Routing Paths

Ethernet/IP (CIP) Routing Paths

NOTE : As of version 3.99r only Ethernet card routing is available

The CIP protocol is designed to allow routing through complex networks. For example, you may have a ControlLogix rack with multiple Ethernet cards acting only as a gateway. If you HMI is connected to one Ethernet card and a PLC attached to the other Ethernet card, the RoutePath will tell the driver how to find the PLC.

Routes are designated by pairs of numbers, the port and the link address. The port can be thought of as a doorway on a device. For example, the 1756-EN2T card has 2 communication ports (or doorways) for communication packets to pass through. The connector to the backplane is considered port 1 and the front Ethernet port is considered port 2.

Let's consider the example of a ControlLogix rack with (2) 1756-EN2T cards. The first is in slot 1 with the HMI connected to it. The second is in slot 2 with a PLC connected at IP address 192.168.1.10

To build the appropriate route path..... Since our HMI is connected to the card in slot 1, the communication packets go directly into that EN2T card. We now need the packet to exit the card (out the back door if you may) and go onto the backplane. Once on the backplane, we want the packet to then enter the card in slot 2. Once inside the EN2T in slot 2, we want the packet to exit the Ethernet port (front door) to get to the PLC. The front port/Ethernet port on an EN2T is designated at port 2. The final destination is address 192.168.1.10, so our final RoutePath would be this:

1,2,2,192.168.1.10

This can be viewed as needing to pass through 2 devices (two EN2T cards). As mentioned above, each route segment requires a pair of values. So think of them as x,y. We can designate the pair for segment 1 as X1,Y1. And the pair for segment 2 as X2,Y2. With that, the route path can be broken down as such:

X1 = 1 Port 1 of the first EN2T Y1 = 2 Port 2 (backplane) of the first EN2T X2 = 2 Slot 2 of the backplane Y2 = 192.168.1.10 The link address (IP Address of the PLC) after leaving the second EN2T

A key element is to know the port number designation for each device. The EN2T card only has 2 ports, the backplane port designated at port 1 and the Ethernet port designated as port 2. Other devices/cards may have more than 2 ports.

These are some common known port numbers for various devices:

1. The backplane
2. Depends on the module this number is used on:

• DH-485 - out channel A
• DHRIO - out channel A
• DNB - out onto DeviceNet
• CN2,CNB(R) - out onto ControlNet
• EN2T,Ethernet,ENBT - out onto EtherNet
• Controllers - out the serial port

3. Depends on the module this number is used on:

◦ DH-485 - out channel B
◦ DHRIO - out channel B

The second value in the pair is the link address. These are some common address for various devices:

• ControlNet - ControlNet Node Address (0-99)
• Ethernet - Ethernet IP address (a.b.c.d)
• RS-232 Serial port - DF1 node address (0-255, use 1 for a point-to-point connection)
• The backplane - Backplane slot number (0-16, depending on chassis size)
• Data Highway Plus - Decimal equivalent of the Octal Data Highway Plus node address or (8#10) means that the number 10 is in octal. (0-63 decimal or 8#00 to 8#77)

Another Technique

If this is still sounding confusing and you are not sure you have the correct route path, here is a technique that can help make it easier.

- Using RSLogix5000, add all of your devices to the IO Tree
- Add an MSG instruction to the ladder logic
- Go into the MSG configuration where you set the Path
- Use the Browse to select the target device from the tree you created
- Now remove the devices from the tree and go back to the MSG configuration
- RSLogix should have translated the Path into a "raw" format