Mick
Yes, the GND pins you mention above are what we are talking about. Essentially, we are saying that this ground potential must also be the one used by the drive as a reference for its ESM outputs.
I haven't had time to give the manual much attention as yet but it looks as if pin 49 on CN1 is the only common ground for all of the drive's digital signals. It is also the common for the 24V power supply to the drive. As we don't want to contaminate any of the analogue grounds with digital noise, pin 49 appears to be the only option.
Assuming you are using the same 24V supply for the drives and for CSMIO, their commons are bound to be connected, and that, in essense, should be enough. If you have separate 24V supplies, make sure that their 0V commons are connected together. If the cable you are using has a ground wire, by all means connect it to one of the CSMIO ground pins. If it only contains the 6 ESM signals, just make sure the power supply ground is common for the CSMIO and the drives as above. It is unlikely that you will experience noise issues on these differential signals, and unless you do, I wouldn’t worry about it any further.
Allan
P.S. I somewhat sloppily tend to use the workds ground and common interchangeably. To be clear, in both cases I am referring to the circuit 0V line, and not to the protective earth (though these will likely be bonded somewhere).