> For the complete documentation index, see [llms.txt](https://docs.petoi.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.petoi.com/biboard/demo-applications/2.serial-port.md).

# 2.Serial port

There are 2 serial ports,which are separately located on 2 expansion sockets (P16, P17) ,on BiBoard.

The serial port 1 on the P16 can be connected to the USB downloader and  the external serial device.  Please do not use the downloader and the external serial device at the same time. The serial port voltage division will lead to communication errors.                           

In the Arduino demo, Serial represents the serial port 0, Serial1 represents the serial port 1.Serial and Serial1 send to each other.

```c
/* In this demo, we use Serial and Serial1 
*  Serial and Serial1 send to each other 
*/

void setup() {
  // initialize both serial ports:
  Serial.begin(115200);
  Serial1.begin(115200);
}

void loop() {
  // read from port 1, send to port 0:
  if (Serial1.available()) {
    int inByte = Serial1.read();
    Serial.write(inByte);
  }

  // read from port 0, send to port 1:
  if (Serial.available()) {
    int inByte = Serial.read();
    Serial1.write(inByte);
  }
}
```


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