In this chapter, we will see how is the communication protocol Ethernet and how it works in general and with our equipment, taking into account the Arduino IDE perspective. We have to remember that any shield with Ethernet port can be programmed using this protocol, in our devices we have a lot with Ethernet connection like the M-Duino family and many others.
First of all, it is very important to explain the OSI model to understand all the elements which conforms a telecommunication system. The OSI is the Open Systems Interconnection model, and this is a conceptual model that characterizes and standardizes the communication functions of a telecommunication or computing system without regard to its underlying internal structure. Its main goal is the interoperability of diverse communication systems with standard communication protocols. This model is divided into seven different abstraction layers.
Every layer serves the layer above it, and it is served by the layer below it. For instance, a layer that provides error-free communications across a network provides the path required by applications above it, while it calls the next lower layer to send and receive packets that constitute the contents of that path.
The different layers are:
Application Layer: is the closest to the user, which means both this and the user interact directly with the software application.
Presentation Layer: establishes context between application-layer entities.
Session Layer: controls the connections between computers.
Transport Layer: provides the functional and procedural means of transferring variable-length data sequences from a source to a destination host, while maintaining the quality of service functions.
Network Layer: provides the functional and procedural means of transferring packets from one node to another connected in different networks.
Data Link Layer: provides node-to-node data transfer, a link between two directly connected nodes.
Physical Layer: is responsible for the transmission and reception of unstructured raw data between a device and a physical transmission medium.
Here, we can see a schematic of the layers :
It is important to keep in mind that there are two types of Modbus; the Modbus TCP that uses Ethernet and is located in layer 7, and the Modbus 232/485, which uses these protocols and is located in all the layers. We have to consider that, many times, the Network, Data and Physical layers are encompassed as media layers and the others as the host layers.
Now that we are located, we can proceed to the main explication of the video and, if you want to discover more information related to Ethernet, you can check the links than below.
Material to do practices
Arduino Leonardo or Arduino Mega (You also can use an Arduino UNO if you get it).
(The devices used with the Arduino Mega and Arduino Leonardo assembled inside have been: From the Ethernet PLCs; the M-Duino 21. From the 20I/Os PLC; The Ardbox Relay).
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