CAN "BusOff" Error

NETMF & Gadgeteer
1

Hello,

I’m trying to interface fez cobra ii with pe3 ecu, using SN65HVD230 tranciever*.
Before trying to connect to the ecu, I verified that the communication is working by making a loop test - CAN1->CAN2 both via the transceivers and everything worked fine.
But, when I try to connect to the ecu, I get “BusOff” Error.

Something that I don’t understand is, is the fact that I got the error at least means that something IS working? I mean, it did recognize that something is not right…

*Rate of communication - 250kbps according to the ecu’s datasheet. no special configuration in the ecu required.

Code is here: pastebin.com/r7GyYykq

Any help would be much appreciated.

2

The only reason would be the bit timing.

Which product and which sdk are you using?

3

Thanks for the quick reply!

I’m using fez cobra 2,

ClrInfo.clrVersion:                     4.2.0.0
ClrInfo.clrVendorInfo:                  Microsoft Copyright (C) Microsoft Corporation.  All rig
ClrInfo.targetFrameworkVersion:         4.2.0.0
SolutionReleaseInfo.solutionVersion:    4.2.11.1
SolutionReleaseInfo.solutionVendorInfo: Copyright (C) GHI Electronics, LLC
SoftwareVersion.BuildDate:              Oct 23 2013
SoftwareVersion.CompilerVersion:        410713
4

I’ve just noticed that maybe that the BRP value is not correct.

Can you verify that this is correct?

[em]For the G120 this would be:

125KB - T1 - 15 - T2 - 8 - BRP - 20
250KB - T1 - 15 - T2 - 8 - BRP - 10
500KB - T1 - 15 - T2 - 8 - BRP - 5
1000KB - T1 - 7 - T2 - 4 - BRP - 20[/em]

Source:https://www.ghielectronics.com/community/forum/topic?id=1504

5

CAN timing is critical for a good working system and all devices must use the same BIT RATE and “sampling point”.

A rate of 125Kbps for example using a 75% sampling point won’t talk to a 125Kbps system with an 85% sampling point.

What is the sampling point setting for your ECU?

6

I’ve checked all over the datasheet of the ecu, and it doesn’t say a thing about “sampling point”. The only thing mentioned is in this “CANBUS Application Note”:

www.pe-ltd.com/joomla/images/downloads/AN400_CAN_Protocol_B.pdf

that the rate is 250 kbps.

7

These values are correct for G120 and framework 4.2.

8

Thanks! for which sampling point are those values?

9

Nice one. Your protocol is based on J1939 so I found this on a website

J1939 CAN Parameters

SAE J1939-11 and -15 specify a network data rate of 250 Kbps with a minimum period of 3.998 us and a maximum period of 4.002 us. CAN networks also allow and require for custom sample point settings. For J1939, the sample point setting has a maximum value of 87.5%. Nodes should be set as close as possible but not exceed 87.5%. CAN peripherals also allow for synchronous jump width (SJW) settings of 1 to 3. The SJW value dictates how much time can be added or subtracted to the node’s CAN clock for syncronization purposes. J1939 allows only for a single SJW.

This is the website

Once you set your sampling point to this I am sure you’ll get it working. Good luck.

10

@ jonkerbox2 -

I don’t remember on witch sample point these values were calculated but i’m using this settings in automotive communication witch is SAE J1939.

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11

Thanks!

To calculate I use this calculator: http://www.kvaser.com/support/calculators/bit-timing-calculator/
with the settings: 120MHZ,250kbps,0% allowed tolerance, MCP2510 (there is no option for SN65HVD230).
According to SAE J1939 sampling point should be 87.5% and SJW=1. This leaves me with only one option:

T1=14-1=13 (minus 1 because of sync)
T2=2
BTQ=16.

Now all I need is calculate BRP.
Clock after pre-scaler is: BTQ250kbps=15250kbps=4Mhz
That means that BRP=120/4=30.

Can anyone verify?

12

OK, I will try with the following settings: 250KB - T1 - 15 - T2 - 8 - BRP - 10
and let you if it works in couple of hours. Thanks very much for your help.

13

It worked! Thank you very much!

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