Short Description of CANopen
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and "Stopped". After a "power-on", each CANopen devices is in the status "Initialization" and auto
-
matically changes to the Pre-Operational status. In this state the transmission of SDOs is allowed. If
the NMT master has set one or more nodes into the state Operational, they are allowed to transmit
and to receive PDOs. In the state Stopped no communication is allowed except that of NMT objects.
The state Initialization is divided into 3 sub-states. in order to enable a complete or partial reset of a
node. In the sub-state Reset Application the parameters of the manufacturer-specific profile area
and the standardized device profile area are set to their power-on values. In the sub-state Reset
Communication the parameters of the 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 val
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ues are the last stored parameters.
The
Heartbeat
protocol and
Node Guarding
are for error control purposes and signals the pres
-
ence of a node and its state. The Heartbeat message is a periodic message of the node to one or sev
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eral other nodes. It indicates 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.
4.2.2
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 avail
-
able for user data. The second and the following segments (using the very same CAN identifier) con
-
tain 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.
4.2.3
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). PDO trans
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missions may be driven by an internal event, by an internal timer, by remote requests and by the
Sync message received:
Summary of Contents for BL20-ECO
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