It's connected using one of these that I actually bought for something else a while ago Jay.

USB to RS485 Adapter Dongle Converter FTDI Chipset - EPOS, CCTV, Industrial | eBay

Cable was a length of 0.5 CY cable that I had left over from wiring up the drivers. Shield wasn't run to ground at either end so will try running it to ground at computer end when I go up the unit today.

I just used bit's that I already had but if they are not suitable then I will happily go out & buy the right bits if it means it will work. The motherboard has a serial connection on it already so wouldn't be a problem to use that although it does drive my plotter at the moment.