When the ESP-01 first appeared on markets like eBay and AliExpress around 2014, it was essentially a "black box". The initial datasheets were primarily in Chinese, and the module was marketed as a simple . It was intended to be a cheap accessory that gave an Arduino internet access via AT commands. 2. The Great Revelation
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To make the ESP-01 usable, you also read: esp01 datasheet
The datasheet mentions GPIO0 and GPIO2 but does provide the definitive boot mode table: When the ESP-01 first appeared on markets like
The table is solid and critical for survival: esp01 datasheet