E-7
E.1.4.2 SDO (Service Data Object)
SDO is used to access the Object Dictionary in every CANopen node by Client/Server
model. One SDO has two COB-ID (request SDO and response SDO) to upload or
download data between two nodes. No data limit for SDOs to transfer data. But it
needs to transfer by segment when data exceeds 4 bytes with an end signal in the last
segment.
The Object Dictionary (OD) is a group of objects in CANopen node. Every node has an
OD in the system, and OD contains all parameters describing the device and its
network behavior. The access path of OD is the index and sub-index, each object has
a unique index in OD, and has sub-index if necessary.
The request and response frame structure of SDO communication is shown as
follows:
Type
Data
0
Data
1
Data
2
Data
3
Data
4
Data
5
Data
6
Data
7
7
6 5
4
3 2 1 0 Index Index
Index
Data Data Data Data
command
L H Sub LL LH HL HH
Initiate Domain
Download
Client
0
0 1
-
N
E S
Server
0
1 1
-
-
- - -
Initiate Domain
Upload
Client 0 1 0
- -
- - -
Server
0
1 0
-
N
E S
Abort Domain
Transfer
Client 1 0 0
- -
- - -
Server
1
0 0
-
-
- - -
N: Bytes not use
E: normal(0)/expedited(1)
S: size indicated
