I want to connect two Arduino MEGA 2560, through Serial interface, in order to exchange data. My question is if Arduino_1 sends at the same time that Arduino_2 sends, will I have any collision so that data get mixed, and each Arduino gets unwanted mixed data?
UART serial communications are bidirectional, on two independent one directional lines.
Connect TX on one Arduino to RX on the other (and vice versa), as well as connect the grounds.
A Mega has three spare hardware serial sets, so don't use the normal TX/RX pins.
Leo..
Have a look at the 3rd example in Serial Input Basics and the parse example.
You can send data in a compatible format with code like this
Serial.print('<'); // start marker
Serial.print(value1);
Serial.print(','); // comma separator
Serial.print(value2);
Serial.println('>'); // end marker
...R