Inovance MD500T75G - Modbus Communication Protocol

8. Interfaces and Communication MD500 User Manual
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8.5 Modbus Communication Protocol
The MD500 provides the RS485 communication interface and supports the Modbus-RTU communication protocol so that the user
can implement centralized control, such as setting running commands and function codes, and reading working status and fault
information of the AC drive, by using a PC or PLC.
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broadcasting) format and master coding method (function code for the action, transmission data, and error check). The slave uses
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slave receives a message, or the slave cannot complete the action required by the master, the slave returns a fault message as a
response to the master.
8.5.1 Application
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8.5.2 Bus Structure
6. Interface mode
The RS485 extension card MD38TX1 must be inserted onto the AC drive.
7. Topological structure
The system consists of a single master and multiple slaves. In the network, each communication device has a unique slave
address. A device is the master (can be a PC, a PLC or an HMI) and initiates communication to perform parameter read or write
operations on slaves. The other devices (slaves) provide data to respond to the query or operations from the master. At the
same moment, either the master or the slave transmits data and the other can only receives data.
The address range of the slaves is 1 to 247, and 0 is the broadcast address. A slave address must be unique in the network.
8. Transmission mode
The asynchronous serial and half-duplex transmission mode is used. During asynchronous serial communication, data is sent
frame by frame in the form of message. In the Modbus-RTU protocol, an interval of at least 3.5-byte time marks the end of the
the previous message. A new message starts to be sent after this interval.
Master sending 1
Slave response 1
Interval of at
least 3.5-byte
time
Data frame
A
B
Master sending 2
Slave response 2
Data frame
Interval of at
least 3.5-byte
time
The communication protocol used by the MD500 is the Modbus-RTU slave communication protocol, which allows the MD500
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from the master.
The master can be a PC, an industrial device, or a PLC. The master can communicate with a single slave or send broadcast
messages to all slaves. When the master communicates with a single slave, the slave needs to return a message (response) to
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