Mitsubishi Electric 800 Series Instruction Manual page 584

Signal loss detection (Pr.539 MODBUS RTU communication check time
interval)
• If a signal loss (communication) is detected between the inverter and the master as a result of a signal loss detection, an
inverter communication fault (E.SER) occurs and the inverter trips.
• When the setting is "9999", communication check (signal loss detection) is not made.
• When the setting is "0", reading, etc. of monitors and parameters is possible, though a Communication fault (inverter)
(E.SER) occurs instantly when the Network operation mode is switched to.
• A signal loss detection is made when the setting is any of "0.1 s to 999.8 s". To make a signal loss detection, it is necessary
to send data from the master within the communication check time interval. (The inverter makes a communication check
(clearing of communication check counter) regardless of the station number setting of the data sent from the master).
• The communication check is made from the first communication in the Network operation mode (can be changed by Pr.551
PU mode operation command source selection).
• The communication check time by query communication includes a no data time (3.5 bytes).
This no data time differs according to the communication speed, so take this time no data time into consideration when
setting the communication check time.
Example: RS-485 terminal communication, Pr. 539 = "0.1 to 999.8 s"
Query communication
Operation mode External
PLC (master)
Inverter (slave)
Inverter (slave)
PLC (master)
Pr.539
Communication
check counter
ALM
Broadcast communication
Operation mode External
PLC (master)
Inverter (slave)
Inverter (slave)
PLC (master)
Pr.539
Communication
check counter
ALM
NOTE
• For the RS-485 terminal communication, the operation at a communication error occurrence depends on the Pr.502 Stop
mode selection at communication error setting. (Refer to
(N) Operation via communication and its settings
NET
Query Message1
Data absence time
(3.5 bytes or more)
Response Message1
Check start
OFF
NET
Query Message1 Query Message2
Data absence time
(3.5 bytes or more)
Check start
OFF
Query Message2
Fault
(E.SER)
Response Message2
Fault
(E.SER)
Time
ON
page 546)
Time
ON
583
PARAMETERS
5
GROUP
N