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Disclaimer: This document is written in the hope that you can utilize for your own education to gain knowledge of PLC systems (should you decide to utilize this document). Although I believe the information in this document to be accurate, it is YOUR responsibility to verify this information before implementing it in any way, especially when damage to personnel or equipment could result. By continuing to read this document, you agree to hold no one who writes, modifies, or distributes this document liable in any way (even negligence). Due to the wide variety of plant applications, some of the examples in this document may be prohibited at your location, or could cause damage to equipment, or harm personnel.

Author: Ricky Bryce (Montgomery County, IL)

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Remote Chassis

In many systems, many points of I/O are located far away from the local chassis. The local chassis is the chassis where the processor in focus resides. In many cases, it is easier to mount a chassis at the remote location. A communication cable will allow the processor to control the chassis at the remote location. For example, if 256 points of I/O were 300 feet from the local chassis, it would be easier to mount a chassis at the remote location. You would then run the 256 points of I/O just a few feet to the remote chassis, then run one communication cable back to the local chassis.

The example below shows the Ethernet/IP communication protocol, however, many other protocols follow the same model such as ControlNet or Remote I/O with slightly different wiring and configuration changes.

Look at the diagram below. In this example, we have an input and output module in the local chassis. This would be for I/O in the local vicinity. For I/O in another location, we can use a remote chassis. The processor will establish a connection to this remote I/O, and will read inputs, and control outputs on this chassis. In this example, the local chassis is ControlLogix, and the remote chassis is FLEX I/O (This could also be many other types of chassis such as another ControlLogix chassis, PLC-5 Chassis, SLC Chassis, Block I/O, etc....). This procedure will assume that you have an existing program, and that IP addresses have already been assigned to the Ethernet module, and Ethernet Adapter. If you were to use ControlNet, you would assign node numbers instead of IP addresses. You can assign node numbers to thes modules by physically dialing in a node number on the modules themselves. For Remote I/O, you would set up the DIP switches according to the user manuals for each module.

Communication path

Look at the diagram below showing the communication path. The processor is where the program resides, so the path we choose will be relative to the processor itself.

The processor must first connect to the 1756-ENBT module in the local chassis. If you are using ControlNet, this would be a 1756-CNB(R) module. For the older remote I/O Protocol, this would be a 1756-DHRIO module.
Next, we must tell the local 1756-ENBT module to connect to the adapter at the remote chassis. Remember we are using Flex I/O for this particular example, so we would connect to the 1794-AENT module (ethernet) 1794-ACN(R)(ControlNet), or 1794-ASB (Remote I/O).
The next step is to have the adapter connect to the individual modules within it's chassis. We are using the following modules:
1. Slot 0 – 1794-IB16 (DC input module)
2. Slot 1 – 1794-OB16 (DC output module)
3. Slot 2 – 1794-IE8 (Analog input module)

I/O Configuration

Now that we have decided the layout for our system, we need to go to the ControlLogix project, and set up the remote chassis under I/O Configuration. Recall that 3 steps will accomplish this connection: First, we connect to the Local ENBT module, then the ENBT will connect to the AENT. Next, the AENT will connect to the modules that are in it's own chassis.

If you do not already have the Ethernet module set up in your I/O Configuration, right click the I/O Configuration folder, and select 'New Module'.
Select the 1756-ENBT module from the list of available modules, then press OK.
Next, you will choose the major revision of the 1756-ENBT module. This revision is usually on the label on the side of the module, however, this label may not be up to date. You can use the module information from RSLinx, or type the IP address into your web browser, and click 'Module Information' to determine the revision level. At the time this manual was written, the modules we use for class are 2.4. This means the Major revision is 2, and the minor revision is 4. Therefore, we must select 2 as the major revision. Press OK when finished.
Next, complete the dialog box for the Ethernet module. Your location may have specific naming standards, but we will name this module 'Local_Ethernet_Module'. The IP address scrolls across the front of the ENBT module (assuming an IP address has been assigned). In our classroom, the ENBT module is in slot 3, and the minor revision is 4 (Recall the module's revision was 2.4, 2 being the major, and 4 being the minor). We will leave the keying as compatible module. Press FINISH.
Our next step is to have the 1756-ENBT connect to the 1794-AENT module. In I/O Configuration, right click on the ENBT module. Remember we are connecting to the AENT module from the ENBT module (Not directly from the backplane)
Choose the 1794-AENT from the list of available devices. Press OK. (Be sure you select the 1794-AENT
Next, select the major revision of the AENT module. We can get this information from the web browser, by typing the IP address into the browser's address bar, and click 'Module Configuration'. At the time this manual was written, the AENT module had firmware version 2.12. Therefore, we must enter 2 as the major revision.
You may have naming conventions for remote chassis at your own location. For our classroom use, we will name the module 'Remote_Chassis'. You can usually get the IP address of this module from your network administrator, schematics, or other documentation if the address was not written on the front of the module. Use the IP address the instructor assigns to you. We will leave the comm format as 'Rack Optimization', and this will treat the three modules in the chassis as a single connection instead of having a separate connection for each module. The 1756-ENBT module only supports 64 connections in many cases. This chassis consists of 3 slots (not counting the adapter). The minor revision is 12 (because our version was 2.12), and leave the keying as 'Compatible Module'. Press FINISH when you are finished configuring the module.
Now that a connection has been made between the ENBT module and the AENT module, we need to establish a connection between the AENT module and the three modules that are in it's chassis. To add the first module (The 1794-IB16), right click the AENT module in the I/O Configuration, and select 'New Module'.
Choose the 1794-IB16 module from the list of available modules, then press OK.
Complete the Module configuration dialog as follows, then press FINISH.
Next, we will add the 1794-OB16 module to the I/O Configuration tree. Again, we are connecting to this module from the 1794-AENT module, so right click the AENT module, and select 'New Module'
From the list of available modules, select the 1794-OB16 DC output module. Press OK.
Complete the module configuration dialog as shown, then press FINISH.
Next we need to add the last module to the remote chassis. This will be the 1794-IE8. This connection will be between the AENT and the IE8 module (Just like the AENT connected to the previous two modules we configured. Right click the 1794-AENT module, and select 'New Module'.
From the list of available modules, choose the 1794-IE8 module, then press OK.
Comlete the module configuration dialog as shown, then press FINISH.
Now that all of our modules have been added to the I/O Configuration, RSLogix has created tags for us in the controller tag database. Let's take a look at the controller tags to see where data from these three modules will appear.
Take a look at the tag names that RSLogix generated for us.
Notice the tag names assume the name of the adapter in the remote chassis. You will also notice for this example, that we have two tags for each slot. The slot number immediately follows the tag name.

Since we extablished a connection to each module in the chassis individually, we have two sets of tags for this remote I/O. We have the base tags, which contain most all of the information we need to know about the chassis, and we have the derived tags which follow the same naming convention as the local I/O. The derived tags alias corresponding memory locations in the base tag that reflect the data for it's own slot when possible.

If you go to edit tags, you will see what based tags the derived tags are aliasing.

For this course we will be using the derived tags. To see the data from the DC Input Module, you must be online, on the monitor tags tab, then expand Remote_Chassis:0:I. You will see each input from this module. These tags can be used directly in ladder logic, or you can create another alias to use for your project.