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ESP32 S2
ESP32 S2 Technical Reference Manual
ESP32 S3
ESP32 S3 Technical Reference Manual
ESP32 C2 (ESP8684)
The ESP8684 is essentially the ESP32-C2 chip + flash embedded together in a single QFN package. Therefore the documentation for the ESP32-C2 is often titled as being for the ESP8684.
ESP32 C2 / ESP8684 Series Datasheet
ESP32 C2 / ESP8684 Technical Reference Manual
ESP32-C2 / ESP8684 Series SoC Errata