Mitsubishi Electric FR-A700 Instruction Manual page 636

Communication operation and setting
Open cable detection (Pr. 122, Pr. 336)
If disconnection (communication stop) is detected between the inverter and computer as a result
of disconnection check, a communication error (PU connector communication: E.PUE, RS-485
terminal communication: E.SER) occurs and the inverter output is shut off.
Disconnection check is made when the setting is any of "0.1s" to "999.8s". To make discon-
nection check, it is necessary to send data (control code refer to page 6-451) 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).
When the setting is "9999", communication check (disconnection detection) is not made.
When the setting is "0", communication from the PU connector cannot be performed. For com-
munication via the RS-485 terminals, monitor, parameter read, etc. can be peformed, but a com-
munication error (E.SER) occurs as soon as the inverter is switched to network operation mode.
Example PU connector communication, Pr. 122 = 0,1–999.8s
Computer
⇓ Data flow
⇓ Data flow
Computer
Fig. 6-226: Open cable detection
6 - 456
Operation mode External
Inverter
Inverter
Pr. 122
Communication
check counter
PU
Check start
Parameter
Alarm E.PUE
Time
I001220E