Image Processing Reference
In-Depth Information
Communication
Object
dictionary
Application
Application
object
State machine
Entry #1
Entry #2
Entry #3
Entry #4
Communic.
object
Communic.
Application
object
Application
object
Communic.
object
…
Entry #
n
Communic.
object
Application
object
CANopen device
Interface to
CAN network
Interface to
process
FIGURE .
Conceptual internal architecture of CANopen devices.
ease the system configuration, a predefined master-slave connection set must be provided by every
CANopen device, which consists of a standard allocation scheme of CAN identifiers to COBs and is
made available directly after initialization.
15.6.2 Object Dictionary
The behavior of every CANopen device is completely described by means of a number of objects,
each one tackling a particular aspect related to either the device configuration, the communications
on the CAN bus or the functions available to interact with the physical controlled system (e.g., there
are objects that define the device type, the manufacturer's name, the hardware and software version,
and so on).
All objects relevant to a given node are stored in the object dictionary (OD) of that node. As shown
in Figure ., interactions between frames exchanged on the CAN network and the local applica-
tions acting on the physical system take place through the OD. his enables a standardized view of
devices and their behavior for control applications, and an easy interaction with them through the
CAN network.
he OD can be seen as a big table, which stores all information characterizing a device. Both param-
eterization and process data are kept in the OD, which acts as the sole repository of information for
the device.
he OD includes up to , different objects, and each one of them is addressed through a unique
bit address. Any object, in turn, can either be of a simple type (integer, floating point, string, etc.)
or consist of up to subentries, each one addressed by means of an -bit-long subindex (arrays
and records). In the case of simple-type entries, subindex
h
is used to access the information. his
means that each subentry in the OD can be uniquely identified through a bit multiplexer.
From a conceptual point of view, the OD is split into four separate areas, according to the indexes of
entries. Entries below
h
are used to specify data types. Entries from
h
to FFF
h
(communica-
tion profile area), instead, are used to describe communication-specific parameters, i.e., they model
the interface of the device to the CAN network. hese objects are common to all CANopen devices.
Entries from
h
to FFF
h
(manufacturer-specific profile area) can be freely used by manufacturers
to extend the basic set of functions of their devices. heir use has to be considered carefully, in that
it could make devices no longer interoperable. Finally, entries from
h
to FFF
h
(standardized
