RS232 Starting Transmission

[imranahmed]

Please let me know I am learning RS232 Protocol I know many things about RS232 but stuck in thing. In simulation, I used Arduino UNO, Virtual Terminal and Oscilloscope and I am using Arduino Sketch 'DigitalReadSerial' but I want to know that when I send '1' it sends with start bit, data, stop bit but other bits are showing in oscilloscope what are them?
Please find attachment when I sent '1' and other is '0'.

Sending 'A' is an example but actually I sent '1' and '0'.

 

[FvM]

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().

 

[imranahmed]

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().

Ok. Now I am sending.
I

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]

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.

 

[imranahmed]

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.

Yes exactly means it is consists of start bit 8-data bits stop bit if we add println it will contain carriage return+line feed and it will display as in decimal
049 013 010

 

[FvM]

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

 

[imranahmed]

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

Ok good.
Thanks for helping.

--- Updated Oct 11, 2020 ---

Please let me know about delay in between receive and re-transmitted charater when I hit any character i.e 'a' , '3' or any the delay appers in between receive and re-transmitted delay why?

--- Updated Oct 11, 2020 ---

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

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

 

[FvM]

Serial.available doesn't become true before the stop bit is received. Thus retransmit is always delayed by 1 frame length, plus code execution delay.

 

[imranahmed]

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

I measured it is 1.1mSec delay.