ESP-01 AT Firmware AI-Thinker
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http://wiki.ai-thinker.com/_media/esp8266/ai-thinker_esp8266_at_firmware_dout_v1.5.4.1-a_20171130.rar Ai-Thinker_ESP8266_DOUT_8Mbit_v1.5.4.1-a_20171130.bin