Re: CANOpen PDO assignment.

Am Mittwoch 31 Oktober 2012, 11:33:04 schrieben Sie:
> Heinz,
> 
> So my assumption about the Device's point of view is correct.  Alright.
> That makes sense from a Master/Slave perspective.
> 
> And if a number of Devices also use information from other devices?  Then
> the model falls apart right?
> 
> For example.  Three devices all send 3 PDOs with their digital inputs and
> analogue inputs as per 401.  One of the inputs on each node is a START
> button spread along a long fabrication machine.  They each use TPDOs:
> 180+node-ID
> 280+node-ID
> 380+node-ID
> 
> Now the nodes have to use TPDO COBIDs with the respective NodeIDs to
> capture this START button event.
> 
> My question and point was I guess, that as long as you maintain a
> Master/Slave architecture the TPDO, RPDO concept works.  As soon as you
> start having inter-device (slave to slave) communications the TPDO, RPDO
> concept breaks down.
> 
> What started me thinking about this was when I was at the International
> CAN Conference someone mentioned how a CANOpen system could be designed to
> be completely masterless with the PDOs serving as the communication
> backbone for a system where say an A/D value from one device (TPDO) caused
> a motor to run at a certain speed (RPDO) while a third device displayed
> both status values from both devices (RPDOs).
> 
> OTOH, with a small master in place it receives the TPDOs from the A/D
> device and creates RPDOs for the Motor and Display devices.
> 
> And this brings up a new question.  What are CANOpen implementers actually
> doing with RPDOs and TPDOs.  Are 99.9% of the CANOpen systems really just
> Master/Slave?
> 
> 

No, they aren't.
CANopen lives from its configurability.
You have to configure, and this is done typically with the RPDOs,
The COB-ID and often the mapping too.
Most often you have digital Inputs mapped to a Transmit PDO lets say with Id 181.
Other nodes that should receive this one, one is putting this input RPDO to relays,
another node is only displaying these inputs


Node 1 has a (pre-defined) TPDO on 0x181
Node 2 a (configured) RPDO on 0x181
Node 3 a (configured) RPDO on 0x181

> 
> Thanks
> John Dammeyer


Regards Heinz
 I'll send you one of our CANopen training slides in some minutes.