[etherlab-users] Lack of Understanding: PDO Configuration

Richard Hacker ha at igh-essen.com
Thu Feb 10 22:30:42 CET 2011

On Thursday 10 February 2011 18:02:32 Viktor Rees wrote:
> Hallo,
> Question: When is PDO configuration necessary?
> In the mini.c examples for each slave the function ecrt_slave_config_pdos()
> is called. I am not sure in which cases this is really needed.
> Using  'ethercat cstruct' all the necessary information is displayed. So
>  the slaves themselves know their PDO configuration already. Therefore i
>  suppose that PDO configuration is not needed in most cases. Is that right?
> For my understanding, can you please tell when an explicit configuration is
> needed?
You are quite right in assuming that the master should scan the PDO 
configuration itself (which it does anyway). There are however 2 cases I can 
think of when it is necessary:
1) to allow for the case where the application can be started without any 
slaves being attached.
2) to make sure that the bus configuration is exactly how the application 
expects it to be.

The function 'ethercat cstruct' is simply a convenience tool that generates 
bug free code exactly the way the bus is configured at the time of execution. 
You can include this in your code instead of having to punch it in manually 
(with bugs ;) )

- Richard
> Thanks
> Viktor
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> etherlab-users at etherlab.org
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