ESP‐01
Dimensions: 14.3 x 24.8 mm
The bootloader can go into a number of modes depending on the state of GPIOs 0, 2 and 15. The two useful modes are the UART download mode (for flashing new firmware) and the flash startup mode (which boots from flash).
| Mode | GPIO0 | GPIO2 | GPIO15 |
|---|---|---|---|
| UART Download Mode (Programming) | 0 | 1 | 0 |
| Flash Startup (Normal) | 1 | 1 | 0 |
| SD-Card Boot | 0 | 0 | 1 |
CH_PD (or EN) Chip enable. Should be high for normal operation.
GPIO15 is connected to GND on ESP-01.
There are two version of ESP-01 module, the only difference is the size of the flash memory. The blue module has 512 Kb, and the black module has 1MB of flash:
