The document describes the AT command set for the HC-03/05 embedded Bluetooth serial communication module. It has two main modes - order-response mode and automatic connection mode, with three roles in automatic connection mode: Master, Slave, and Loopback. The module's mode can be switched by controlling the PIO11 pin level. It provides various AT commands to control parameters like role, address, name, baud rate. Commands need to end with a terminator. PIO pins have functions like controlling the LED and reset.