Talk:CANopen

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I think a few examples are extremely helpful. I added the CANOpen master querying a CANopen slave for current values, can someone please add how to configure a Node address?

4 TPDO's and 4 RPDO's

It says in the PDO section that there are 4 TPDO's and 4 RPDO's. This needs some clarification. AFAIK 4 is a default value. But what if a device only has one value to produce? Or is it is a device that produces data to many other devices?

My feeling is that this part needs some additions. —Preceding unsigned comment added by Rene.heijma (talk • contribs) 14:38, 2 January 2008 (UTC)

This is the number of default PDOs per device. The default TPDO mapping uses following COB-ID:s in sub-indexes 01h:
1800h: 180h + Node-ID (PDO1)
1801h: 280h + Node-ID (PDO2)
1802h: 380h + Node-ID (PDO3)
1803h: 480h + Node-ID (PDO4)

Of course you could use something else than Node-ID to sum there. But then you would quickly lose track on possible fieldbus conflict situations. Now you got the benefit of always knowing, where the TPDO arrives to the bus from. Correspondingly, if you need to receive TPDO1 in some node, you could configure RPDO1 if you know the node-id of the sending node.

But sometimes four isn't enough; then it's ok to use PDOs from 1800h to 19FFh. So actually, we aren't limited to four PDOs at all.[CiA DS-301].

-Mikko Laakso

"Upload/download" ambiguity

In control system parlance (ie PLCs), "download" means to send data away from you to another device - which is the opposite of its more common internet used where "download" means to bring data to you. So the description below is ambiguous and a diagram would be really helpful, if anyone has one.

The SDO protocol is used to set and read values from the object directory of a remote device. The device whose object directory is accessed is the SDO server and the device accessing the remote device is the SDO client. The communication is always initiated by the SDO client. In CANopen terminology, communication is viewed from the SDO server, so that a read from an object directory results in an SDO upload and a write to directory is an SDO download.

What is "M/O"?

In the first table, "M/O" is not defined. It is likely to be "Mandatory/Optional" --Mortense (talk) 14:05, 19 December 2011 (UTC)

What is the SDO block transfer performance advantage?

In "The SDO block transfer is a newer addition to standard, which allows large amounts of data to be transferred with slightly less protocol overhead." it would be nice to have "slightly less" quantified (e.g. is it 1%, 10% or 30% given some message sizes, etc.) --Mortense (talk) 14:36, 19 December 2011 (UTC)

No. of Nodes

"The CANopen standard divides the 11-bit CAN frame id into a 4-bit function code and 7-bit CANopen node id. This limits the number of devices in a CANopen network to 127."

7-bit are good enough for 128 nodes!? --62.216.165.53 (talk) 11:02, 22 December 2011 (UTC)

In this context the 0 is reserved for "all nodes". But do not misunderstand: This id split is only in the pre-defined connection. Since ids of PDOs can be configured, the rule is not always true. --JuergenKlueser (talk) 18:45, 22 December 2011 (UTC)