Can bus wiring terminating resistor question.

[jsimmons]

Ok so im trying to add multiple things to the can bus network and so far i have a ms3pro to racepak iqs3 on the can bus network. Id like to add an ardiuno and a microsquirt (as a i/o box) and the can bus shield i plan to use on the ardiuno i can either remove the resistor or switch it off (i cant remember) so this item isn't an issue. however, im assuming that the racepak also has one built in because i have it wired directly to my ms3pro and i have no issues with it. Now when i add the microsquirt to the system will i have the ability to "switch off" the resistor? Im not sure if you can "switch off" the resistor in the racepak. I havent found any mention of it in any of the documents i have for the racepak.

[paw]

Assuming you have Microsquirt V3, you would have to desolder R18 to remove the CAN termination. Check the "Microsquirt_Hardware-3.3.pdf" manual, Chapter "Schematics"

[Matt Cramer]

We've run a Racepak, CAN-EGT, and MicroSquirt all on the CAN network at the same time, all with their terminating resistors in place.

[racingmini_mtl]

We've run a Racepak, CAN-EGT, and MicroSquirt all on the CAN network at the same time, all with their terminating resistors in place.

It will likely work but it's not ideal. And you know that you can easily disable the terminating resistor on the CAN-EGT. The problem with the wrong number of terminating resistor is that you may be losing a part of your bus bandwidth without even realizing it. The CAN transport protocol is robust enough that you won't lose data but you may have a bunch of retransmission packets.

So if you can, use the correct number of terminating resistors. And I must say that I find it astonishing that a device such as a dash, which is very likely to be used with other CAN devices, does not have an easy way to disable the terminating resistor.

Jean

[Matt Cramer]

Yes, this was kind of a test of what a user could get away with rather than what's ideal.

[paw]

It will likely work but it's not ideal. And you know that you can easily disable the terminating resistor on the CAN-EGT. The problem with the wrong number of terminating resistor is that you may be losing a part of your bus bandwidth without even realizing it. The CAN transport protocol is robust enough that you won't lose data but you may have a bunch of retransmission packets.

So if you can, use the correct number of terminating resistors. And I must say that I find it astonishing that a device such as a dash, which is very likely to be used with other CAN devices, does not have an easy way to disable the terminating resistor.

Jean

I agree with Jean. In my work I've run CAN bus systems in pretty severe elecrical environments (like a few thousand Amps of PWM in the nearby AC motor cables) and proper termination method is essential for good performance and obviously cabling and grounding. As for CAN bus, automotive environment is actually pretty easy for it. It is robust like Jean said.
As for the RacePak dash I assume that RacePak being a well-recognised and distinguished brand with their own V-net sensor bus and accessories, they assume that the dash is only connected to a RacePak datalogger box and nothing else...just a guess.
But like Matt said he just wanted to do a test to see how it works with all resistors in place

[jsimmons]

Thanks for the replays. I'm going to have a look around the software for the racepak again and see if there is a way. I would rather not desolder anything on the microsquirt if i dont have too.

[jsimmons]

Okay so I figured out how to turn off the terminating resistor in the race pack but it's a giant pain in the ass. So when i first set up the race pack I used pre-configured channels and set the ECU type to megasquirt and the data link software. What you have to do is go through the setup and set the ECU type to user-configurable and then manually set up what channels you want to see. This also means entering the specific canbus groups and whatnot in the racepak software which I have no idea how to do. So I changed all the settings in the race pack and try to display Map but I didn't have a lot of time to mess with it and I wasn't able to get at the display on the racepak. Hopefully I will get off early tonight and I can play with it some and figure out how to get the channels all set up to display correctly.

Anyway under the EFI setup tab there is a selection for the terminating resistor and you can turn it on and off. That's the easy part the hard part's getting all the channels set up

https://www.miataturbo.net/megasquirt-1 ... how-91964/

[jsimmons]

If I get off early enough tonight I will grab some screenshots and show you guys exactly what I'm talking about..