Mitsubishi Electric FR-A700 Instruction Manual page 649

Parameter
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
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..
NOTE There are two different serial transmission modes: ASCII (American Standard Code for
Information Interchange) mode and RTU (Remote Terminal Unit) mode. This product sup-
ports 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 stipulated.
Query communication
Broadcast communication
Fig. 6-230: 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 (EEPROM)
Parameter clear/all clear
Reset command
Tab. 6-147: Data check time
● Query
The master sends a message to the slave (= inverter) at the specified address.
● Normal
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 slave executes the function independently of the inverter station number setting
(Pr. 331) during broadcast communication.
FR-A700 EC
PLC (Master) Query Message
Inverter
(slave)
Data absence time
(3.5 bytes or more)
Query Message
PLC (Master)
Inverter
(slave)
Communication operation and setting
Inverter response time
(Refer to the following table for the data
check time)
Response Message
No Response
Check Time
< 12ms
< 30ms
< 5s
—
I001227E
6 - 469