Connect Uno and serial port on my computer.

Hello,

I'am a new user of Arduino Uno and i am french...two difficulties :wink:
I am trying to use SoftwareSerial. I have connected Tx and Rx of my computer to digital I/O 10 and 11 of my Uno. Only that.
My Uno is on usb port (/dev/ttyACM0) and my I/O serial on my computer is /dev/ttyS0.
Here is the code :

#include <SoftwareSerial.h> 
SoftwareSerial PortSeriePortable(10,11);
void setup(){
        Serial.begin(9600);
        Serial.println("Salut le PC de bureau !");
        PortSeriePortable.begin(9600);
        PortSeriePortable.println("Salut le portable !");
}       
void loop(){
        if(PortSeriePortable.available())
                Serial.write(PortSeriePortable.read());
        if(Serial.available())
                PortSeriePortable.write(Serial.read());
}

The problem is that the second message never print on PortSeriePortable.
I have opened two terminals : one for /dev/ttyACM0 and one for /dev/ttyS0.
When i write a 'a' on one terminal, the second reads another character.
Is there something wrong with the connections (or something missing ?).
Thank you very much.

P.S. : i just have seen that it is necesseray to connect a dual driver/receiver between (type MAX232)...

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