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Communication operation and setting
4
4.24.6 Modbus-RTU communication specifications (Pr. 331, Pr. 332, Pr. 334, Pr. 343, 
Pr. 539, Pr. 549)
(1) Communication specifications
⋅ The communication specifications are given below.
Using the Modbus-RTU communication protocol, communication operation or parameter setting can be
performed from the RS-485 terminals of the inverter.
Parameter 
Number
Name
Initial Value
Setting Range
Description
331
RS-485 communication station 
number
0
0
Broadcast communication is selected.
1 to 247
Specify the inverter station number.
Set the inverter station numbers when two 
or more inverters are connected to one 
personal computer.
332
RS-485 communication speed
96
3, 6, 12, 24, 48, 
96, 192, 384
Set the communication speed.
The setting value 
× 100 equals the 
communication speed.
For example, the communication speed is 
9600bps when the setting value is "96".
334
RS-485 communication parity 
check selection
2
0
Without parity check
Stop bit length 2bits
1
With odd parity check
Stop bit length 1bit
2
With even parity check
Stop bit length 1bit
343
Communication error count
0
Display the number of communication 
errors during Modbus-RTU 
communication. Reading only
539
Modbus-RTU communication 
check time interval
9999
0
Modbus-RTU communication can be 
made, but the inverter trips in the NET 
operation mode.
0.1 to 999.8s
Set the interval of communication check time.
(same specifications as Pr. 122)
9999
No communication check (signal loss 
detection)
549
Protocol selection
0
0
Mitsubishi inverter (computer link) 
protocol
1
Modbus-RTU protocol
CAUTION
When Modbus-RTU communication is performed from the master with address 0 (station 0) set, broadcast communication is
selected and the inverter does not send a response message to the master.
When response from the inverter is necessary, set a value other than "0" in Pr. 331 (initial value 0).
Some functions are invalid for broadcast communication. (Refer to page 349)
REMARKS
⋅ When using the Modbus-RTU protocol, set Pr. 549 Protocol selection to "1".
⋅ When the communication option is fitted with Pr. 550 NET mode operation command source selection set to "9999" (initial value), the
command source (e.g. run command) from the RS-485 terminals is invalid. (Refer to page 322)
Item
Description
Related 
Parameters
Communication protocol
Modbus-RTU protocol
Pr. 549
Conforming standard
EIA-485 (RS-485)
Number of inverters connected
1: N (maximum 32 units), setting is 0 to 247 stations
Pr. 331
Communication speed
Selected among 300/600/1200/2400/4800/9600/19200/38400bps
Pr. 332
Control protocol
Asynchronous system
Communication method
Half-duplex system
Communication 
specifications
Character system
Binary(fixed to 8 bits)
Start bit
1bit
Stop bit length
Select from the following three types
⋅ No parity, stop bit length 2 bits
⋅ Odd parity, stop bit length 1 bit
⋅ Even parity, stop bit length 1 bit
Pr. 334
Parity check
Error check
CRC code check
Terminator
Not used
Waiting time setting
Not used