The HC-12 manual says, When the second method (pin 5 “SET” tied to ground before power is applied), the module always enters command mode with the serial port configured for 9600bps, 8 data bits, no parity, 1 stop bit, irrespective of any previously configured settings. I tried to get 3 or 4 of my HC-12s to reset to the DEFAULT settings by powering up with "SET" held low, but my versions would not reset.
