Mitsubishi Electric FR-D720S SC EC Instruction Manual page 350

Communication operation and settings
Retry count setting (Pr.121)
Set the permissible number of retries at data receive error occurrence. (Refer to page 6-211 for
data receive error for retry.)
When data receive errors occur consecutively and exceed the permissible number of retries set,
an inverter trips (E.PUE) and a motor stops (as set in Pr. 502).
When "9999" is set, an inverter fault is not provided even if data receive error occurs but an alarm
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, Pr. 192 or Pr. 197.
Example PU connector communication at different settings of parameter 121
Computer
⇓ Data flow
⇓ Data flow
Computer
Computer
⇓ Data flow
⇓ Data flow
Computer
Fig. 6-104: Data transmission error
NOTE
Pr. 121 is valid only when Mitsubishi inverter (computer link operation) protocol is selected.
Pr. 121 is not valid when Modbus-RTU communication protocol is selected.
6 - 200
PU connector communication, Pr. 121 = 1 (initial value)
Inverter
Inverter
PU connector communication, Pr. 121 = 9999
Inverter
Inverter
OFF
LF
Wrong Wrong
Reception error
Wrong Wrong
Reception
error
ON OFF
Parameter
Fault E.PUE
Reception error
Normal
Reception
error
ON OFF
I001354E