using rsview object model(in vb5) i could move data to and from modbus devices(via serial port)directly to the memory tags in rsview and not through some dde or opc server, that is i did not require any devices tags. So in effect why are there device tags? or have i taken some dangerous shortcut?

 

Device tags exist because most people are not going to write their own code to interface to I/O. They will use the existing drivers, which use device tags. If you wrote and tested your interface code properly, then you have done nothing wrong, IMHO. If you have taken shortcuts, such as ignoring error handling, then you may see some problems. Bill Sturm

 

Thanks, but specifically why have two different types of tags, especially when one them has a count limit. Could not existing drivers be themselves be written to modify to the memory tags directly, more to the point that dde are awkward to write.