ESP8266

ESP8266=ESP8089

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ESP8266 is its own clone of Espressif Systems ESP8089 released back in 2012 and without any modifications it is still sold by Espressif with the inscription "ESP8266". The programs in the ROM chip are designed for 40 MHz quartz. The crystal was designed to connect via SDIO as a WiFi adapter. “ESP8089” is proudly written on the crystal itself, and “ESP8266” is written on the plastic case.

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https://hackaday.io/project/8678-rpi-wifi