The purpose of this technical note is to explain how the Allen Bradley 1761-NET-ENI can be interfaced with the VIM to provide a redundant network path to Allen Bradley PLCs using DF1.
The 1761-NET-ENI is an Ethernet to RS-232 gateway and isolator. Generally speaking, this is a special-case configuration and is a form of Single Chassis Redundancy. The purpose of this configuration is to eliminate a single point of failure in only the network between DeltaV and the Allen Bradley PLC CPU. This is a special-case configuration because:
This configuration is recommended when faced with the following conditions:
This configuration is compatible with ControlLogix, CompactLogix, FlexLogix, MicroLogix, and SLC5/05 controllers. The NET-ENI can be used to communicate to the serial port of the SLC5/03 and SLC5/04 PLCs but cannot be used for redundancy with VIMs. VIM firmware IOD-4102 v3.6.3 or later is required.
The Network Architecture drawing illustrates how network redundancy is achieved using the 1761-NET-ENI. In each case, the PLC is connected to the Primary PLC Network switch using an Ethernet Port. The following table explains which channels are used to establish this communication.
|Allen Bradley PLC||Ethernet Module||Channel|
|ControlLogix||1756-ENBT or 1756-EN2T||0|
Each 1761-NET-ENI will connect to the Secondary PLC Network switch via Ethernet and will connect to the respective PLC via RS-232. Each CPU has an On-board RS-232 DF1 port (Channel 0) for communication. The 1761-NET-ENI is serially connected to this port.
The 1761-NET-ENI must be configured before use. The NET-ENI can be configured using the ENI/ENIW Utility provided by Allen Bradley found here. This document discusses the configuration over RS-232. There are other methods for configuring the NET-ENI that are discussed in detail in Chapter 4 of the 1761-NET-ENI user manual.
The ENI Utility requires an RS-232 serial connection between the computer and the 1761-NET-ENI. The Allen-Bradley 1761-CBL-PM02 cable can be used to achieve this connection. Follow these steps to prepare the local serial port for communications with the NET-ENI:
Next, use the ENI Utility to modify the NET-ENI IP address and baud settings and save to the NET-ENI.
After following these procedures, the ENI will be ready for communication over Ethernet and the serial port will automatically configure the baud settings depending on how the settings are configured on the PLC serial port. The next step is to use RSLinx to locate the ENI and PLC on the network.
The serial port of the PLC must be correctly configured before serial communications can be established to the 1761-NET-ENI. The NET-ENI has the ability to automatically detect the Baud Settings as described in the configuration procedure but the Error Detection is hardcoded to CRC. This is a serial setting that needs to match in the PLC. These are the recommended settings for PLS serial ports when using the NET-ENI for VIM to PLC communications.
At this point, the 1761-NET-ENI and PLC should be able to communicate through a serial connection. The next step is to make the NET-ENI and PLC available in RSLinx.
The RSLinx setup procedure will be different depending on the PLC in question because older PLCs communicate via Ethernet while newer PLCs communicate via Ethernet/IP. See Table 2 to determine which procedure to follow for recognizing the PLC in RSLinx.
|PLC||Supported Communication Driver|
This procedure will walk through adding a SLC5/05 to RSLinx using a 1761-NET-ENI.
The driver should appear in the RSLinx driver tree and the PLC should appear under the driver as shown below. When using the Ethernet driver, the NET-ENI will not be viewable; the PLC will simply appear to have the IP Address of the NET-ENI. The PLC will be ready to use for RSLogix and/or VIM communication once the PLC appears under the driver in RSLinx.
Note: The NET-ENI will actually appear under the Ethernet/IP Driver tree as well, but reaching Ethernet IP devices through that driver will not be possible.
This procedure will walk through adding a FlexLogix PLC to RSLinx using a 1761-NET-ENI.
The EtherNet/IP driver should appear in the RSLinx driver tree and the NET-ENI will appear under the driver as shown below. The PLC will be nested under the NET-ENI. At this point the PLC will be ready for using for RSLogix and VIM communication.
At this point, the 1761-NET-ENI and PLC should have valid serial communications and should be reachable through RSLogix via RSLinx. The next step is to add the NET-ENI to the VIMNet Explorer configuration.
The next step in the process is to add the redundant PLC to the VIMNet Explorer Configuration. This process configures the VIMs to establish communication to the primary PLC interface and the 1761-NET-ENI.
At this point, the VIMs are configured to communicate to the PLC via the primary interface and to the secondary interface via the 1761-NET-ENI. The final step is to configure DeltaV to read and write to the PLC.
This process will walk through adding the redundant VIMs, the redundant PLC, and using the Special Data to communicate to the 1761-NET-ENI.
|PLC||Special Data 4||Special Data 5|
After following all of the steps up to this point, the VIMs should be communicating redundantly to the PLC using the 1761-NET-ENI.
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