UART is TTL or RS232?

 

UART (Universal Asynchronous Receiver/Transmitter) is technically neither; it is the logic protocol itself, but it almost always operates at TTL levels (\(0V\)-\(3.3V/5V\)) inside microcontrollers. It produces raw data, which can then be transmitted via TTL or converted to RS-232 (\(+12V\) to \(-12V\)) for long-distance industrial communication. [1, 2, 3, 4, 5]

Key Differences:

• UART (TTL): Used on microcontrollers (Arduino, STM32) and sensors. Idle state is HIGH (\(3.3V/5V\)), and active is LOW (\(0V\)).
• RS-232: Used on older PCs and industrial equipment. Uses high bipolar voltages (e.g., \(\pm 12V\)) for long distances and noise immunity.
• Compatibility: You must use a MAX232 level shifter to connect a TTL UART to an RS-232 device.
• TTL UART (0–Vcc, e.g., 3.3V) is for short-distance communication on a single board.
• RS-232 (\(\pm 3V\) to \(\pm 15V\)) is for long-distance, industrial, or legacy communication. [1, 2, 3, 4, 5, 6]

Important: Never connect a TTL UART directly to an RS-232 port, as the higher voltages can damage your microcontroller

Arduino to Arduino UART

 https://peppe8o.com/arduino-uart-communication/

 

 

 

 

 

Section 1: “uart-trasmitter-code.ino” code

This section contains the code explanation for the transmitter, which performs Serial.write(x). The x is the value that reads from the push button. The push button, when pressed, becomes high, which means that it becomes 1. The baud rate set for the communication is 9600. The LEDs are set here to get the value from the receiver to turn the LED on and off.

#define PB 2
void setup()
{
  Serial.begin(9600);
  pinMode(13, OUTPUT);
  pinMode(PB, INPUT);
}
void loop()
{ byte x=digitalRead(PB);
  Serial.write(x);
  if(Serial.available())
  {
  byte rec=Serial.read();
  if(rec==1)
  {
    digitalWrite(13,HIGH);
  }    
  else digitalWrite(13,LOW);
  }
}

Section 2: “uart-receiver-code.ino” code

This is the section for the receiving part. Both the receiving and transmitting codes look the same as the communication is happening in half-duplex. So the commands send from the transmitter and received at the receiver by the serial.read() if the value is 1, then the LED turns on; otherwise, it remains off.

#define PB 2
void setup()
{
  Serial.begin(9600);
  pinMode(13, OUTPUT);
  pinMode(PB, INPUT);
}
void loop()
{ byte x=digitalRead(PB);
  Serial.write(x);
  if(Serial.available())
  {
  byte rec=Serial.read();
  if(rec==1)
  {
    digitalWrite(13,HIGH);
  }    
  else digitalWrite(13,LOW);
  }
}

Simulating the Arduino UART communication

The simulation is made to give the demo, as in the picture it can be seen that the led on the receiver side is on, which happened by pressing the button at the transmitter. Similarly, the second figure, displays that LED is on the transmitter side, in which the button at the receiver is pressed. On pressing the button, the value becomes 1, which means that the transmitted value is 1, while without pressing the button, the value is 0.

What’s Next

Please find more tutorials on Arduino in peppe8o Arduino archives.

Enjoy!

Umar Jamil

For any queries and help for work, please contact me at:
Whatsapp: +92-346-661-7017/ Link
Email: umarjamil0007@gmail.com

Umar Jamil (Umar Jamil)