The band if low-freq or high-freq is determined by PB12. There is an internal resistor in the module which the RUI3 firmware checks so it knows what frequencies it should allow. It is in the datasheet. Here’s the screenshot.
this was my problem on my pcb circuit…i forgot to make this pin VISIBLE 
Is there some work around ?
Hmm. I am not sure if we are in the same page here since you said VISIBLE.
The resistor is internal. It is inside the module so you won’t need to do anything.
However, if you mean you should have made it floating (not connected to anything) but it is connected to some parts of your circuit, then PCB cut trace is needed or remove the circuit affecting PB12.
i will have to cut the trace…
Well, one question…
That HEX that you sent me is the BOOTLOADER and at the same time a AT commands gateway…
My question is…is it possible to make a Arduino program on RAK3272 that only wait for the AT commands on UART ?
On Setup() i see that i have to put
Serial.begin(115200, RAK_AT_MODE);
But…on Loop()
What is must to put to only be a bridge of AT commands ?
void setup() {
// put your setup code here, to run once:
Serial.begin(115200);
Serial1.begin(115200, RAK_AT_MODE);
}
void loop() {
// put your main code here, to run repeatedly:
if (Serial.available() > 0) {
Serial.print(Serial1.read());
}
if (Serial1.available() > 0) {
Serial.print(Serial.read());
}
}?
is the 4.0.6 firmware already avaliable on ARDUINO API ?
one more question, RAK3272 has implemented on Arduino a low power 32 bits counter ? our need to sleep and wakeup to get the count ?
I don’t understand. Your Serial and Serial1 both accepts AT commands based on your code. What do you mean by bridge?
Not yet but it will be released soon once it is ready (basically after test and validation).
Same on your previous message, it is unclear what you want to achieve.
Sorry, i have type better the code.
The idea is the Arduino runs in BACKGROUND, and in the mains loop(), wait for AT COMMANDS in STM32 RX REAL SERIAL and transmit to the RX VIRTUAL SERIAL1 (Serial1.begin(115200, RAK_AT_MODE)).
When get the ANSWER from TX VIRTUAL SERIAL1, i forward this asnwer to the STM32 REAL TX SERIAL.
Why this, because i can run now on Setup() a pinMode INPUT_PULLUP on PB12, and when i send a AT+BAND command, it can runs, because will detects HIGH on PB12 
This is crazy
Arduino will have the same function of the AT commands engine, of hex that you send…but i can include the PULLUP pinMode to solve the pcb problem on my PB12