Chapter 15 CANopen Overview
MH300
SDO (Service Data Objects)
Use SDO to access the Object Dictionary in every CANopen node using the Client / Server model.
One SDO has two COB-IDs (request SDO and response SDO) to upload or download data between
two nodes. There is no data limit for SDOs to transfer data, but it must transfer data by segment when
the data exceeds four bytes with an end signal in the last segment. MH300 series does not support
segmented transmission at the moment.
The Object Dictionary (OD) is a group of objects in a 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 in the OD is the index and sub-index; each object has a unique index in the OD, and has
a sub-index if necessary. The following shows the request and response frame structure of SDO
communication:
Type
Segmented
Segmented
Pause segment
N: No bytes used; E: General (0) / Transferred (1); S: Data size
PDO (Process Data Objects)
PDO communication can be described by the producer / consumer model. Each node of the
network listens to the messages of the transmission node and distinguishes whether the message
has to be processed or not after receiving the message. A 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 an
RxPDO. PDOs are transmitted in a non-confirmed mode. All transmission types are listed in the
following table:
Type Number
PDO
Cyclic Acyclic Synchronous Asynchronous RTR only
0
1–240
241–251 Reserved
252
253
254
255
Type number 0 indicates the synchronous aperiodic message between two PDO transmissions.
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.
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