Application Notes

EAP-032043

Ethernet - you still need to specify the protocol

Communications with today's industrial equipment is saturating with the word Ethernet. Articles on Ethernet seem written toward the software programmer versus the guys in the field trying to sell Ethernet. M-System is releasing the R5 Ethernet module model R5-NE1. I thought I would try and help with understanding Ethernet for the sales person.

The two most common statements I hear is, "We are installing Ethernet" or "I need an Ethernet device". This basically tells me the electrical interface but does not tell me what protocol that is needed. Due to the exposure to the office Ethernet, we think you just plug it in and it works. We still need a driver to get our printers to work and Ethernet industrial equipment is the same way. Another example is saying we need an RS485 device without adding that you need it to be Modbus RTU versus proprietary protocol. Ethernet has one key advantage that most networks do not, support for the co-existence of multiple protocols simultaneously. This is one key item that makes Ethernet so attractive.

How does "Ethernet" support multiple protocols simultaneously? A common term associated with Ethernet is TCP/IP. TCP stands for Transport Control Protocol. This might be easier to remember as Traffic Cop Protocol, telling data where to go on an Ethernet network. IP stands for Internet Protocol (the traffic cop for the internet). Do we care about these details as sales people? Not really except, the IP indicates the unit is capable of being addressed from the Internet Without IP, the unit is restricted to the internal network of the facility.

TCP/IP protocol surrounds an existing protocol such as Modbus RTU, allowing multiple protocols to co-exist on the same network. It is very analogous to the wrapping paper on a Xmas present. You don't know what's inside or being sent, until you remove the wrapping. Who does the wrapping and who does the unwrapping? In this case, M-System Model R5-NE1 is doing the wrapping. It will send a Modbus RTU protocol wrapped around with TCP/IP protocol and place the data packet onto an Ethernet network.

The Control Room is setup to receive information packets in a Modbus TCP/IP format. Eager and excited, the control computer strips off the TCP/IP wrapping and then deciphers the standard Modbus RTU information. The control computer, after careful inspection of the data packet, will either rejoice or get through a tantrum and set off alarms.

The control computer could be setup to accept Profibus, DeviceNet, Fieldbus or some other protocol as well on the same Ethernet connection. The requirement is that the protocols must also use the same wrapping paper, TCP/IP in this case. The computer must remove the TCP/IP wrapping each time it receives a data packet to see what's inside.

In closing, when you do run across an Ethernet application, don't forget to ask what communication protocol they intend to use or are using. Not mentioned before, but verifying network speed, 10Mbps or 100Mbps, is another key parameter. It will save you a phone call later.

M-System has flexible solutions to meet your specific application and requirements. Consult our Signal Conditioners Data Library.