The ESP8266 is a low-cost Wi-Fi chip with full TCP/IP stack and microcontroller capability produced by Shanghai-based Chinese manufacturer, Espressif Systems
The chip first came to the attention of western makers in August 2014 with the ESP-01 module, made by a third-party manufacturer, AI-Thinker. This small module allows microcontrollers to connect to a Wi-Fi network and make simple TCP/IP connections using Hayes-style commands. However, at the time there was almost no English-language documentation on the chip and the commands it accepted.
The very low price and the fact that there were very little external components on the module which suggests that it could eventually be very inexpensive in volume, attracted many hackers to explore the module, chip, and the software on it, as well as to translate the Chinese documentation.
In late October 2014, Espressif released a software development kit (SDK) that allowed the chip to be programmed, removing the need for a separate microcontroller.Since then, there have been many official SDK releases from Espressif; Espressif maintains two versions of the SDK — one that is based on RTOS and the other based on callbacks.
An alternative to Espressif’s official SDK is the open source esp-open-sdk that is based on the GCC toolchain. ESP8266 uses the Cadence Tensilica LX106 microcontroller and the GCC toolchain is open-sourced and maintained by Max Filippov. Another alternative is “Unofficial Development Kit” by Mikhail Grigorev.
32-bit RISC CPU: Tensilica Xtensa LX106 running at 80 MHz
64 KiB of instruction RAM, 96 KiB of data RAM
External QSPI flash – 512 KiB to 4 MiB (up to 16MiB is supported)
IEEE 802.11 b/g/n Wi-Fi
Integrated TR switch, balun, LNA, power amplifier and matching network
WEP or WPA/WPA2 authentication, or open networks
16 GPIO pins
I²S interfaces with DMA (sharing pins with GPIO)
UART on dedicated pins, plus a transmit-only UART can be enabled on GPIO2
1 10-bit ADC