Delta CT2000 Series User Manual page 411

Chapter 15 CANopen Overview CT2000 Series
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:
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
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.
All PDO transmission data must be mapped to index via Object Dictionary.
EMCY (Emergency Object)
When errors occurred inside the hardware, an emergency object will be triggered an
emergency object will only be sent when an error is occurred. As long as there is nothing wrong with
the hardware, there will be no emergency object to be served as a warning of an error message.
Cyclic Acyclic
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PDO
Synchronous Asynchronous
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Reserved
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15-4
RTR only
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