Hi Lefty/Mike
Your help has been really useful.
i am aware from having worked offshore for the last ten years that what i wanted is possible i just needed pointed in the right direction.
i think its peoples lazy description of the communication protocol which has confused me.
we use RS485 links to talk to an array of underwater instruments such as dopler, sonar, altimeter, bathy, profilers etc, many of which are on a RS485 bus called arcnet, believe it or not they all pass data back at very high speeds. Eg, a sonar would be useless if it couldnt return a message showing its signal its returns. The general description is to call it RS485 instead of actually saying what communication protocol it is using.
*second serial port.
i tried to describe my intention to use both a hardware and software serial link in the master so that i could communicate via a PC to the BUS, i appolegise for any confusion. I have come to the conclusion im really crap at asking questions, the guys on the forum seem to have dificulty understanding mine.
I do appreciate you are all unpaid for your assistance on the forum and have a life.
I have taken a look at modbus and over the next week or so will have a go at getting it to work for my simple Arduino programable logic controller.
I want to use RS485 because i want communication with devices over a 100m distance.