Inovance MD520 Series - Transmission Mode; Data Frame Structure

Modbus Communication
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3.3 Transmission Mode
The RS485 communication network adopts the asynchronous serial half‑duplex
transmission mode. Data is transmitted frame by frame in the form of packets agreed
in the Modbus RTU protocol. An interval that is longer than the transmission time of
3.5 bytes on the communication data line marks the start of a new communication
frame.
With built‑in Modbus RTU slave communication protocol, the AC drive can respond to
the query command from the master or act according to the query command and
respond to communication data.
The master can be a personal computer (PC), an industrial control device, or a
programmable logic controller (PLC). It can communicate with a slave separately, or
send broadcast messages to all slaves. When the master sends a query command to a
single slave, the slave is required to return a response frame. For a broadcast
message sent by the master, no response from the slaves is required.
3.4 Data Frame Structure
The following figure shows the communication data format of the Modbus RTU
protocol. The AC drive allows read‑write operations on only word‑type parameters.
The communication read command is 0x03, the write command is 0x06, and the
multi‑write command is 0x10. Read‑write operations on bytes or bits are not allowed.
In theory, the host controller can read a maximum of 12 consecutive parameters.
However, it cannot read parameters across parameter groups. Otherwise, a response
error will occur.