Re: CANOpen PDO assignment.
David Harris <[email protected]>
| Newsgroups | gmane.comp.hardware.bus.can |
|---|---|
| Message-ID | <CAA_RDQV_eWKqB1Y69yhfWP9tOGm7Xx+M24V2xaG+JhKURZ_OaQ@mail.gmail.com> |
I am not sure I follow. However, one way out of your dilemma might be to consider the master to be the node with the higher nodeID. Does that help? David On Mon, Oct 29, 2012 at 11:31 PM, David Harris <[email protected]> wrote: > I am not sure I follow. However, one way out of your dilemma might be to > consider the master to be the node with the higher nodeID. > Does that help? > David > > On Mon, Oct 29, 2012 at 10:19 PM, John Dammeyer <[email protected]>wrote: > >> ** >> I've been trying to write up a short description on the difference >> between the standard transmit and receive PDOs and I'm having trouble >> explaining the difference. Here's why. >> >> From a master/slave perspective a transmit PDO is one the slave sends to >> the master. The receive PDO is the one that it programs in a filter so >> that the message makes it through to the slave. >> >> For the Master, each Transmit PDO is really a receive PDO and each >> Receive PDO is really a Transmit PDO. >> >> But I've always thought one of the up sides of CANOpen is that it >> functions well as a masterless system. So two slave class devices can use >> PDOs to hold multple bits of information and other slave devices pick out >> what they need. Who uses the standard Transmit PDO and who uses the >> Receive and for which direction? >> >> As each message on the bus has to be unique the sender of the PDO will >> always put their Node ID in the bottom 7 bits of the COB ID. You really >> can't have two nodes both sending a 0x182 Transmit PDO message so Node 3 >> will send 0x183 and node 5 will send 0x185. IfNode 3 needs the information >> in the Transmit PDO from Node 5 it's going to set filters to receive the >> message with that COB ID. Or should node 5 also be sending identical >> information in a Receive PDO 0x205? >> >> In trying to explain this I end up thinking the concept of default >> Transmit and Receive PDOs are redundent and they should have been just >> named PDOs without the Transmit or Receive adjective. >> >> Or am I missing something? >> >> John Dammeyer >> >> >> >> >> *"ELS! The Solution" >> *Automation Artisans Inc. >> http://www.autoartisans.com/ELS/ >> Ph. 1 250 544 4950 >> >> > >