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SDO (Service Data Objects)
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
Initiate
Client
Domain
Server
Download
Initiate
Client
Domain
Server
Upload
Abort Domain
Client
Transfer
Server
PDO (Process Data Object)
PDO communication can be described by the producer/consumer model. Each node of the network
will listen to the messages of the transmission node and distinguish if the message has to be
processed or not after receiving the message. PDO can be transmitted from one device to one
another device or to many other devices. Every PDO has two PDO services: a TxPDO and a
RxPDO. PDOs are transmitted in a non-confirmed mode.
PDO Transmission type is defined in the PDO communication parameter index (1400h for the 1st
RxPDO or 1800h for the 1st TxPDO), and all transmission types are listed in the following table:
Type Number
Cyclic
0
1-240
241-251
252
253
254
255
Type number 1-240 indicates the number of SYNC message between two PDO transmissions.
Type number 252 indicates the data is updated (but not sent) immediately after receiving SYNC.
Type number 253 indicates the data is updated immediately after receiving RTR.
Type number 254: Delta CANopen doesn't support this transmission format.
Type number 255 indicates the data is asynchronous transmission.
Data 0
7
6 5 4 3 2 1 0
command
0
0 1 -
N
E S
0
1 1 -
-
-
-
0
1 0 -
-
-
-
0
1 0 -
N
E S
1
0 0 -
-
-
-
1
0 0 -
-
-
-
Acyclic
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Chapter 14 CANopen Overview AFE2000 Series
Data 1 Data 2 Data 3 Data 4 Data 5 Data 6 Data 7
Index
Index
Index
L
H
Sub
-
-
-
-
PDO
Synchronous
Asynchronous
○
○
Reserved
○
14-113
Data
Data
Data
LL
LH
HL
N: Bytes not use
E: normal(0)/expedited(1)
S: size indicated
RTR only
○
○
○
○
○
Data
HH
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