Acquire Data Using An Easy Communication Standard

Modbus refers to a standard of communication which has been in use since the late seventies. The company Modicon was the first one to establish the Modbus interface of communication. This interface exists in between the client and the server. When a client wishes to obtain information from the server, Modbus serves the purpose.

Interface Between Client And Server

The protocol of data acquisition using Modbus is as follows. First the client requests his required data from the server. He can also order the server itself to carry out a particular function. Whichever case it is, the work in question is referred to by a function code. That is when the client wishes a particular function to be performed he can use the corresponding function code so that the server understands the need of the client. When the client gives the function code followed by the address of the data, the server locates it and does whatever function is required on that data.

Protocol Data Unit And Application Data Unit

These messages that get exchanged between the client and the server are referred to as the frames. Such frames come under two categories, Protocol Data Unit known as PDU and Application Data Unit known as ADU. PDU usually includes a function code and the data in question. ADU also includes the same, but with an additional error checking function. The address of the data being transacted between the client and server during data acquisition is also included in ADU. This address information is used by the server to locate the data.

Discrete Input, Input Registers, Coils And Holding Register

The data involved in a Modbus protocol can be classified into four types. The first type is called discrete input. This input is of Boolean type and is read-only in nature. That is, the clients can only read this kind of input and make no changes to it. The second type is called input register which is also read-only in nature like the previous type with the only difference that it is a 16-bit type of input. The third type of data is called coils which are both read and write in nature. That is, the client can work on this data and make modifications to it. The fourth type is called holding register which works the same way as coils. While the coils are of one-byte type, holding registers belong to 16-bit category.

Hey myself Archer Finch. Even though I took extra care about my systems, but still it was more prone to hacking. With the introduction of the Modbus systems, my system is now very much safe from all sorts of threats, as most of the data acquisition systems are connected to web based portals or products.

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