Tag Archives: esp12

Restoring the AT firmware on the ESP8266

Most of the time I am using Wemos D1 mini development boards in combination with the Arduino IDE to make my own firmware to run directly on the ESP8266 chip. But I also have some bare ESP-01 and ESP-12 modules lying around, and recently I came up with the plan to use one of them.

The specific project requires very well controlled timing of an ADC, for which I will use a regular ATmega328P-based Arduino board. In this project the ESP8266 will only be used to transmit the data over WiFi. Neither my ESP-01, not my ESP-12 still have the original AT firmware, since I have been experimenting with various other firmwares.

This is where the challenge starts, since my plan required restoring my ESP-12 to the AT firmware and use a library like ESP8266wifi or WiFiEsp. I realize that I have been struggling with different firmwares before, hence this post to give a short review and to keep some notes for my own future reference.

Module form factor

The ESP8266 microchip comes on various development boards that include an USB interface, such as the Wemos D1 Mini and the NodeMCU board, but also as bare modules such as the ESP-01, 02, etc. This page on the ESP8266 wiki has an overview of all modules and this page has comparison of some of the raw modules with some of the development boards.

ESP-01 module:

ESP-12 module:

Flash memory capacity

Besides the number of GPIO pins that is exposed by each of the modules, another important feature is their flash memory capacity. The AI-Thinker website has a module list table that includes this. The ESP-01 module comes with 4Mbit, i.e. 1MB of flash. The ESP-12 module comes with 4MB. Note that there are development boards such as the Wemos D1 mini pro that even have more.


As the ESP8266 is nowadays fully supported in the Arduino IDE, I prefer to develop my own custom firmware for the ESP8266 using C/C++ and the Arduino IDE and libraries. So the most confusing aspect of the ESP8266 for me is that there are multiple “standard” firmwares available for it, which I often accidentally confuse. These include

  • The AT firmware, comparable to the Hayes command set on old modems.
  • The NodeMCU firmware, which includes a LUA interpreter.
  • The MicroPython firmware, which includes a Python interpreter.
  • The Espruino firmware, which includes a JavaScript interpreter.

For the firmware options that include a Python or a JavaScript interpreter it should be mentioned that there are other versions from other companies/projects.

The NodeMCU project is more centrally managed/organized and includes a website where you can compile customized firmwares with support for specific hardware add-ons.

Restoring the AT firmware

To flash the firmware to an ESP8266, you will need to wire it up and get it in the right boot loader mode. There are many online tutorials for this and I won’t elaborate here. You will also need software to write the new firmware, I am exclusively using esptool.py.

I tried various options to flash my ESP-12 with the original firmware, most of which failed. The challenge is to figure out which firmware is compatible with my specific module, and to which flash memory locations to write the different pieces of the firmware. In the next section I will describe three things that worked, going from the oldest to most recent firmware versions.

Following the instructions here and using a rather obscure version of the firmware contained in a single binary file from here, I had success with:

esptool.py --port /dev/tty.usbserial-FTG54BPS --baud 115200 write_flash --flash_mode dio 0x00000 v0.9.2.2\ AT\ Firmware.bin

Subsequently I was able to connect in a terminal program with 9600 bps and got

[System Ready, Vendor:www.ai-thinker.com]



Using the old AT firmware from Espressif itself with the “Offical ESP8266 AT+ Commands” from their old GitHub repository I was also able to get it to work with:

esptool.py --port /dev/tty.usbserial-FTG54BPS --baud 115200 write_flash --flash_mode dio 0x00000 boot_v1.1.bin
esptool.py --port /dev/tty.usbserial-FTG54BPS --baud 115200 write_flash --flash_mode dio 0x01000 newest/user1.bin
esptool.py --port /dev/tty.usbserial-FTG54BPS --baud 115200 write_flash --flash_mode dio 0x7C000 esp_init_data_default.bin
esptool.py --port /dev/tty.usbserial-FTG54BPS --baud 115200 write_flash --flash_mode dio 0x7E000 blank.bin

Subsequently I was able to connect in a terminal program with 115200 bps and got




The Espressif ESP8266 SDK Getting Started Guide contains the most recent information about the layout of the flash memory. Using the 2.2.1 release from the Espressif NONOS_SDK repository and

esptool.py --port /dev/tty.usbserial-FTG54BPS --baud 115200 write_flash --flash_mode dio 0x00000 boot_v1.2.bin
esptool.py --port /dev/tty.usbserial-FTG54BPS --baud 115200 write_flash --flash_mode dio 0x01000 at/512+512/user1.1024.new.2.bin
esptool.py --port /dev/tty.usbserial-FTG54BPS --baud 115200 write_flash --flash_mode dio 0x7C000 esp_init_data_default_v05.bin
esptool.py --port /dev/tty.usbserial-FTG54BPS --baud 115200 write_flash --flash_mode dio 0x7E000 blank.bin

I also had success and was able to connect in a terminal program with 115200 bps. This resulted in the following response

AT version: 13 2018 11:10:59)
SDK version:2.2.1(6ab97e9)
compile time:Jun 7 2018 19:34:26
Bin version(Wroom 02):1.6.2

I did not have success with the 3.0 release from the Espressif NONOS_SDK repository. That one does not have the “512+512” directory, only the “1024+1024” directory, which I could not get to work on my ESP-12. Suggestions to make this work are welcome.

ESP-12 bootloader modes and GPIO state at startup

Since I encountered some initial difficulties in programming the ESP-12 version of the ESP8266 module using the Arduino IDE, let me here summarise some findings based on information from [1,2,3].


The ESP-12 module exposes 11 GPIOs. Three of them are especially relevant, as they determine the bootloader mode at startup or following reset.

                                  | GPIO 0 | GPIO 2 | GPIO 15
Flash Startup (Normal)            |   1    |   1    |   0
UART Download Mode (Programming)  |   0    |   1    |   0
SD-Card Boot                      |   0    |   0    |   1

Furthermore, CHPD should be pulled up and RESET should be pulled up or should be floating. If you connect RESET to ground, the module resets.

I have not yet figured out what the SD-Card boot means, so in my applications GPIO 2 should always be pulled up and GPIO 15 should always be pulled down. I am using 10k resistors, but smaller values (e.g. 3.3k) should also work.

To facilitate development, I connected two push button switches to the GPIO 0 and RESET pins, shorting them to ground when pressed. When the buttons are not pressed, they are both pulled up to 3.3V using a 10k resistor.

This allows me to do the following two-finger-action to restart in programming mode and allow the Arduino IDE to upload a new firmware:
– press reset button
– press programming button
– release reset button
– release programming button


[1] https://zoetrope.io/tech-blog/esp8266-bootloader-modes-and-gpio-state-startup
[2] http://www.instructables.com/id/Getting-Started-with-the-ESP8266-ESP-12/
[3] http://www.instructables.com/id/ESP8266-Using-GPIO0-GPIO2-as-inputs/