System manual CECX / Bus link module CECX-B-CO
NMT:
Network Management Telegram. One of the operating elements of the CA-
NOpen-specification. The network management is used to initialize the
network and to monitor the nodes.
SDO:
Service data objects make a service for the access to the object directory
available. Each CANOpen device requires at least one SDO server which
accepts and processes SDO requirements from other devices.
PDO:
Process data objects make available a faster option for transporting proc-
ess data when compared to SDO transfers with low priority and which are
overloaded with protocol data.
Bus load:
The bus load [%] specifies the temporal load on the bus line with telegrams.
It is recommended that the calculated bus load does not exceed 50%, to re-
tain sufficient reserves for the SDOs and the other messages.
34.4.2 CANOpen short description
CANOpen is a widely used CAN-application layer that was developed by
the association CAN-in-Automation (CiA, http://www.can-cia.org) and which
meanwhile has been accepted as international standard.
The CECX-B-CO supports CAN-protocols CANOpen in accordance with
DS301 V4.01 and device profiles in accordance with DS401 V2.0. These
can be downloaded at the address listed above.
34.4.2.1 Device model
CANOpen consists
of th
e protocol definition (communication profile) and
the device profiles that standardize the data content for the respective de-
vice class. The Process Data Objects (PDO) are used for swift communica-
tion of the input and output data. The CANOpen device parameter and
process data are structured in an object directory. The access on any data
of this object directory is made via these service data objects (SDO). Fur-
ther to these, there are a number of special objects (and/or telegram types)
for the network management (NMT), synchronization, error messages etc.
CECX-II 34-5
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