BECKHOFF FC9001-0010 - Manual (Page 42)

Configuration via TwinCAT System Manager
4.5 Diagnostics tab
State
INIT: Initiate
PRE-OP: Pre Operation
SAFE-OP: Safe Operation
OP: Operation.
CRC A
Cyclic Redundancy Check at the incoming EtherCAT connection.
CRC B
Cyclic Redundancy Check at the outgoing EtherCAT connection.
CRC C
Cyclic Redundancy Check at the branch EtherCAT connection (if present).
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