Mitsubishi Electric FR-A720-0.4K Instruction Manual page 350

(6) Retry count setting (Pr. 121, Pr. 335)
⋅ Set the permissible number of retries at occurrence of a data receive error. (Refer to page 338 for data receive error
for retry)
⋅ When data receive errors occur consecutively and exceed the permissible number of retries set, an inverter trip
(E.PUE) may occur and stops the motor.
⋅ When "9999" is set, an inverter will not trip even if data receive error occurs but an alarm output signal (LF) is output.
For the terminal used for the LF signal output, assign the function by setting "98 (positive logic) or 198 (negative
logic)" in any of Pr. 190 to Pr. 196 (output terminal function selection).
Example: PU connector communication, Pr. 121 = "1" (initial value)
Computer Inverter
Inverter Computer
ALM
Example: PU connector communication, Pr. 121 = "9999"
Computer
Inverter
Computer
Inverter
LF
ALM
(7) 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 cannot be performed. For communication via the RS-
485 terminals, monitor, parameter read, etc. can be performed, but a communication fault (E.SER) occurs as soon as
the inverter is switched to 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 (control code refer to page 337) from the computer within the communication check time
interval. (The send data has nothing to do with the station number)
⋅ 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).
Example: PU connector communication, Pr. 122 = "0.1 to 999.8s"
Operation Mode
Computer
Inverter
Inverter Computer
Communication
check counter
ALM
Wrong
Wrong
OFF
External
PU
Pr.122
OFF
Communication operation and setting
Fault (E.PUE)
Wrong
Reception error Reception error
ON
Wrong
Reception error Reception error
ON ON
OFF
Check start
Normal
Fault (E.PUE)
Time
ON
339
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