CANopen PDO

[gndfng]

Message Edited by gndfng on 04-16-2008 04:28 AM

[gndfng]

Hi I am Amit,

I am working on CANOpen Protocol.

I want to know the whether the PDO's are opened for transmission after receving the SDO?

[DirkW]

Hi In order to work with SDOs your CANopen Slave has to enter the preoperational state, however that doesn't allow PDO communication. Therefore you would need to enter into start communication state. In this state both SDO and PDO communication is possible.

DirkW

[gndfng]

Ya I agree to ur statement.

But my problem is, after entering into the operational state or after starting the node, how to start the PDO communication.

One more thing i want u to know is, i am working on PIC18F4680 & i have CANopen Slave Stack Software partially. I have to make it complete. In that actually there is a C function called "mTPDOopen(1)" which tells to the stack to open the PDO transmission. But in the stack, no where they have called this function, but they have declared in the Object Dictionary another function which inturn calls this function.

[DirkW]

If your Master sends the start communication command, your slave should go into operational state if it works correctly. From there a slave has typically more then one option to communicate with PDOs. These options are configurable with SDOs. It could start sending PDOs immediately, or wait for a RTR Frame to arrive or wait for a Sync frame to arrive. Does your Slave has a Object dictionary? There you should find the possible options.

DirkW

[gndfng]

Ya My slave has object dictionary.

According to u, when slave enters into the operational state after receing a msg frm master, for a slave to start the PDO transmission the master has to send the SDO right. 

[gndfng]

Thank u DirkW for interacting with me........., If u still support me a bit more then i will be very much grateful to u.............,

[DirkW]

The Master handles the Network  management and sends the message to one particular or all slaves to enter operational state. The slave then acts as configured in his object dictionary and starts sending PDO data or waits for a sync or RTR frame in order to answer with PDO data. The master can use SDOs to reconfigure these communication settings.

DirkW

[gndfng]

I agree that slave starts the PDO transmission after receving RTR or SYNC msg from master. What will be the contents of the RTR msg from master.

[DirkW]

A Remote Transmission Request (RTR doesn't have content since it doesn't contain any data bytes. it is just the ID together with the RTR Flag and the Slave answers with the same ID and Data.

DirkW