Mitsubishi Electric FR-F740-00023 Instruction Manual page 209

Communication operation and setting
(6) Retry count setting (Pr. 121, Pr. 335)
Set the permissible number of retries at occurrence of a data receive error. (Refer to page 199 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)
Operation mode
Computer
Inverter
Inverter
Computer
Example: PU connector communication, Pr. 121 = "9999"
Operation mode
Computer
Inverter
Inverter
Computer
LF
(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 signal loss
detection, a communication fault (PU connector communication: E.PUE, RS-485 terminal communication: E.SER)
occurs and the inverter trips.
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 198) 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 command source (PU
operation mode for PU connector communication in the initial setting or network operation mode for RS-485 terminal
communication).
When the setting is "9999", communication check (a 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 error (E.SER) occurs as soon
as the inverter is switched to network operation mode.
Example: PU connector communication, Pr. 122 = "0.1 to 999.8s"
Operation Mode
Computer
Inverter
Inverter
Computer
Pr.122
Communication
check counter
200
Wrong
Reception error
Wrong
OFF
External
PU
Check start
Fault (E.PUE)
Wrong
Reception error
Wrong
Reception error Reception error
ON
Normal
OFF
Fault (E.PUE)
Time