CAN-8x23 user’s manual (Revision 3.20, Ma r/08/2012) ------
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3.3 PDO Introduction
Based on the transmission data format of the CAN bus, the PDO can
transmit eight bytes of process data at one time. Because of the PDO
messages without overheads, it is more efficient than other communication
objects within CANopen and therefore used for real-time data transfer, such as
DI, DO, AI, AO, etc.
Communication Modes for the PDO
PDO reception or transmission is implemented via the producer/consumer
communication model (also called the push/pull model). When starting to
communicate in the PDO push mode, it needs one CANopen device to play
the role of PDO producer, and non device or more than one device to play the
role of PDO consumer.
The PDO producer sends out the PDO message after it reached the CAN
bus arbitration. Afterwards, each PDO consumer will receive this PDO
message respectively, and then message is processed by each device to
check whether it is needed or not (be dropped). In the PDO pull mode, one of
the PDO consumers needs to send out a remote transmit request to the PDO
producer. According to this remote request message, the PDO producer
responds the corresponding PDO message for each PDO consumer in the
CAN bus. The PDO communication structure figure is shown below.
Producer
Consumers
request
indication
indication
indication
data
Push model
response
confirmation
indication
indication
data
Pull model
request
Producer
Consumers
indication
request
request
Remote Transmit Request
