Serial ports on Opta

Official Hardware Opta
7

In the OPTA WiFi documentation, I found information that the AUX connector for the expansion module has RX and TX pins. I haven't figured out how to use them yet. If anyone knows which Serial it is, please help.
From what I understand, the connections marked in red are located on upper side, and those in blue are on lower side of the board.

I am also trying to connect a 3.3V TTL device (RX/TX) to the RS485 via a converter. I will let you know if I succeed.

schematic_aux
schematic_aux1258×740 51.2 KB

EDIT
I just discovered that AUX is Serial1 (UART 3V3), so you can read data using as simple code as follows:

void setup() {
  Serial.begin(9600);
  Serial1.begin(9600);
}

void loop() {
  if (Serial1.available() > 0) {
    char received = Serial1.read();
    Serial.print(received);
  }
}