Are TX and RX LEDs supposed to blink when transmitting?

Hello every one,
I juste purchased an Arduino UNO R4 Minima, and I am wondering why TX and RX LEDs on the board are not blinking when Serial transmission is on?
On my Arduino UNO R3 board, they worked very fine, but not on my R4 Minima.
I tested the two LED with the following Sketch on my UNO R4 Minima, and they worked:

void setup() {
pinMode(22, OUTPUT); // Use 21 for TX LED.
}
void loop() {
digitalWrite(22, HIGH);
delay(1000);
digitalWrite(22, LOW);
delay(1000);
}

So, I concluded that it is not a LED problem.
Could anyone tell me if these two LEDs are supposed to blink when transmitting Serial data via USB cable?
Thank you in advance

I don't know your board, but if it has native usb, it probably doesn't use serial pins for usb.

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The Minima uses native USB. You won't see the Tx-Rx lights.

I think it would be possible to use an event link to turn the pin on whenever the transmit register gets loaded, but I don't know that it would be easy.

On the R4 the ESP32 serves as a serial bridge and the Tx-Rx lights on it work like they do on the R3.

1 Like

Thank you a lot for your answers.
Could you explain to me what is the meaning of "native USB"?
Why do TX and RX LEDs blink on UNO R3 board, and not on UNO R4 Minima board? (they both communicate with the PC using USB cable)?

Your Uno R3 has a separate serial-to-usb converter to provide USB connectivity with the PC; it is connected to the UART of the main processor (328P).

In case of boards with native USB, the USB connectivity is provided by the main processor itself.

They are driven by the serial-to-USB converter, not by the 328P.

That might be the case for the R4 minima; I don't have the board so I can't verify. It however is not the case for e.g. an Arduino Micro.

Do you want the truth? ...

... simply because whoever developed the driver for the ATmega16U2, which is present on the Arduino UNO R3 as a USB <-> Serial converter, spent time developing support for handling the two LEDs (just look in the firmware sources to find it all in the files Arduino-usbserial.c and Arduino-usbserial.h), while the same thing was NOT done by whoever developed the USB part of the Arduino UNO R4. :confused:

Guglielmo