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Communication operation and setting
4.19.7
Modbus-RTU communication specifications
(Pr. 331, Pr. 332, Pr. 334, Pr. 343, Pr. 502, Pr. 539, Pr. 549, Pr.779)
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 *
Specifies 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 ⎯
Displays the number of communication errors during
Modbus-RTU communication. Reading only
502
Stop mode selection
at communication
error
0
At Fault
Occurrence
Indication Fault Output
At Fault
Removal
0
Coasts to
stop.
E.SER Output
Stop
(E.SER)
1
Decelerates
to stop
After stop
E.SER
Output after
stop
Stop
(E.SER)
2
Decelerates
to stop
After stop
E.SER
Without
output
Automatic
restart
functions
3
Continues
running at
Pr.779
⎯
Without
output
Operates in
normal
condition
539
Modbus-RTU
communication check
time interval
9999
0
Modbus-RTU communication is available, 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 1
0 Mitsubishi inverter (computer link) protocol
1 Modbus-RTU protocol
2 BACnet MS/TP protocol
779
Operation frequency
during
communication error
9999
0 to 400Hz
Motor runs at the specified frequency at a communication
error.
9999
Motor runs at the frequency used before the communication
error.
The above parameters can be set when Pr. 160 User group read selection = "0". (Refer to page 190)
... Specifications differ according to the date assembled. Refer to page 400 to check the SERIAL number.
* The inverter works with the initial parameter setting if a value other than the setting range is set.
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.
Some functions are invalid for broadcast communication. (Refer to page 235.)
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 204)