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Service data Object SDO
Object dictionary bridges application and communication. All data entries of CANopen equipment
are managed by the object dictionary. Each object dictionary entry can be addressed by index or
subindex. CANopen defines the parameter setting of SDO mainly using on the master node to the slave
node. Service confirmation is the most distinguishing feature of SDO; it generates one response for
each information to secure the accuracy of data transmission.
In the CANopen system, this kind of communication mode for data exchange is based on
client/server structure. Generally, CANopen slave mode serves as SDO server and CANopen master
node as the client. The client visits the object dictionary on data server through “send SDO request” to
read/write a single object in the dictionary. The following is the flowchart of SDO write-in status
Process data object PDO
PDO uses producer-consumer model to transmit real-time data. The producer is responsible for
transmitting the information; for example, if data transmission is triggered by certain internal incident
of the equipment, all other buses monitor data sent on buses. The priority of PDO is determined by
corresponding CAN identifier (COB-ID). Whether the message (consumer) should be processed is
judged by respective identifiers. PDO can be divided to RPDO (receiving process data object) and
TPDO (transmitting process data object). TPDO and RPDO mentioned in the protocol are relative and
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