And guess what : that was it :-)Originally Posted by Vicne
After checking all the connections once again, I discovered that ... I had put a wrong resistor value between GND and pin 4 of the optocoupler (see schematics) : 4K7 instead of the 1K I had calculated. I probably was too concentrated on positioning the components and picked up a wrong resistor that was laying around :-(
Anyway, I fixed that and made a 200km trip and back, and didn't have any link error. So the only think I'll remember is that the schematics and the software are OK :-)
Many thanks to all of you who helped me !