Duet 3 Tool Board - CAN Connector & Step / Direction Outputs
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It's fun to speculate though. I'd suspect it was different priorities of communication - Configuration / status information on one and trajectory / motion control on the other.
So the 6HC has two CAN pairs on the same connector.
The 3HC has a processor which supports two CAN busses, but CAN connector pinouts on the wiring diagram only list the middle pair as CAN - The other pair is shown as "passthrough". It's also interesting to note that there are two termination resistor jumpers, presumably one per pair so that they can both be terminated even if they aren't both used by that board.
The tool board looks to take a single pair for passthrough and has no termination resistors.
The tool distribution board is where things get interesting. It has a pair of RJ11 connectors for passthrough, but only has a single termination jumper. Is it expected that only one CAN pair makes it to the tool distribution board? Is v0.4 of the tool distribution an old design that has since been updated and not put on the documentation site?
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@yngndrw said in Duet 3 Tool Board - CAN Connector & Step / Direction Outputs:
The 3HC has a processor which supports two CAN busses, but CAN connector pinouts on the wiring diagram only list the middle pair as CAN - The other pair is shown as "passthrough". It's also interesting to note that there are two termination resistor jumpers, presumably one per pair so that they can both be terminated even if they aren't both used by that board.
Perhaps I don't have the correct mental map for CAN. In order to daisy chain, would it not be true that the center pair of either connector has the potential to need to be a master?
It would be possible to 'force' and "in" v "out" connector... but... since the chosen chip has two can, both (either) of which can be master... why not eliminate one more support headache?
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@yngndrw said in Duet 3 Tool Board - CAN Connector & Step / Direction Outputs:
Configuration / status information on one and trajectory / motion control on the other.
Dave once commented that moves are sent about two seconds in advance. Doesn't seem to reflect a high need for prioritization.
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@Danal Yes in CAN any board could send a message at any time and therefore act as a master, with the message ID allowing for prioritisation / arbitration. (Lowest ID wins) I think you're right in that it would probably make life easier in there was a BUS in each direction so that's a fair theory.
The buffering of moves makes a lot of sense in this setup and that probably rules out the different prioritisations.
Maybe there simply isn't enough bandwidth over one bus for the number of expansion boards they'd like to support?
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@yngndrw said in Duet 3 Tool Board - CAN Connector & Step / Direction Outputs:
I do wonder why both of the CAN buses are exposed via the same connector on the 6HC - Are they intended to be used together to provide a low and high priority bus?
The reason was lack of space. The second CAN bus was a late addition and isn't supported in firmware yet. It's there so that we can provide a low speed CAN bus as well as the standard high speed CAN-FD bus, to give us the option of supporting CANopen devices in future. It would require an external adapter to split the two buses.
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@dc42 Ah I see, that makes sense! Does that mean that the tool distribution board is missing the second termination jumper that the expansion board has, or is that an old design in the documentation, or is it intended that the splitter would always come before the tool distribution board?
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@yngndrw said in Duet 3 Tool Board - CAN Connector & Step / Direction Outputs:
is it intended that the splitter would always come before the tool distribution board?
Yes.
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@dc42 Is there a rough timeline for the family board? I am very interested in this option to drive a brushed DC motor on a Stratasys uPrint from a Geckodrive G320x. I need those step/dir outputs to control the Gecko.
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@deckingman Looking at the documentation I don't see the step/dir outputs available for the tool board. I think @dc42 is referring to a separate board that will allow the step/dir outputs.
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@Archeantus Sorry - the title of this thread is "Duet 3 Tool Board - etc" so I assumed as you posted in this thread that you meant the tool board. Suggest you start a new topic so as to remove any confusion.
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@Archeantus See comment here https://forum.duet3d.com/post/131959
Basically, they are in the works, but focus was on getting the tool board finished. No timeline for delivery, yet.
Ian