ESP-WROOM-02D integrates ESP8266EX chip for better RF performance
The ESP-WROOM-02 module is an IoT wireless module based on the ESP8266EX chip design. It integrates a TCP/IP network stack, a 32-bit low-power MCU, 10-bit precision ADC
with interfaces such as HSPI, UART, PWM, I2C, and I2S.
ESP-WROOM-S2 module 2 MB SPI Flash, connected to HSPI.
When operating as an SPI slave mode in SDIO, the transfer rate is up to 8 Mbps