D301087 0308 - BL20 CANopen 2-3
CANopen
2
Communication
The lower layers of CANopen are defined according to the ISO-OSI
model in the ISO 11898 standard.
Communication between the individual nodes is made by transmit-
ting "Telegrams".
4 different types of telegram message are defined for CANopen:
Network management messages
Service data objects SDO
Process data objects PDO
Predefined messages
Network Management Messages
Network management messages are used in the network to control
the nodes and their operating states. This type of message makes it
possible, for instance, to configure the data transmission mecha-
nism of a node.
The Network Management objects include Boot-up message,
Heartbeat protocol and NMT message.
Boot-up message, Heartbeat and Node Guarding are implemented
as single CAN frames with 1-byte data field.
The NMT message is mapped to a single CAN frame with a data
length of 2 byte. Its identifier is 0. The first byte contains the
command specifier and the second contains the Node-ID of the
device that must perform the command (in the case of Node-ID 0 all
nodes have to perform the command). The NMT message trans-
mitted by the NMT master forces the nodes to transit to another
NMT state. The CANopen state machine specifies the states Initial-
ization, Pre-Operational, Operational and Stopped. After power-on,
each CANopen device is in the state Initialization and automatically
transits to the state Pre-operational. In this state, 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 three 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
To Next Page
Loading...
