HC-05 datasheet and How to enter the AT command mode
Datasheet : Download
AT Command Doc: Download
you have 2 way to enter the AT CMD mode:
Step 1: Input low level to PIN34->EN PIN. (it can also be floating)
Step 2: Supply power to the module.
Step 3: Input high level to the EN PIN(PIN34)(you can press the button this do this action,if you buy HC-05 from DSD TECH)
Then the module will enter to AT mode. The baud rate is as same as the communication time, default is 9600
Step 1: Connect PIN34(EN PIN) to the power supply PIN.or always press the button .
Step 2: Supply power to module
Then the module will enter to AT module. But at this time, the baudrate is always 38400. In this way, user should change the baud rate at the AT mode, if they forget the communication baud rate.