@ricardocrudo Thank you for the reply!
I will elaborate on my thoughts and questions a bit.
I interpret the schematic as follows:
rj45 pin: arduino(mcu)
1: Arduino tx pin
2: Arduino tx pin inverted
3: Arduino rx pin
4: Arduino Vin pin (is the mod duo providing 12v out on this line?)
6: Arduino rx pin inverted
7: Common Ground
shield (if present): casing (ground)
Have I understood this correctly?
Is it necessary to connect Vin? I was thinking of powering an mcu from the usb port and leave pin 4 & 5 unconnected.
Is it necessary to use inverted signals on serial pins if the distance is gonna be small? How about skippping pin 2 & 6 for a 20 cm cable?
Is the mod duo expecting serial communication with 5 volts signal voltage? Will it work with a 3.3V mcu?
Thankful for any answer! If I have totally misunderstood something, please correct me.