mort81,
You would only need to use Block Transfer instructions for analog or speciality modules. For discrete I/O modules, once the I/O Configuration is successfully completed, there will be Controller Tags created for both Input and Output data, which may be directly referenced, or alias referenced from the program(s).
souviknaskar,
Do let us know if any of the distributed I/O modules are analog, etc.?
Have you done anything yet or are you just doing preparatory work before proceeding?
You should have a ControlNet Bridge module (CNB, CN2) in the local chassis with the 1756-L71 processor.
Are you saying that you have one distributed 1771-A2B 8-slot chassis with one adapter and 7 x I/O modules? (I think this is what you mean?)
Or are you saying that you have 7 x 1771 chassis' with an, as yet, undisclosed number slots and I/O modules per chassis? (I want to be sure you don't mean this?)
For "a" distributed I/O rack, you should have a 1771-ACN15 ControlNet adapter module. Under the "I/O Configuration" section, in your project for the 1756-L71, you add the 1771-ACN15 adapter module under the 1756 ControlNet bridge module and then under the properties for the ACN you assign its name and node number. The node number of the ACN is configured via its rotary switches. Here, you also assign the Input and Output data sizes for the I/O modules that are under the control of the ACN adapter.
These sizes are determined by the type of modules being used and the "slot addressing" dip switch settings for the distributed chassis. For instance, if using 16-point discrete modules and the chassis is set for 1-slot addressing, in an 8-slot chassis, then you would set both the Input and Output data sizes to 8 x 16-bit words each.
Once the I/O sizes are configured and applied, the Module-Defined Controller Tags for the discrete I/O modules will have been created. For the Input data you should see a Module-Defined tag which will contain a "RackStatus" DINT, an "InputGroupsValid" DINT and the actual Input data in a 16-bit integer array. For the Output data you should also see a Module-Defined tag with just the Output data in a 16-bit integer array.
If you are using any analog or speciality modules then it will get a bit trickier with the Block Transfer Messages. But we can cross that bridge if and when we get to it.
When you add or reconfigure devices you will have to re-schedule your ControlNet network using RSNetWorx for ControlNet. Assuming you also have this software?
I think that's enough to get you going. Any more questions just fire away.
Regards,
George