The Modbus protocol is the communication protocol developed by Modicon for PLC.
The Modbus protocol performs serial communication between the master and slave using the dedicated message
frame. The dedicated message frame has the functions that can perform data read and write. Using the functions,
you can read and write the parameter values from the inverter, write the input command of the inverter, and check
the operating status. In this product, the inverter data are classified in the holding register area (register addresses
40001 to 49999). By accessing the assigned holding register address, the master can communicate with the inverter
which is a slave.
There are two different serial transmission modes: ASCII (American Standard Code for Information Interchange) mode and RTU
(Remote Terminal Unit) mode. This product supports only the RTU mode in which 1-byte (8-bit) data is transmitted as-is.
Only the communication protocol is defined by the Modbus protocol, and the physical layer is not stipulated.
(3) Message format
Data check time
Various monitors, operation command,
frequency setting (RAM)
Parameter read/write, frequency
Parameter clear/all clear
The master sends a message to the slave (= inverter) at the specified address.
2) Normal Response
After receiving the query from the master, the slave executes the requested function and returns the corresponding
normal response to the master.
3) Error Response
If an invalid function code, address or data is received, the slave returns it to the master.
When a response description is returned, the error code indicating that the request from the master cannot be
executed is added.
No response is returned for the hardware-detected error, frame error and CRC check error.
By specifying address 0, the master can send a message to all slaves. All slaves that received the message from the
master execute the requested function. In this communication, the slaves do not return a response to the master.
The slave executes the function independently of the inverter station number setting (Pr. 331) during broadcast communication.
Data absence time
(3.5 bytes or more)
Communication operation and setting
Inverter response time
(Refer to the following table for the
data check time)