RE: Fwd: CAN HW compability

I would really start by figuring out which transceiver is exactly in use and work with that one rather than trying to fit a square peg in a round hole. I don’t see why the MCP2561 would work where the MCP2551 wouldn’t. 

 

Also, I did not say to use “highest termination”, but rather:

*         On the side of the network with only your node and the parking module (two nodes) you need to choose the LOWEST termination supported by the transceiver (for the TJA1054 that would be 500 ohm) because you need to get the bus termination value as close as possible to 100 ohms, and your parking module has already built-in resistors sized for a network with a whole lot more nodes.

*         On the side of the network with the rest of the nodes you can assume that the network is more or less already balanced and you just need to compensate for the parking module that you disconnected. So you pick a HIGH termination on that side as not to disturb the network too much.


If your PCB is limiting you to MCP2551 (or pin-compatible) transceivers, you should adapt the design or choose a different device to work with.

 

cheers,

Bram

 

From: [email protected] [mailto:[email protected]] On Behalf Of Job Race
Sent: maandag 11 mei 2015 15:30
To: [email protected]
Subject: Fwd: [CANLIST] Fwd: CAN HW compability

 

Thank you Daniel for your very detailed response. It makes very much sense. 

 

Looking at the MCP2551 transciever it reads: "The MCP2551 is a high-speed CAN, fault-tolerant device"

Which is a little confusing sense it seems it can't be both high-speed  and fault tolerant, but reading a little more its seems (to me) the meaning is the transciever is hight speed (ISO 11898-2) with fault tolerant capabilities that are not related directly to the ISO specifications (e.g. Detection of ground fault)

Anyway, the MCP2551 has a pin to pin replacement called the MCP2561 which is ISO-11898-5 compatible. I know it is not a fault tolerant transciver (i.e. ISO 11898-3) but i am wondering if it is a "little more" compatible

 

Also, if i were to summarise your given options:

1.	Replace the transciever to support FT CAN (ISO 11898-3) and try to figure out the correct termination to be used
2.	Use the highest termination and shortest cables as possible and hope for the best

1.	Actually it is exactly what i have done. i used the no termination (the natural transciever termination is about 47kohm) and shortest cables. As mentioned in previous mail it seems to work but the signal looks very bad via the osciloscope

If there are any other notes i will be happy to hear 

Best Regards