Vacon 100 INDUSTRIAL, Инструкция по установке и эксплуатации

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Modbus - general info vacon • 6
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2. M
ODBUS
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GENERAL INFO
Modbus is a communication protocol developed by Modicon systems. In simple terms, it is a
way of sending information between electronic devices. The device requesting the information
is called the Modbus Master (or the Client in Modbus TCP) and the devices supplying informa-
tion are Modbus Slaves (in Modbus TCP servers). In a standard Modbus network, there is one
Master and up to 247 Slaves, each with a unique Slave Address from 1 to 247. The Master can
also write information to the Slaves. Modbus is typically used to transmit signals from instru-
mentation and control devices back to a main controller or data gathering system.
The Modbus communication interface is built around messages. The format of these Modbus
messages is independent of the type of physical interface used. The same protocol can be used
regardless of the connection type. Because of this, Modbus gives the possibility to easily up-
grade the hardware structure of an industrial network, without the need for large changes in
the software. A device can also communicate with several Modbus nodes at once, even if they
are connected with different interface types, without the need to use a different protocol for ev-
ery connection.
Figure 1.Basic structure of Modbus frame
On simple interfaces like RS485, the Modbus messages are sent in plain form over the net-
work. In this case the network is dedicated to Modbus. When using more versatile network sys-
tems like TCP/IP over ethernet, the Modbus messages are embedded in packets with the
format necessary for the physical interface. In that case Modbus and other types of connec-
tions can co-exist at the same physical interface at the same time. Although the main Modbus
message structure is peer-to-peer, Modbus is able to function on both point-to-point and mul-
tidrop networks.
Each Modbus message has the same structure. Four basic elements are present in each mes-
sage. The sequence of these elements is the same for all messages, to make it easy to parse
the content of the Modbus message. A conversation is always started by a master in the Mod-
bus network. A Modbus master sends a message and—depending of the contents of the mes-
sage—a slave takes action and responds to it. There can be more masters in a Modbus
network. Addressing in the message header is used to define which device should respond to
a message. All other nodes on the Modbus network ignore the message if the address field
doesn't match their own address.
Your Vacon 100 HVAC drive is equipped with Modbus support as standard.
Master’s
message
Slave
response
Address
Function
Data
CRC
Address
Function
Data
CRC
Start
End
Start
End