know when UART serial data has been sent

[tomshirvo]

Hi All,

I'm using a max481E RS485 chip with a few Arduinos connected. This chip needs two pins changed to allow sending or receiving. The problem is that I have made a function that will set the pin then send the data and then change the pin back. Only one character is sent and the pin is set back to LOW. I think this is because the serial.write is shifting data into a buffer and then the hardware for the serial takes over and sends it.

Is there a way to know when the data is sent or wait until the data is sent and then change the pin state.

Code: [Select]

void commWrite(char * data,int dataSize){
  digitalWrite(commsTX,HIGH);
  for(int i = 0; i < dataSize;i++){
    Serial.write(data[i]);
  }
  digitalWrite(commsTX,LOW);
}
Thanks

[westfw]

In theory, on AVR you can check the TXC0 bit in the status register, and this is done by the Serial.flush() arduino function.
(In practice, there are some complications and I'm not sure whether they ever got it working perfectly.  But that's the starting point.)

[tomshirvo]

Thanks for that, I just added Serial.flush() as that waits until the data has been sent before returning.

Code: [Select]

void commWrite(char * data,int dataSize){
  digitalWrite(commsTX,HIGH);
  for(int i = 0; i < dataSize;i++){
    Serial.write(data[i]);
  }
  Serial.flush();
  digitalWrite(commsTX,LOW);
}