pdo details

[can can canopen]

Hi All,
 
I am working on CANopen protocol,
 
Here they say that PDO's are used for real time data transfer,what does it mean by real time data transfer in the network.
In NMT PDO's are allowed only in Operational stage,what happens when operational state gets activated,what is Pre-operational if then?
In Pre-operational SDO objects can be read as well as written if parameter is RW.In what way SDO are different from PDO?
 
 
There is upload request and response in this format,
 
COBID    DLC      Command      Object L          ObjectH     Sub-Index       Data0    Data1    Data2      Data3
 
How can i get this type of message with the helpof Canopen functions.
 
Please help me out in both the matters.
 
Thanks in advance

[DirkW]

SDOs are normaly used to read and write configuration data to or from your CANopen Slave. The ID used for these services is much higher then the IDs used for PDOs. Therefore these PDOs have a higher priority on your CAN BUS and can be used to write and read Process data from an to your CANopen Slave. SDOs need the preoperational state before your Slave can handle them. PDOs need the operational state for your Slave in order to work.
You have to set these NMT states before you execute any write or read operation.
For your request and response format:
COBID = SDO ID +node ID -1 (1537+nodeID(1) -1 = 1537(0x601)
DLC = Data Length Code (8 = 8 Byte Data)
Command = Request/Response Code (0x40 = Read Request), (0x23 = Write Request with 4 Byte Data)
ObjectL = Object Index Low Byte  (0x08 - Low Byte Manufacturer Device name)
ObjectH = Object Index High Byte (0x10 - High Byte Manufacturer Device name)
Sub-Index = Object Sub-Index  (0x0)
Data0-3 = 4 Data Bytes
See the Help for the CANopen LabVIEW Library for more information.
<a href="http://joule.ni.com/nidu/cds/view/p/id/948/lang/en" target="_blank">http://joule.ni.com/nidu/cds/view/p/id/948/lang/en</a>
DirkW

[DirkW]

Hi,
Configuration data is data to configure your CANopen Slave and process data is data for the outputs of your slave and from the inputs of your slave.
When the slave enters into pre-operational it has initialized the internal applications and communication protocoll. The pre-operational state does not trigger any further behavior. But it can only handle SDO requests at this time and not send emergency messages or PDOs.
When the slave enters into operational state&nbsp; it is fully functional and should start any services configured before.
There are plenty of documentation on the web regarding CANopen basics.
DirkW