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3.3.
Connection and Disconnection
(1) The FR-EPN option unit is considered a slave device in the DeviceNet
communications standard. This means that it cannot send messages
out on its own and dictate the operations of other devices on the
network. A master device establishes a connection to the option unit,
sends commands, requests for information, etc., and finally disconnects
when communication is completed. The purpose of connection and
disconnection is to prevent two master devices from sending motor
control commands to the same motor at the same time. It is possible
for one master to control the motor while another reads monitor data
and parameters.
(2) The option unit operates somewhat independently of the inverter in that
a master may connect or disconnect while the inverter is in PU mode.
However, motor control commands from the network will not be
recognized unless the connection is made while the inverter is in
external mode.
(3) When the master device disconnects from the option unit or the option
unit loses connection due to some fault such as a network power
failure, the inverter continues with the last command received until the
timeout value is reached. This is set in the expected packet rate of the
DeviceNet connection object. For example, the master might send a
command to start forward at 60 Hz and then disconnect. The MNS
LED will be green during communication and switch to flashing green
upon disconnection. The motor will run at 60 Hz until the timeout
occurs or the master establishes a new connection and sends different
commands.
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