Mitsubishi Electric FR-A820-00046 Instruction Manual page 800

(N) Operation via communication and its settings
Signal loss detection (Pr. 122, Pr. 336 "RS-485 communication check time interval")
● If a signal loss (communication stop) is detected between the inverter and computer as a result
of a signal loss detection, a communication fault (PU connector communication: E.PUE, RS-485
terminal communication: 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", communication from the PU connector is not possible. In the case of
communication by RS-485 terminals, reading, etc. of monitors and parameters is possible, though
a communication error (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 (for details on control codes, refer to page 5-616) from the
computer 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).
● Communication check is started at the first communication in the operation mode having the
operation source (PU operation mode for PU connector communication in the initial setting or
Network operation mode for RS-485 terminal communication).
Computer
Inverter
Fig. 5-314:
Instructions for the program
● When data from the computer has any error, the inverter does not accept that data. Hence, in the
user program, always insert a retry program for data error.
● All data communication, for example, run command or monitoring, are started when the com-
puter gives a communication request. The inverter does not return any data without the comput-
er's request. Hence, design the program so that the computer gives a data read request for
monitoring, etc. as required.
5 - 620
Example: PU connector communication, Pr. 122 = "0.1 to 999.8 s"
Operation Mode
External
Inverter
Computer
Pr. 122
Communication
check counter
ALM
Open cable detection
PU
Check start
OFF
Parameters
Fault (E.PUE)
Time
ON
I002739E