RS232 Starting Transmission

FvM said:

Please show waveforms in readable size with time base information so we can interpret it.

The 'A' transmission example uses uncommon 7-O-1 (7 data bits, odd parity, 1 stop bit) format, also unusual right-to-left direction. Oscilloscope waveforms are always left-to-right.

'0' and '1' characters are normally send as ASCII codes 30 and 31 hex, using 10 bits in common 8-N-1 format (1 start bit, 8 data bits, 0 parity bits, 1 stop bit). The oscilloscope waveforms seem to extend over more than 10 or 11 bit times, it's not clearly what's exactly transmitted. My guess is three characters each, the number and carriage return + line feed. Would be much clearer if you send only one number character.

True, the code uses Serial.println(buttonState);, so carriage return + line feed are send along with 0/1.

--- Updated Oct 11, 2020 ---

You can use serial.print() instead of serial.println().

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int pushButton = 2;

// the setup routine runs once when you press reset:
void setup() {
  // initialize serial communication at 9600 bits per second:
  Serial.begin(9600);
  // make the pushbutton's pin an input:
  pinMode(pushButton, INPUT);
}

// the loop routine runs over and over again forever:
void loop() {
  Serial.print('1');
  delay(100);        // delay in between reads for stability

}

FvM said:

Fine, now it's a single RS232 8-N-1 frame, sent bits are 0 10001100 1.

1 start bit 0,
8 data bits for hex 31, starting with LSB
1 stop bit 1

--- Updated Oct 11, 2020 ---

Baud rate is 9600, bit time of 104 µs.

Click to expand...

FvM said:

Right. I'd however prefer hex notation 0x31 0x0d 0x0a because it can be directly translated to 4-bit nibbles and data bits.

Click to expand...

char data;
void setup() {
 Serial.begin(9600);
}

void loop() {
  if(Serial.available()){
    data = Serial.read();
    Serial.print(data);
  }
}

FvM said:

Serial.available becomes true when the stop bit is received. Retransmit is always delayed by 1 frame length.

Click to expand...