6 Overview of the CANopen Protocol
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Index
Object
000 Not used
0001-001F Static data types
(
standard data types
,
such as Boolean
,
Integer16
)
0020-003F
Complex data types
(
structure composed of simple types
,
such as
PDOCommPar
,
SDOParmeter
）
0040-005F Manufacturer-
specific complex data types
0060-007F Device profile specific data types
0080-009F Device profile specific
complex
data types
00A0-0FFF Reserved
1000-1FFF Communication profile area
(
such as device type
,
error register
,
supported number of PDOs
)
2000-5FFF Manufacturer-specific profile area
6000-9FFF
Standardized profile area
(
such as "DSP-401 I/O module device
subprofile
:
Read State 8 Input Lines
)
A000-FFFF Reserved
Figure 6-2
Structure of the object dictionary
6.3 Common Communication Objects
1) Network Management (NMT) Object
The NMT objects include the Boot-up message, heartbeat protocol, and NMT message.
Based on the master/slave communication mode, NMT is used to manage and monitor
all nodes in the network, implementing node state control, error control, and node
startup.
2) Service Data Object (SDO)
With SDOs, the object dictionary entries can be accessed based on the index and
subindex.
The SDO is implemented using the CAN-based message specification (CMS) object of
multi-domain in the CAN application layer (CAL)
and can transmit data of any length
(segmented into several messages when the data length exceeds four bytes).
The SDO protocol produces a response for every request. The SDO request and
response always contain eight bytes.
3) Process Data Object (PDO)
PDO is used to transmit real-time data from one node to one or multiple nodes. The
data length is restricted to one to eight bytes.
Each CANopen device includes eight default PDO channels, that is, four TPDOs and four
RPDOs.
PDO supports synchronous transmission and asynchronous transmission, determined
by the PDO communication parameters.