TXD: the sending end , generally expressed as their transmitter, normal communication must be connected to RXD another device . TXD: the sending end , generally expressed as their transmitter, normal communication must be connected to RXD another device . Collected spontaneously : RXD when normal communication to other devices connected TXD, so if you want to receive data transmitted by its own name suggests , it is their own to receive data transmitted , which is directly connected to its own TXD RXD, use 1. the core module using the HC-06, interface includes VCC, GND,TXD,RXD, aside LED status output pin, the microcontroller can be connected via Bluetooth to determine whether the pin state, KEY pin of the slave invalid 2. led indicate Bluetooth connection