The ESP-WROOM-S2 has hardware SPI speeds up to 8 Mbps and includes an ESP8266EX chip that integrates Tensilca L106 32-bit microcontroller (MCU) and a 16-bit RSIC. The system is able to support a Real Time Operating System (RTOS). The CPU clock speed is 80 MHz, but it is capable of reaching a maximum value of 160 MHz. The Wi-Fi stack only takes up about 20% of CPU time, and the remaining CPU time is available for user application. The other parts of the chip are able to work with the MCU through a variety of interfaces:

• The programmable RAM/ROM interface (iBus) can access the external flash by connecting to the memory controller.
• The AHB interface can access the register.
• The Data RAM interface (dBus) connects to the memory controller.

The memory controller is integrated within the ESP8266EX Wi-Fi SoC, which includes both SRAM and ROM. The MCU is capable of accessing this memory controller via dBus, iBus, and AHB interfaces. The RAM and ROM units can be accessed using these interfaces. The running sequence in the arrival order of requests is determined by a memory arbiter. The user program must be stored in the SPI flash integrated in this module because there is no programmable ROM on the chip. When the ESP8266EX is in Station mode and connects to the router, the available space in the Heap + Data sector is around 50 KB.

The support of SPI flash enables the ESP-WROOM-S2 to integrate 2 MB of SPI flash memory. In theory, the ESP8266EX could support up to 16 MB of SPI flash. It can support the Standard SPI, DOUT (Dual Output), DIO (Dual I/O), QIO (Quad I/O), and QOUT (Quad Output) SPI modes. In addition to this, this module utilizes a 26 MHz crystal oscillator that operates between -20°C to 85°C and has an accuracy of ±10 PPM.

Application areas include:

• Home automation and home security
• Smart lights and plugs
• Home appliances
• Sensors and detectors
• Security alarms
• Monitor and scales
• Mesh Networks
• Industrial Wireless Control
• Wearable Electronics
• WiFi Location-aware Devices
• WiFi Position System Beacons