That makes it sound easier than I thought...im googling.
Thanks Ecosse
The device at the end of the cable should be the slave.
If you unplug from the power cable end of the device at the end, you'll see a diagram and four (normally) little jumpers,
It'll tell you which way to to place the jumpers depending which mode you wish to make the device act as.
One must be the master and one must be the slave. convention is to make the one at the end of the cable the slave.
Dougie.