Communications model
8 ATM60-Cxx 03/2007
5. Communications model
In CANopen, four classes of communications objects are defined:
· Process data objects (PDOs)
CAN communications objects (< 9 byte) for the transport of process data (application objects),
unconfirmed transfer of data between network participants. No protocol overhead. Content of the data
field specified by “PDO mapping”.
· Service data objects (SDOs)
Access to entries in the object directory of a device. Confirmed transfer of data of any desired length.
Two CAN identifiers per SDO object (channel). Specification of the object directory entry via index and
sub-index of the entry.
· Management objects
For tasks of network management.
· Predefined objects
For the synchronization of operations (synchronization object) and reporting device error states
(emergency object).
5.1 Process data objects (PDO)
For the ATM60-Cxx, there are two transmission PDOs, PDO 1 (tx) and PDO 2 (tx) are available for data
transmission. The content of the PDOs is specified by the respective “PDO Mapping” Object 1A00
hex
and
1A02
hex
.
The type of transmission of a PDO is specified via the sub-index 3 (transmission type) of the objects 1800
hex
and 1802
hex
(PDO communication parameter).
The following transmission types are provided:
· Synchronous transmission
Transmission is carried out on the basis of the synchronization object.
· Asynchronous transmission
Transmission is carried out without reference to the synchronization object. The transmission is
triggered by an internal timer or by a change in a position value.
· Transmission on request
The transmission is carried out only after the request from another participant has been received.
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