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I have an ESP-01 chip. I found out that I need to ground the GP0 pin to enter the programming mode to flash a program to the chip. I can't find anything in the ESP8266 datasheet that documents this. I'm wondering how we know that we need to ground this pin to be able to program the ESP.

kovac
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    https://www.espressif.com/sites/default/files/documentation/esp8266-sdk_application_note_firmware_download_protocol_en.pdf – Juraj Apr 30 '23 at 10:13

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Try pressing CTRL-F in the PDF reader and find for words "BOOT" or "GPIO0".

On page 11 it finds this:

GPIO2, GPIO0, and MTDO are used to select booting mode and the SDIO mode

Justme
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  • Could you explain a bit more on how to interpret this? "select" here refers to grounding? And this means I can ground GP2 instead of GP0 or ground both and I enter booting mode? – kovac Apr 29 '23 at 09:46
  • No, these pins all together select in which mode to boot up the chip, from where it starts loading code for execution. These strap pins default to some value, either weakly pulled up or down by the chip itself, or pulled up or down by resistors on the module or PCB where the chip is mounted. If you try to externally use this pin for some purpose, it may disturb the startup boot selection purpose. The list of how these pins select the boot mode must be somewhere in the datasheet or other documentation. It's no secret. – Justme Apr 29 '23 at 12:47