1 Topic by nicolas0481

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Topic: Can Bus Harware- How to know if terminations resistors are required

Hello,

Maybe this post is on wrong place of the forum but...

How could I know if termination resistor is required as soon as I try to do kind of 'man in the middle' with CANNY 7.2 Duo?
I would try to cut out the existing bus wires and place CANNY 7.2 Duo with two CAN interfaces (Gateway) to try to filter out some data.
But I have no idea if I have to set resistor jumpers on CANNY7, because I don't know where 'real' termination resistors are located in the bus real bus.
'Trial & error' method  (try en see) should be avoided.

Thank you
Regards
Nico

2 Reply by Konstantin, CANNY logic (edited by Konstantin, CANNY logic 29-01-2021 12:24:33)

  • Konstantin, CANNY logic
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Re: Can Bus Harware- How to know if terminations resistors are required

Hi Nico,
The high-speed HS-CAN (>100kbaud) requires terminating resistors. In case you are installing the controller "in-cut" of the existing CAN network, you must make sure that the resulting network will satisfy the attached scheme.  You can temporary disconnect car battery and check resistance on cut CAN segments.
The CANNY 7.2 Duo board already has 120 Ohm terminating resistors for each CAN interface, but they are disconnected by default. To connect them, you need to connect the solder jumpers on the back of the board.

I will move this topic to CANNY 7.2 Duo forum if you do not mind.

Updated: typo

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duo_term.jpg, 70.13 kb, 438 x 564
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3 Reply by nicolas0481

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Re: Can Bus Harware- How to know if terminations resistors are required

Hello Konstantin,

Thank you for your reply!

Yes I noticed on the wiki that there are jumper on the PCB. It looks like a very good tool, just ordered, I can't wait to receive it...

If I cut (at x mark) the bus I could encounter for example:
A-----x                    x-----B
         120ohm       120ohm                  So I have to put the termination resistors on CAN0&CAN1
A-----x                    x-----B

A-----x                    x-----B
          ~Hi-Z         60ohm                    In this case I should put the R on the 'Hi-Z' side but should it be 120 or 60 ohm?
A-----x                    x-----B


Sorry for the ASCII Art...:-)


Where are the termination resistors usually located in a car?Cluster, Gateway?


No problem to move the topic


Best regards
Nico

4 Reply by Konstantin, CANNY logic

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Re: Can Bus Harware- How to know if terminations resistors are required

You no need to put resistor in second case. But in this case it's recommended use as short CAN-H CAN-L wires as possible.
I do not know about some standard used by car manufacturers related to fixed places of this resistors. In theory this resistors must be placed on mostly distant from each other ends of bus.

Konstantin, CANNY logic's Website