RE: Transceiver FMS interface

Hi,

There are some driver issues that must be addressed.  If you are hot plugging your CAN nodes you have to ensure that the ground pin makes contact first.   What we found is that if the supply voltage is 24V-28V and the Power, CAN_H and CAN_L connections are made first there is a possibility just before the ground finally connects the CAN bus could see a momentary common mode potential of the 24V-28V power. 

For the 5V based CAN drivers that have a 42V maximum CAN bus voltage that's not an issue.

For the 3V CAN drivers that have a 16V maximum it can be.

Over the period of a year I think I went through more than 10 drivers on a number of  USB to CAN dongles that used a 3V CAN driver because we were hot plugging (for testing and configuring) with connectors that could make in any order.

OTOH, we hot plugged over 2000 nodes into 24V without issue since they had 5V CAN drivers.  And unfortunately we also lost almost 50 nodes in a heartbeat when power was applied to a cable that had developed a short circuit between the 48V rail (sitting at 56V charging the batteries) and CAN_H.

John Dammeyer

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of [email protected]
Sent: January-16-13 12:23 PM
To: [email protected]
Subject: Re: [CANLIST] Transceiver FMS interface

Hello

If you are going to connect anything to an existing CAN network, you can allways kill the communication. This is independant of which transceiver chip you are using. As long as uou make the right connections to CAN Hi, CAN Lo and CAN Gnd and the existing bus is capable to drive one extra device, there is no problem.

The ISO11898-5 standard only describes the "sleeping mode" when there is no communication on the bus. So you can use your devices in a low-power mode. It has nothing to do with extra protection.

As long as you are just listening on the bus, you will have no problem on the J1939 network. Sending messages on the J1939 network is mostly not appreciated by the truck manufacturers. If you put your CAN controller in the listen-only mode, you will not be able to send any message, but if your software is not sending anyway this not really needed.

The listen-only mode is normally only used as long as you are not sure that all parameters are correctly. If you have some problem, like bitrate or CAN Hi and CAN Lo crossed, with your device it will be going to send error messages on the bus and so have influence on the bus. In the listen-only mode this will not be the case. However if you see that you are receiving messages and no errors (your Rx error counter = 0), there will be no problem to switch to normal mode.

As long as you don't have to connect to the bus used in the connection between truck and trailer (ISO11992) there is no physical difference between the busses.

So I advise to use the same hardware for both ports. Possible problems are mostly created in the software.

Hope this information helps.

Kees Zagers



fflinera schreef op 16.01.2013 18:03:
> My objective is to design a FMS interface device.
> I have planned to use a microcontroller with two CAN modules: one for 
> the CAN/J1939 interface with the truck/bus network and the other for 
> the CAN/FMS output.
> My doubt is about which transceivers I must use in each part.
>
> For the CAN/FMS output, I suppose that a typical ISO11898-2 compatible 
> transceiver is OK (a PCA82C251 for example).
>
> But, for the CAN/J1939 interface, I think we need to use something 
> special, because I must ensure that my device does not disturb the 
> operation of the Truck/bus CAN network in case of failure.
>
> I think that these 2 options are possible:
>
> 1. To use an ISO11898-5 compatible transceiver like TJA1043 from NXP.
> In this case, a bus failure can be detected and the FMS node can be 
> disconnected of the internal bus by the microcontroller.
>
> 2. To use an standard ISO11898-2 compatible transceiver (PCA82C251), 
> but the Microcontroller CAN module mus be programmed in "listen only"
> mode. in this case, What would happen  if the transceiver causes an 
> internal vehicle network failure?
>
> Please, Can anyone guide me whether any of these two options is 
> correct or is there better solutions?
>
> Thanks in advance.
>
>
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Report any problems to <[email protected]>