I am asking how to enter from the data mode to the AT command mode without restarting and disconnecting any power supply. In other words, I am trying to make a driver to handle HC-05 module and now I have to switch between DATA mode to AT mode. When I try to switch backwards, it worls ( by putting off the EN pin and then send “AT+RESET” ) but from DATA mode to AT Mode I can’t reset the module. Anyhelp please ?

  • What Microcontroller do you use? You tagged both arduino uno and stm32 Commented Jun 1, 2021 at 17:11
  • old time modems used to have an escape sequence that caused the modem to drop out of data mode into command mode ... the sequence was +++ .... the HC-05 may have something similar .... though, I suspect that a hardware pin is involved
    – jsotola
    Commented Jun 1, 2021 at 18:10
  • @PythonSchlange I am using stm32
    – falcon_977
    Commented Jun 2, 2021 at 9:50

1 Answer 1


I am pretty certain there is no way to enter command mode from data mode without resetting the whole module. The only way to enter command mode is by setting the KEY pin high, and that pin is only read during the initialization phase of the module - and that means either a power cycle / reset, or a command-initiated reset.

You could either:

  • Provide a power control circuit which turns the module on and off (MOSFETs are good for this), or
  • Modify the module to attach a wire to pin 11, the RESET pin, and pulse that LOW to reset into command mode (I assume LOW, since that's the most common, though I haven't found anything to confirm it yet).
  • Thank you for your response. I think that the best solution is the first one and I will search about a MOSFET type that responds to my application. Best,
    – falcon_977
    Commented Jun 2, 2021 at 9:59

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