Here’s a quick summary based on the chips used in the Xiao series:
- ESP32-C3:
The ESP32-C3 chip provides 2 hardware UART controllers. One is usually used for USB serial (the console), and the other is available for your own application. - ESP32-S3:
The ESP32-S3 chip also provides 2 hardware UART controllers. (Unlike the original ESP32, which had 3, the S3 – like the C3 – typically comes with 2.) - ESP32-C6:
The ESP32-C6 is a newer chip and is designed with a richer peripheral set. According to its datasheet, it provides 3 hardware UART controllers.
Keep in mind that while the chip may support these numbers, the actual board (the Xiao variant) may only expose a subset of them on headers depending on the design. However, these are the numbers available on the chip itself.