Communication
‑696‑
Application
The AC drive is connected to a "single‑master multi‑slave" PC or PLC control network
with RS485 bus.
Hardware interface
The RS485 extension card MD38TX1 must be inserted into the AC drive.
Topology
The system consists of a single master and multiple slaves. In the network, each
communication device has a unique slave address. One of the devices (usually a PC
host controller, a PLC, or an HMI) is the master and initiates communication to
perform parameter read or write operations on slaves. Other devices (slaves) provide
data to respond to query or operations from the master. Only one device is allowed to
transmit data at a time, whereas other devices should be in data receiving status.
The address range of the slaves is 1 to 247, and 0 is a broadcast address. A slave must
have a unique address in the network.
Communication 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. According to the Modbus‑RTU protocol, an interval of at least 3.5‑byte
transmission time marks the end of the previous message. A new message starts to be
sent after this interval.
The communication protocol used by the AC drive is the Modbus‑RTU slave
communication protocol, which allows the AC drive to provide data to respond to
"query/command" from the master or execute actions according to "query/
command" from the master.
The master can be a PC, an industrial control 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 "query/command" from the master. For a broadcast message sent by
the master, the slaves need not return a response.
4.1.3 Communication Data Frame Structure
The following figure shows the Modbus‑RTU communication date. The AC drive
supports read and write of word‑type parameters only. The read command is 0x03,
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