Mitsubishi Electric FR-F720P-0.75K to 110K Instruction Manual page 271

Communication operation and setting
(9) Signal loss detection (Pr. 539 Modbus-RTU communication check time interval)
If a signal loss (communication stop) is detected between the inverter and master as a result of a signal loss
detection, a communication error (E.SER) occurs and the inverter output is shut off.
· When the setting is "9999", communication check (signal loss detection) is not made.
· When the setting value is "0", monitor, parameter read, etc. can be performed. However, a communication error
(E.SER) occurs as soon as the inverter is switched to the network operation mode.
· A signal loss detection is made when the setting is any of "0.1s to 999.8s". To make a signal loss detection, it is
necessary to send data from the master within the communication check time interval. (The inverter makes
communication check (clearing of communication check counter) regardless of the station number setting of the data
sent from the master.)
· Communication check is started from the first communication after switching to the network operation mode (use Pr.
551 PU mode operation command source selection to change).
· Communication check time of query communication includes data absence time (3.5 byte).
Since this data absence time differs according to the communication speed, make setting considering this absence
time.
Example: RS-485 terminal communication, Pr. 539 = "0.1 to 999.8s"
Query communication
Operation mode
Programmable controller (master)
Inverter (slave)
Inverter (slave)
Programmable controller (master)
Communication
check counter
Broadcast communication
Operation mode
Programmable controller (master)
Inverter (slave)
Inverter (slave)
Programmable controller (master)
Communication
check counter
REMARKS
When using RS-485 terminal communication, inverter behavior at fault occurrence is different depending on the Pr. 502
Stop mode selection at communication error setting. (Refer to page 231)
260
External
Query Message 1
Pr.539
ALM
External
Query Message 1
Data absence time
(3.5 bytes or more)
Pr.539
ALM
NET
Query Message 2
Data absence time
(3.5 bytes or more)
Response Message1
Check start
NET
Query Message 2
Check start
Fault
(E.SER)
Response Message2
Fault
(E.SER)
Time
ON
Time
ON