Mitsubishi Electric FR-E700 Series Instruction Manual page 404

Communication operation and setting
Outline
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 ded-
icated 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 as-
signed holding register address, the master can communicate with the inverter which is a slave.
NOTE 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 two hexadecimal coded characters are transmitted in one byte (8 bit) data. Only
the communication protocol is defined by the Modbus protocol, and the physical layer is not stip-
ulated.
Broadcast communication
Fig. 6-129: Message format
The data check time related to different functions is shown in the table below:
Item
Various monitors, operation command, frequency setting (RAM)
Parameter read/write, frequency setting (E²PROM)
Parameter clear/all clear
Reset command
Tab. 6-85: Data check time
● Query
The master sends a message to the slave (= inverter) at the specified address.
● Normal Response
Response after receiving the query from the master, the slave executes the requested function
and returns the corresponding normal response to the master.
● 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.
● Broadcast
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.
NOTE
The inverter executes the function independently of the inverter station number setting (Pr. 117)
during broadcast communication.
6 - 260
Query communication
PLC (Master)
Inverter
(slave)
PLC (Master)
Inverter
(slave)
Query Message
Data absence time
(3.5 bytes or more)
Query Message
Inverter response time
(Refer to the following table for the data check
time)
Response Message
No Response
Check Time
< 20ms
< 50ms
< 5s
—
Parameter
I001227E