It's of course backwards compatible with existing Arduino add-ons, but sets itself apart with a new USB controller with lower latency and driver-free operation on Mac and Linux.

In it, he shows an example of using all three ESP32 UARTs from an Arduino program. He calls the third port “secret” although that’s really a misnomer.

Introduction:In Arduino environment, it's convenient to access BT SPP like a serial port and react to the command string sent from the BT serial port. Many Arduino projects have utilized this way ...

The write code also can detect an I/O port write and sends that data to the Arduino serial port. It doesn’t appear to matter what I/O port you write to.