There are three serial ports on the ESP32 known as U0UXD, U1UXD and U2UXD all work at 3.3V TTL Level. There are three hardware supported serial interfaces on the ESP32 known as UART0, UART1 and UART2. Like all peripherals, the pins for the UARTs can be logically mapped to any of the available pins on the ESP32. However, the UARTs can also have direct access which marginally improves performance. The pin mapping table for this hardware assistance is as follows.

Having said that, the UART drivers that I recommend to use don’t have this level of optimization built into them and as a result, you are pretty much free to use any pins you choose. Continue reading ESP32 Hardware Serial2 Example →