) before calling begin()


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

RP2040 Specific SerialUSB methods

void Serial.ignoreFlowControl(bool ignore)

In some cases, the target application will not assert the DTR virtual line, thus preventing writing operations to succeed.

For this reason, the SerialUSB::ignoreFlowControl() method disables the connection’s state verification, enabling the program to write on the port, even though the data might be lost.