ESP‐01 - lvidarte/esp8266 GitHub Wiki

Dimensions: 14.3 x 24.8 mm

ESP-01 Pinout

ESP8266 Bootloader Modes

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.

Wiring the ESP-01 with only a CP2102 (Programming Mode)

ESP-01 Models

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: