Short description of CANopen
D301087 0308 - BL20 CANopen2-4
communication profile area are set to their power-on values. The
third sub-state is initializing, which a node enters automatically after
power-on. Power-on values are the last stored parameters.
The Heartbeat protocol is for error control purposes and signals
the presence of a node and its state. The Heartbeat message is a
periodic message of the node to one or several other nodes. It indi-
cates that the sending node is still working properly.
A device sends the Boot-up message to indicate to the NMT
master that it has reached the state Pre-operational. This occurs
whenever the device initially boots-up but also after a power-out
during operation. The Boot-up message has the same identifier as
the Heartbeat object, however, its data content is zero.
Service Data Objects (SDOs)
A Service Data Object (SDO) reads from entries or writes to entries
of the Object Dictionary.
The SDO transport protocol allows transmitting objects of any size.
The first byte of the first segment contains the necessary flow
control information including a toggle bit to overcome the problem
of doubly received CAN frames. The next three bytes of the first
segment contain index and sub-index of the Object Dictionary entry
to be read or written. The last four bytes of the first segment are
available for user data. The second and the following segments
(using the very same CAN identifier) contain the control byte and up
to seven bytes of user data. The receiver confirms each segment or
a block of segments, so that a peer-to-peer communication (client/
server) takes place.
Process Data Objects (PDOs)
Process Data Objects (PDOs) are mapped to a single CAN frame
using up to 8 bytes of the data field to transmit application objects.
Each PDO has a unique identifier and is transmitted by only one
node, but it can be received by more than one (producer/consumer
communication).
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