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[on:]

Hi all !

Firstly excuse me for my bad english..

I have a little problem, i programmed my arduinio nano v3 with mini USB and my program work normaly but only when i use the USB connection ( integrated in the arduino, i have just to put my USB wire ).

My application is a compass who are connected at the arduino with i²c bus, and arduino give me 3 values like : "33 -66 34"; with usb connection i have no problem but with RS232 connection ( Tx, Rx and ground ) the response are like : x97\x00\xab\x2e\xac\x66\xga\xab....... ; And with RS232 connection i can't update my arduino

Tha data rate are corectly configured, flow control also..

Do you know what is the problem ?

[Reply #1 on:]

If you are trying to connect RS232 to the RX/TX lines, you need to invert them.
RS232 use a High level to indicate nothing is going on, then a Low indicates a Start Bit has occured and data is starting.

The Aruino Rx/Tx lines use a Low level when nothing is going on, and Start Bit goes high.

So you need to invert the levels.

[Reply #2 on:]

Thank you for your reply.

But RS232 have just 1 protocol ? no ? i knew a problem could be the high logic level TTL or 3.3v but arduino give a high level TTL and it's the first time i hear this problem...

So i will try it, do you know any components who can do it ?

thanks a lot !

[Reply #3 on:]

The Aruino Rx/Tx lines use a Low level when nothing is going on, and Start Bit goes high.

I believe you have that backwards. TTL serial uses true logic, a data bit is true high and a stop bit is equal to a data bit high and a start bit is equal to a data bit low, so the idle condition ("nothing going on") on a serial link is at a continous high (stop condition) waiting for the next start bit low.

Lefty

[Reply #4 on:]

Lefty,
I'm gonna have to pull out myscope & check again.
Maybe the device I was talking to was putting out TTL serial (low = nothing happening) and I had to invert coming in to see good data. I had worked that out last August.
Robert

[Reply #5 on:]

Lefty,
I'm gonna have to pull out myscope & check again.
Maybe the device I was talking to was putting out TTL serial (low = nothing happening) and I had to invert coming in to see good data. I had worked that out last August.
Robert

Yes, one can once and awhile come across something using non-standard inverted logic. But standard TTL is as I stated. Simple test with just a voltmeter on the txd pin after loading this simple sketch. You will see the output is almost always +5vdc on both the send and receive arduino pins, as it's only sending one character every two seconds.

Code:

/*
  Blink
  Turns on an LED on for one second, then off for one second, repeatedly.
 
  This example code is in the public domain.
 */

void setup() {               
  // initialize the digital pin as an output.
  // Pin 13 has an LED connected on most Arduino boards:
  pinMode(13, OUTPUT);
  Serial.begin(9600);
 
}

void loop() {
  digitalWrite(13, HIGH);   // set the LED on
  delay(1000);  // wait for a second
  Serial.println("?");
  digitalWrite(13, LOW);    // set the LED off
  delay(1000);              // wait for a second
}

Lefty