Hi Robin2 and dougp,
I have told you from my point of view how this stuff works something is getting lost in translation, the victron software via the usb to serial dongles that you connect to your devices will sens what is plugged in and the Victron software will display what devices are connected to the laptop you can then choose which devices Data you would like to view, you can however ONLY view one device at a time within the Victron software, each device needs its own usb to serial dongle the dongles convert to a UART connector that connects to each device, I am able to replicate the usb to serial dongle with the Arduino and to view the Data , I would have liked to have been able to have the Arduino "switch" between the two devices via a bit of code so that the Victron software can sens one or the other device via a switched state through the Arduino. I have reverted back to my first bit of code and put in a DPDT switch, I wired the two devices RX/TX wires to either side of the switch and the center contacts to the RX/TX pins of the Arduino and I am via that able to switch to either one or the other device to view its data, I would have liked the Arduino to have also been the switch as well as the dongle.
Thanks for all your help but it seems that I am asking the impossible for the Arduino.
Kind regards.
Charles.