Inovance H3U Series - Page 599

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9
9 Communication9.4 Modbus Protocol
9.4 Modbus Protocol
RS-485 signals underlie Modbus communication. Twisted pairs are used for connection. Therefore, the
transmission distance is long and up to 1,000 meters. With high interference immunity and low cost, Modbus
communication is popular among industrial control devices. Many AC drive and controller manufacturers use
Modbus protocols.
Data is transmitted in hexadecimal (HEX) and ASCII modes through Modbus-RTU and Modbus-ASC, respectively.
In hexadecimal mode, data can be directly transmitted; in ASCII mode, data must be converted into ASCII codes
rst. Therefore, communication through Modbus-RTU is more efcient, less complicated, and more popular.
Modbus communication is in "single-master multi-slave" mode, in which the master station initiates sessions and
the slave stations respond passively. Therefore, controlled devices (for example, AC drives) have slave station
protocols, while controlling devices (for example, PLCs) have master and slave station protocols.
9.4.1 Modbus Master Station Communication
Modbus-RTU and Modbus-ASC instructions can be executed on COM1.
1) Hardware connection
COM1
COM0
COM1
COM0
RS485, Modbus protocolMaster
Slave 1
COM1
COM0
Slave 254
H3u
H3u H3u
2) Software conguration