Inovance MD500-EM1 - Modbus-TCP Communication Protocol; Overview; Communication Data Frame Format

Modbus‑TCP Communication Protocol
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3 Modbus-TCP Communication Protocol
3.1 Overview
Through the built‑in Ethernet interface, the MD500‑EM1 enables the AC drive to
connect to a PC‑ or PLC‑controlled network as a slave. The network includes one
master and multiple slaves. You can carry out centralized control by using a PC or
PLC. Through the Communication protocol, you can also set the running commands,
modify or read parameters, and read the operating status and fault information of the
AC drive.
The MD500‑EM1 card supports Modbus‑TCP communication protocol. This protocol
defines the content and format of transmitted messages. If an error occurs when the
slave receives a message, or the slave cannot complete the action required by the
master, the slave responds with a fault message to the master.
3.2 Communication Data Frame Format
The following figure shows the communication data format according to Modbus‑TCP
protocol. The AC drive only supports reading or writing word type parameters. The
read command is 0x03, the write command is 0x06, and the multi‑write command is
0x10.
Figure 3‑1 Modbus request/response over TCP/IP
The MBAP header contains the following fields.
Field Length
Description
Client
Server
Transaction
identifier
2 bytes Identifier of a
Modbus
request/
response
transactions
Initialized by the
client
Recopied by the
server from the
received request
Protocol
identifier
2 bytes 0 = Modbus
protocol
Initiated by the
client
Recopied by the
server from the
received request