Baumer BA_DSRT_22DJ - Handbuch (Seite 16)

Manual_CANopen_StrainLink_EN_V3_05.doc 16/65 Baumer
22.07.11/dam Frauenfeld, Switzerland
Excerpt of the object region for communication (1000H … 1FFFH)
Indexrange Description
1000h bis 1029h general communication objects
1200h to 12FFh SDO Parameter objects
1300h to 13FFh CANopen Savety objects
1400h to 1BFFh PDO Parameter objects
1F00h to 1F11h SDO Manager objects
1F20h to 1F27h Configuration Manager objects
1F50h to 1F54h Program control objects
1F80h to 1F89h NMT Master objects
4.4 Communication mechanisms
Differentiation is mainly made between two different types of data transmission. The Process Data Objects
(PDOs) are used to transmit real-time data or process data and the Service Data Objects (SDOs) allow
access to the object directory containing all device settings.
In addition to the standard transmission mechanisms, there are still more communications mechanisms.
These are Network Management (NMT), Emergency (EMGY), Node Guarding and Heartbeat.
4.4.1 Process Data Objects (PDOs)
The main task of a CANopen system is exchanging process data.
For the transmission of process data, the protocol overhead is omitted and transmission uses the Producer-
Consumer principle. This means that a message sent by a node (the Producer) can be received by all other
nodes (the Consumers). This principle is also known as broadcast and represents a very efficient principle of
data transmission.
PDO messages are not acknowledged to reduce the bus load as much as possible, primarily during time-
critical applications. Consequently, this service is not a query-response mechanism.
The transmission of PDOs is possible only in the Operational state and the transmission packets do not have
a fixed data length. The data length of a PDO can range from one to eight bytes.
With regard to the composition of the data packets, both the sender and the receiver must know how to
compose or interpret, respectively, the contents. The sender of the PDO can be identified only by the COB
ID.
PDO mapping describes the individual process variables transmitted in the data field of a PDO, how they are
arranged as well as the data type and length used. The contents and the significance of the transmitted data
in a PDO are defined in a PDO mapping list both on the send and the receive ends.
The transmission of process data can be triggered by various events:
•
Event driven
The transmission of the PDOs is triggered by an internal event of the node. This can occur due to a
timer in the device, by exceeding or dropping below a limit or through other internal events.
•
Synchronized
A bus user (usually the master) transmits synchronization messages on the bus. In the case of
synchronous transmission, the PDOs are triggered by the received sync message. In this way, it is
possible to obtain an instantaneous snapshot (process values at the same time) of the system.
•
Request driven
In this case, a bus user requests processed data using a Remote Transmission Request (RTR). This
mechanism is deprecated and not implemented by the strain links.