Types of Ethernet/IP communication

Types of Ethernet/IP communication

Implicit Communication:

Periodic communication between an Adapter and a Scanner, often referred to as cyclic communication, is employed to facilitate the regular exchange of real-time data between the Scanner and the Adapter. This form of communication is essential for the timely exchange of time-sensitive data.

Cyclic communication is primarily utilized for input-output (IO) data transfer and is commonly employed to exchange information between a Programmable Logic Controller (PLC) and a variety of devices.

For instance, let’s consider a scenario where a Rockwell PLC functions as the Scanner, and a Variable Frequency Drive (VFD) acts as the Adapter. In this context, parameters such as the VFD’s frequency and start/stop commands are typically encompassed within Implicit communication. Due to their time-critical nature and their importance for the VFD’s proper operation, these parameters are transmitted using methods optimized for real-time performance.

In the context of this example, data transmission occurs using the User Datagram Protocol (UDP) as the chosen transport protocol method.

As illustrated in the image below, parameters like frequency are categorized under Implicit communication, owing to their substantial significance for the functioning of Variable Frequency Drives (VFDs).

Explicit Message Communication:

This mode of communication is employed for transferring data that is less time critical. It follows a request and reply to paradigm, where the client initiates communication by sending a request. The server then processes this request and subsequently sends a response. Also known as Acyclic communication, this method relies on event-based communication. It is primarily utilized for exchanging information between two PLCs and for reading and writing data from devices not covered by implicit message communication. This type of communication utilizes the TCP method as the transport protocol.

Example1-

Example2.

VFD parameters such as DC Bus Voltage are included in Explicit message communication due to their non-critical nature. In this setup, the Programmable Logic Controller (PLC) requests data from the VFD only when it needs to read these parameters.

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