baudratebuscan
I'm trying to connect an automatic car gearbox which is using the CAN bus at 250 kbit/s to car with bus speed 500 kbit/s.
Is it possible to have nodes with different speeds on the CAN bus?
If it is not possible to have different speeds, is there a way to accomplish what I want to do? Anyway, a starting point would be great.
High Speed CAN and Low Speed CAN has difference in Physical Layer implementation. Bosch's CAN standard talks about Data link layer and Network layer but it left out "Physical Layer". (IMO)Reason being, it could be optimizied in Future.
Coming to question, High Speed CAN is defined in standard ISO11898-2 while ISO11898-3 talks about Low Speed CAN.
High Speed and Low Speed does have differences in Baud Rate. High Speed works from 10kbit to 1Mbits/sec and Low Speed restricts to 125kbps. Another major difference is Termination Resistance. High Speed CAN requires 120 Ohm termination on the bus while Low Speed CAN devices are self terminated (Every Device has Termination). Termination Resistors are to avoid Standing waves which would be significant in case of High Speed and Longer Bus lengths which is not significant in case of Low Speed CAN. Another Difference is High Speed CAN won't work if there is problem in Wiring but Low Speed CAN can work on Asynchronous network as it is terminated/grounded at every node. That's why Low Speed CAN is called as "Fault Tolerant CAN".
CAN transcievers can be programmed to ANY value provided ALL devices on the bus are on same baud rate. (See this Question for details)
If you connect High Speed Device on Low Speed Device network and if All nodes on bus have same baud rate, This High speed device will generate error frames until you connect a 120ohm terminator. Otherwise there would not be any issue as both have same voltage levels.
The termination resistors' values are too low. They should be 120 ohm, not 60 ohm (for a total ohmic resistance of 60 ohm - if you measure between CAN-H and CAN-L with a multimeter with all power off you should get 60 ohm. At the moment you would measure 30 ohm).
If "Fiat Stilo instrument cluster" only contains a single device, it is important that the CAN adapter is participating on the CAN bus (for example, setting the ACK bit). In CANKing this is done by setting Driver Mode to Normal (not Silent):
However, as this is the default setting, it is probably already set to Normal. If the actual Kvaser adapter does not support silent mode then the setting does not matter if the version of CANking is sufficiently new, version 5.0 or later (2009-06-09).
Best Answer
Basic CAN protocol doesn't support nodes running at different bitrates:
The newer version of the protocol called CAN FD, provides support for flexible data rate, as its name suggests. Legacy CAN hardware is supported on CAN FD networks, however, it still has to run at a given fixed bitrate.
I think your only option is to buy a router. Here is an example of a CAN router which supports 4 channels with independent bitrate configuration.