You can use the Struct function to map data from mixed locations to a vector and from a vector to mixed locations. This is commonly used with expansion IO.
I am using a V1040 for this project. I need to have 6 buttons that act like a group of radio buttons, i.e. each button is mutually exclusive. Only one button can be active at a time and selecting a different button toggles the others off.
I use Modbus Master ActiveX Control and Delphi XE. You can also use the control with VB or VBA. With Modbus Master it is a simple matter and it is free to try. http://www.modbustools.com/download.asp
Good Luck.
Roger