The RTC module is specifically designed for Raspberry Pi. It communicated with Raspberry Pi through I2C bus. There is a Maxim DS1307 and CR1220 button cell on the board to keep the real time for a long time after the Raspberry Pi has its power down. Set a serial port, TTL convenient way online debugging.
This is the pin compatible upgrded version of the ESP-01 chip.
ESP8266 is a highly integrated chip designed for the needs of a new connected world. It offers a complete and self-contained Wi-Fi networking solution, allowing it to either host the application or to offload all Wi-Fi networking functions from another application processor.