Connect Arduino to MDB as master

Hi, I try to connect my Arduino Mega to the MDB interface as VMC master. I tried to connect it directly (RX to master receive, TX to master transmit) and with optokopplers in between, but nothing seems to work. Can anyone help me pls with this shematik? I think for the transmit side this is just a signal boost, but the arduino has already a 5V signal, so is this necessary?

|500x395

greetings Tarcontar

Hello https://github.com/perdidor/Arduino-MDB-UART