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Process Data Object (PDO)
The time critical process data are transferred by means of the
"Process Data Objects" (PDOs). The PDOs can be exchanged
between the individual nodes in any way (PDO linking). It is also
defined whether the data exchange is event-controlled
(asynchronous) or synchronized. Depending on the type of data
to be transferred the right choice of the transmission type can
considerably relieve the amount of data transmitted on the CAN
bus. The default setting of the I/O modules from ifm electronic
gmbh specifies a synchronous transmission of analog input data
and all output data and an event-controlled transmission of
digital input data.
Node Guarding Object
To detect communication errors in the network node guarding is
used. Each bus node is cyclically accessed by the network
master via the defined node guarding COB ID. If no reply is
given within the defined guard time, the master signals an error.
Via the life time (life time factor * guard time) it can also be
defined after how many unsuccessful attempts the error
message is to be created.
Emergency Object
If an internal error occurs in a bus participant (e.g. wrong
configuration parameter, short circuit at the output) an EMCY
object is created. This EMCY object is standardized and is sent
once when the error occurs and once when the error state has
disappeared.
In the object directory of the node these errors are stored. To do
so, the "error register", the "manufacturer-specific status
register" and the "error history" are available.
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