Re: CANopen PDO assignment.

Hi John,
up to  the second last section you gave a perfekt summary.
But
> Each node as 8 PDOs that it can use as TPDOs.
Is not correct.
As already explained, each node can have 4 TPDOs and 4 RPDOs
as pre-defined PDOs.
But can have more than 8 in sum or even more than 8 TPDOs.
In this case the system designer has to ensure that all TPDOs 
are configured with parameters fitting to all other nodes
especially to have no Id conflicts.

 Regards
     Heinz  

Am Donnerstag, 1. November 2012, 03:45:21 schrieb John Dammeyer:
> Hi Bertil,
> 
> If anything the slides support the idea that the default PDO descriptors
> are not really relevant.  They may well have been a mechanism to simplify
> the design of slave devices that didn't have the more modern features of
> larger EEROM and in circuit rewriteable FLASH.  ie. EPROMs erased with UV
> light and programmed outside the end product.
> 
> From a typical master/slave perspective, where slave PDOs aren't
> dynamically configurable and only talk to masters, it all makes sense.
> But today  we live in a world where we often choose a 32 bit processor
> with features in a 80 pin TQFP package that make it more power than the
> masters that were around when CANOpen was designed.  PLCs now have full
> TCP/IP stacks with email and FTP support and CAN is only one small part of
> it.  Firmware is upgraded in place from Micro-SD cards or TCP and
> sometimes even CAN.
> 
> And a RPDO data structure has to be configurable in order to know which
> COB ID to 'receive'.  That value might be programmed into a filter or mask
> to receive a group of COB IDs.
> 
> So to generalize, PDOs occupy the COB ID space from 181 to 5FF.  When the
> node is configured to receive and act on some of the of a specific COB ID
> data then inside the node it's referred to as an RPDO.  A PDO designed to
> be sent by a node on a periodic basis, by event or synchronized by a SYNC
> message is termed a TPDO by the node.  All PDOs have the originating 7 bit
> NODE ID # as part of the TPDO and TPDOs are the only PDOs actually sent on
> the bus.
> 
> In other words an RPDO is never transmitted.  It's just the name for a PDO
> that is received and inside the node defines how the data part is used.
> Pretty well every CANOpen network needs some level of configuration
> including devices that need the 7 bit ID part of an RPDO COB ID programmed
> so they know which message to accept.  Each node as 8 PDOs that it can use
> as TPDOs.  It can receive and act on COB IDs from 181 to 5FF excluding
> those with their own NODE ID.
> 
> John Dammeyer
> 
> "ELS! The Solution"
> Automation Artisans Inc.
> http://www.autoartisans.com/ELS/
> Ph. 1 250 544 4950
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