Chapter 15 CANopen OverviewMS300
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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. However, MS300 series does not
support transferring data by segment.
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.
N: Bytes not used; E: normal (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 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 does not support this transmission format.
Type number 255 indicates the data is an asynchronous transmission.
All PDO transmission data must be mapped to the index with Object Dictionary.
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