Set Coils and Fetch Discrete may not be valid commands for the controller. I would think all the registers are integers and nothing would be boolean. Some registers might inherently be boolean, but are handled as a 0 or 1 in a holding register.
Set Holding Registers may not work with certain addresses as some are going to be read only. Only use Set for those register addresses that are read/write.
I've worked with the Control Techniques drives so I know you can do Modbus with them. I don't know if they've changed anything in the newer models of drives after Nidec bought them.
One thing to keep an eye on is the slave address or unit ID. I do remember using the purple modbus library which assumes a particular unit ID by default. But I think Control Techniques uses different unit ID's depending on whether it is the drive base, or an add on module. Like Id 0 worked for one, ID 1 worked for another, maybe even 2, 3, 4 if you have add-on modules. And also some crazy high unit ID's also worked like a ID of 253 gave me the same access to address that 1 did (I probably am remembering some of those numbers wrong.)
All I can say is thoroughly read their communications guide. The Advanced User Guide will tell you things they leave out of the Basic User Guide.
