1756-CDB / D module data

I think you are referring to a 1756-CNB module, series D, which is a ControlLogix ControlNet Bridge (Communications) module. There is no such module as a 1756-CDB

When you insert any module into the I/O configuration "tree" of a project, the system automatically creates the required tags to allow it to pass data into and out of the module.

Either two or three tags will be created, in the example here a module is created in slot 4 :

Local:4:O - this tag holds Output data, from the controller to the module, only required for a module that has Output data.
Local:4:I - this tag holds Input data, from the module to the controller. Input data from an output module is module and channel status and fault information.
Local:4:C - this tag hold configuration data, it is sent to the module from the controller to tell it how to work, how the channels are configured etc.


For your CNB module, no tags are created for the Local CNB (the CNB in the same chassis as the controller)...

When you add a remote CNB, however, tags will be created if, and only if, you choose the Rack Optimisation Comm format. These I and O tags contain the I and O data for digital I/O modules in the remote chassis. (Rack Optimisation makes the comms module act like a remote I/O scanner - handling discrete (digital) I/O only - Rack optimisation can reduce the number of "connections" needed, of which you have only 250 to play with).

The CNB module does not require a ...:C (configuration) tag, and it is not created.

The RJ45 connector on the front of the CNB module looks just like an Ethernet port, and an Ethernet plug fits it nicely (which you would expect since it is an RJ45), however, it is not an ethernet port, but a port for connecting a PC for programming access, via ControlNet, using a special cable, and a 1784-PCC or 1784-PCIC card in your PC. Someone will jump in with the cable part number.

Hope this helps, and feel free to ask if you need further explanation.

oh 1756-CNB,thanks

Look into the Controller Tags database.

You will find your Local:4:O and Local:4:I tags there.

You will see + sign on the left of the tag, click to expand the tag and you will see the structure of the tag.

If it is an I/O module, or a remote comms module setup for Rack Optimisation, you will ulimately find .Data elements. Here is the I/O data associated with the field devices.