RF HC-12, run AT commands by arduino

I have a HC-12 radiofrequency module that I tested and configured using a TTL USB converter, I now connected the HC-12 to the Arduino and I am not able to execute the AT commands and see the return, when it returns it shows this:
"f⸮⸮⸮ ⸮⸮? F? ⸮⸮ "

The code I’m testing is this:

#include <SoftwareSerial.h>

// serial antena
SoftwareSerial HC12(2, 3); // RX, TX

void setup() {

void loop() {
  while (HC12.available()) {        // If HC-12 has data
    Serial.write(HC12.read());      // Send the data to Serial monitor
  while (Serial.available()) {      // If Serial monitor has data
    HC12.write(Serial.read());      // Send that data to HC-12


How can I see the return of the AT command?


spycatcher2k: Does the module run at 19200 BAUD? Have you set your serial monitor to 19200 BAUD?

Yes, I have set this value for both.

Try 9600 for the baud rate for the HC-12.

Try 9600 for the baud rate for the HC-12.

I connected the hc-12 again in the TTL and executed the AT-RX command to see the settings and it returns this:

OK + B19200
OK + RC010
OK + RP: + 20dBm
OK + FU3

I think it should be working on the Arduino in 19200, right?
But anyway I changed to 9600, change the code and the terminal to 9600 and it worked, but I’m still in doubt as to why it did not work with 19200.