Equipped with 3 LEDs: TXD LED, POWER LED TXD: using bent pin Used to computers with microcontrollers, module, and other devices to achieve functions such as data transmission, program download, and debugging. Supports 3 power supply: 5V external power supply; 3.3V external power supply; Power by external sources (3.3V-5V required). Other function PIN: Reserved solder pad (for distribution pin, inserted up or down to access the user; PIN spacing supports insertion into board). Attention: This product not come with a USB cable. This module is converted from USB. Do not directly to avoid burning out the module.